Poorly 350i... Still
Discussion
OK, I've been investigating a problem on someone's 350i for a while.
Symptoms started as a loss of power when slowing down and turning into roundabouts or corners.
The problem is intermittent.
When the revs drop the only way to recover is to use the movement of the car to spin the engine until she fires again.
If I open the bonnet and blip the throttle the revs drop and the engine sounds like it's gasping for air, if I open up the throttle slowly it will be fine, once revs are higher it runs pretty well with just the odd small mis-fire (pretty normal?).
On Saturday I started the car for the first time in a couple of months, she fired immediately and ran fine for a quick little five-mile jaunt. On Sunday she virtually refused to start. After a bit of wire jiggling I found that the LT connection to the coil was very loose. Replaced the terminals, engine started after a few turns and ran well for about ten minutes. Slowed down for a roundabout and ..... Loss of power!!!
I've fitted a new engine temperature sensor, replaced the throttle pot with one from my car, replaced some leaky vacuum hoses and a leaky fuel rail, all of which seemed to cure the problem, but didn't! The problem occurs mainly when the engine is warm (which explains why it apparently responded to various replacements) but will sometimes even give the problem from cold.
Any other suggestions before the owner gets the gallon of petrol and box of matches ready?
Symptoms started as a loss of power when slowing down and turning into roundabouts or corners.
The problem is intermittent.
When the revs drop the only way to recover is to use the movement of the car to spin the engine until she fires again.
If I open the bonnet and blip the throttle the revs drop and the engine sounds like it's gasping for air, if I open up the throttle slowly it will be fine, once revs are higher it runs pretty well with just the odd small mis-fire (pretty normal?).
On Saturday I started the car for the first time in a couple of months, she fired immediately and ran fine for a quick little five-mile jaunt. On Sunday she virtually refused to start. After a bit of wire jiggling I found that the LT connection to the coil was very loose. Replaced the terminals, engine started after a few turns and ran well for about ten minutes. Slowed down for a roundabout and ..... Loss of power!!!
I've fitted a new engine temperature sensor, replaced the throttle pot with one from my car, replaced some leaky vacuum hoses and a leaky fuel rail, all of which seemed to cure the problem, but didn't! The problem occurs mainly when the engine is warm (which explains why it apparently responded to various replacements) but will sometimes even give the problem from cold.
Any other suggestions before the owner gets the gallon of petrol and box of matches ready?
Never experience the problems myself but have you tried a known working coil ?
Mine was faulty, didn't know at the time...my fuses kept burning up.
A lecky friend told me to replace the coil and renew/improve the earth cable that it was bolted too.
no problems since but maybe no use to you.
best of luck.
Mine was faulty, didn't know at the time...my fuses kept burning up.
A lecky friend told me to replace the coil and renew/improve the earth cable that it was bolted too.
no problems since but maybe no use to you.
best of luck.
Edited by HOTTY on Monday 14th March 22:15
HMMMmm 
I was sort of considering the coil. In the past they've just died, but it's feasible that it's on it's way, or overheating! I'll have to take the one off my Wedge to try.
As far as the fueling is concerned, I'll have to take it somewhere that has a pressure gauge to stick in the fuel line.
I was sort of considering the coil. In the past they've just died, but it's feasible that it's on it's way, or overheating! I'll have to take the one off my Wedge to try.
As far as the fueling is concerned, I'll have to take it somewhere that has a pressure gauge to stick in the fuel line.
PoleDriver said:
HMMMmm
I was sort of considering the coil. In the past they've just died, but it's feasible that it's on it's way, or overheating! I'll have to take the one off my Wedge to try.
As far as the fueling is concerned, I'll have to take it somewhere that has a pressure gauge to stick in the fuel line.
There is a coil and ignition module on classifieds for £35I was sort of considering the coil. In the past they've just died, but it's feasible that it's on it's way, or overheating! I'll have to take the one off my Wedge to try.
As far as the fueling is concerned, I'll have to take it somewhere that has a pressure gauge to stick in the fuel line.
PoleDriver said:
As far as the fueling is concerned, I'll have to take it somewhere that has a pressure gauge to stick in the fuel line.
I bought an in-line gauge on the 'Bay a few weeks ago, one of these in fact...http://cgi.ebay.co.uk/FUEL-PRESSURE-GAUGE-TESTING-...
Because your current focus is on the ignition system and the fault is clearly intermittent, randomly replacing components may prove futile and unnecessarily expensive so I suggest you undertake a program of ignition component testing using very basic tools and equipment.
If that does not expose the problem, follow this up by an elegant but slightly more complex dynamic test process designed to uncover intermittent ignition faults.
After that you can move your efforts to fuelling.
Start with this fully comprehensive component test program:
TESTNG IGNITION COMPONENTS - BACK TO BASICS
The circuit represents BOTH the system where the amplifier is mounted in an aluminium housing behind the coil AND where it is mounted on the side of the distributor. The effective electrics are the same, just the physical locations of components differ.
Be sure the earths and the wiring from the ignition switch through to the coil, distibutor and amplifier module are pretty much the same as shown.
Getting Started
o Reasons for testing the ignition system are a proven loss of sparks at the spark plugs, or weak/intermittent sparks causing misfiring.
o To proceed, separate the Low and High Tension circuits to find out immediately which circuit is faulty, then persue the fault condition in either circuit according to the results of some logical tests.
o Remove the king lead from the distributor, connect it to a good spark plug and lay the plug on the engine somewhere.
o Switch on the ignition and crank the engine.
o Is there a fat spark at the spark plug.
o If Yes - then the problems are downstream and away from the king lead at the dizzy cap, rotor arm, plug leads, plugs, or ignition timing so that is where to look - see " Other Components" (later) for checking the usual suspects, inspect, clean, substitute and only replace if faulty.
o If No - change the king lead.
o If still No - then the problems are upstream from the king lead and towards the coil, amplifier, distributor innards or their local connections all the way back to the ignition switch.
Testing the Low Tension Side Voltage Feed
o Switch on the ignition and use a multimeter to verify there are 12 volts at coil positive.
o If No - find out why, by checking the circuit between coil positive and the ignition switch and beyond, all the way back to the battery if necessary, for corroded or loose/broken connections.
o If Yes - dont take it for granted, waggle local wiring and toggle the ignition switch a few time to ensure the voltage is reliable, even using a bright lamp to check the wiring can supply a load.
Test the coil independently
o Disconnect the wire from coil negative to the amplifier.
o Turn ignition on, and strike coil negative to earth with a flying lead to see how good is the king lead spark.
o If sparks are absent/poor/weak and +12 volts is still present at coil positive then the coil is prime suspect for inspection/replacement.
o If sparks are fat/healthy then coil must be OK, so look for amplifier/pickup coil problems.
Test the Amplifier and Distributor Pickup Coil Together.
o Remove Distributor Cap.
o Disconnect ECU trigger wire from the 6.8k ohm resistor to prevent spurious signals getting to the ECU.
o Disconnect amplifier wire from coil negative.
o Connect a 12v 21W bulb from the same amplifier wire to coil positive (12 volt supply).
o The 21W bulb acts as a substitute coil load.
o Turn ignition on and rotate distributor rotor arm back and forward against the vacuum/mechanical advance springs.
o As the toothed reluctor wheel triggers the pickup coil, the amplifier should flash the bulb.
o If bulb flashing is positive and consistent the amplifier and pickup coil are working correctly together.
o If lamp does not flash or is inconsistent/weak either the amplifier or pickup coil is faulty.
Check the pickup coil independently
o Remove the amplifier connections to the pick-up coil and measure the resistance of the distributor pickup coil for a steady value between 500 ohms to 1500 ohms on the ohm-meter. Flex the wires at the same time to test their integrity.
o Outside the above range, short or open circuit indicates a croaky pickup coil.
o By process of elimination, if the pickup coil is OK, one might conclude the amplifier is faulty but nothing is ever that simple with electronic components, so to be sure:
Test the Amplifier independently
o What follows is an elegant but slightly complex test process.
o Use a 1.5 volt pen-cell battery connected in series with a (say} 2,700 ohm resistor and two flying leads to simulate the pickup coil.
o With the coil and amplifier connected normally and the distributor pickup coil disconnected from the amplifier, connect one flying lead to one of the amplifier input connectors and touch the other flying lead intermittantly across the second amplifier input connector.
o This emulates a pulsed input thereby activating the amplifier in sympathy to generate sparks from the coil?
o Polarity of this simulation is non-critical as neither flying lead is connected to earth, only to the amplifier input connectors, and the pulsing voltage from the pen-cell via the 2700 ohm resistor acts similar to the pickup coil input without causing stress or damage to the amplifier.
o The above test can be performed with the 21 watt bulb as the coil substitute as previously described, except in that circumstance, the pick-up coil simulation will flash the bulb.
Alternatively (for even more elegance), going one step further:
o Construct a small test box complete with switch, 21 watt bulb/holder, pen-cell battery, 2700 ohm resistor, 12 volt pos/neg power connections (from a car battery), spade connectors to the amplifier, etc.
o Connect up the 12 volts power and the amplifier to the test box and flick the switch repeatedly to emulate the pulsed input from a pickup coil and see the 21 watt bulb flash in sympathy to show the amplifier is working correctly.
Other Components
o Another possible component failure will be the suppressing condenser breaking down under the back-EMF from the coil.
o Remove condenser from circuit to see if the problem disappears.
o If yes, replace the condenser.
o Almost finally! For all the previous components check the LT wiring is not corroded, broken, dodgy or otherwise failing.
o Because all the components upstream of the king lead now check out OK, if fat sparks emerge from the king lead but not at the spark plugs its time to review the downstream components to see if they are dragging down, or failing to conduct, the Hi-Tension energy.
o Rotor arm - inspect for carbon tracking, clean with WD40, smear with a trace of silicon grease to prevent moisture ingress.
o Distibutor cap - inside and outside - inspect for carbon tracking, clean with WD40, smear with a trace of silicon grease to prevent moisture ingress. Wipe completely clean and shiny, especially between the turrets.
o Plug Leads and Hi-tension connectors - inspect for breaks and contact damage, clean with WD40, smear with a trace of silicon grease to prevent moisture ingress. Wipe completely clean and shiny.
o Spark Plugs - Check for recommended type, clean and gap to correct spec, inspect for insulator damage externally and whiskering/crud between central contact and body. Clean externally to a shine.
o The above four items are "zero cost" actions. Many owners replace them all never knowing which of the components may have been faulty.
o Check by swapping is an easy process before buying replacements.
o Looking for spark tracking on a dark night generally reveals faulty hi-tension parts.
If after all the above, the intermittent failure persists, then move to the following DYNAMIC check of the ignition system.
Guaranteed Foolproof Intermittent Ignition Fault Finder.
Rig up two 4/5 watt 12 volt bulbs (or better still, 2V, 15mA LED's + 680 ohm resistors) on test leads into the cabin and connect one between coil +ve and earth and the other to coil -ve and earth. Mark the bulbs POS and NEG. Beware cables dont foul hot/moving parts.
Start the engine and observe:
POS sensing the ignition input voltage is permanently on,
AND
NEG sensing the pulsed voltage across the Ignition Amplifier flickers in sympathy with engine rpm, or is dimly lit (LED's flicker better).
Now drive the car and have a helper note what happens when the engine misbehaves.
If POS and NEG go out together there is an open circuit interruption of the 12 v feed such as a faulty wire/ignition switch,
OR
A short on the same circuit due to burned insulation.
If NEG comes full on the Ignition Amplifier (due to excess internal heat) or its associated wiring/earth has failed in open circuit mode,
OR
The pulsed input (ie Hall Effect or Reluctor) to the amplifier from the dizzy has failed or the associated wiring is faulty/shorting to earth,
OR
The Coil has failed in a short circuit mode (unlikely cos it would surely kill the amplifier methinks?)
If NEG goes out the Ignition Amplifier has temporarily failed in short circuit mode due to excess internal heat,
OR
the local wiring is shorting to earth,
OR
The coil has failed in open circuit mode due to insulation breakdown or internal heat
If POS stays lit and NEG show signs of flickering instabilitynot sympathetic with engine rpm, then the Ignition Amplifier or its connections are on the blink.
MOVING ON TO FUELLING
If no ignition faults are found and the ignition system is proven to be working correctly you will then need to move on to the fuelling system and undertake a systematic check of all the Efi components using the testing processes found in this archive
Don't overlook the fact that with intermittent faults the more likely cause is with electrical connection problems so the functional tests must be conducted as specified where the test INCLUDES the associated wiring.
Not so likely to be intermittent, but will also need to completely eliminate the possibility of an air leak into the plenum chamber, for which you will find a simple dynamic test process in the Plenum section of the mentioned archive.
If that does not expose the problem, follow this up by an elegant but slightly more complex dynamic test process designed to uncover intermittent ignition faults.
After that you can move your efforts to fuelling.
Start with this fully comprehensive component test program:
TESTNG IGNITION COMPONENTS - BACK TO BASICS
The circuit represents BOTH the system where the amplifier is mounted in an aluminium housing behind the coil AND where it is mounted on the side of the distributor. The effective electrics are the same, just the physical locations of components differ.
Be sure the earths and the wiring from the ignition switch through to the coil, distibutor and amplifier module are pretty much the same as shown.
Getting Started
o Reasons for testing the ignition system are a proven loss of sparks at the spark plugs, or weak/intermittent sparks causing misfiring.
o To proceed, separate the Low and High Tension circuits to find out immediately which circuit is faulty, then persue the fault condition in either circuit according to the results of some logical tests.
o Remove the king lead from the distributor, connect it to a good spark plug and lay the plug on the engine somewhere.
o Switch on the ignition and crank the engine.
o Is there a fat spark at the spark plug.
o If Yes - then the problems are downstream and away from the king lead at the dizzy cap, rotor arm, plug leads, plugs, or ignition timing so that is where to look - see " Other Components" (later) for checking the usual suspects, inspect, clean, substitute and only replace if faulty.
o If No - change the king lead.
o If still No - then the problems are upstream from the king lead and towards the coil, amplifier, distributor innards or their local connections all the way back to the ignition switch.
Testing the Low Tension Side Voltage Feed
o Switch on the ignition and use a multimeter to verify there are 12 volts at coil positive.
o If No - find out why, by checking the circuit between coil positive and the ignition switch and beyond, all the way back to the battery if necessary, for corroded or loose/broken connections.
o If Yes - dont take it for granted, waggle local wiring and toggle the ignition switch a few time to ensure the voltage is reliable, even using a bright lamp to check the wiring can supply a load.
Test the coil independently
o Disconnect the wire from coil negative to the amplifier.
o Turn ignition on, and strike coil negative to earth with a flying lead to see how good is the king lead spark.
o If sparks are absent/poor/weak and +12 volts is still present at coil positive then the coil is prime suspect for inspection/replacement.
o If sparks are fat/healthy then coil must be OK, so look for amplifier/pickup coil problems.
Test the Amplifier and Distributor Pickup Coil Together.
o Remove Distributor Cap.
o Disconnect ECU trigger wire from the 6.8k ohm resistor to prevent spurious signals getting to the ECU.
o Disconnect amplifier wire from coil negative.
o Connect a 12v 21W bulb from the same amplifier wire to coil positive (12 volt supply).
o The 21W bulb acts as a substitute coil load.
o Turn ignition on and rotate distributor rotor arm back and forward against the vacuum/mechanical advance springs.
o As the toothed reluctor wheel triggers the pickup coil, the amplifier should flash the bulb.
o If bulb flashing is positive and consistent the amplifier and pickup coil are working correctly together.
o If lamp does not flash or is inconsistent/weak either the amplifier or pickup coil is faulty.
Check the pickup coil independently
o Remove the amplifier connections to the pick-up coil and measure the resistance of the distributor pickup coil for a steady value between 500 ohms to 1500 ohms on the ohm-meter. Flex the wires at the same time to test their integrity.
o Outside the above range, short or open circuit indicates a croaky pickup coil.
o By process of elimination, if the pickup coil is OK, one might conclude the amplifier is faulty but nothing is ever that simple with electronic components, so to be sure:
Test the Amplifier independently
o What follows is an elegant but slightly complex test process.
o Use a 1.5 volt pen-cell battery connected in series with a (say} 2,700 ohm resistor and two flying leads to simulate the pickup coil.
o With the coil and amplifier connected normally and the distributor pickup coil disconnected from the amplifier, connect one flying lead to one of the amplifier input connectors and touch the other flying lead intermittantly across the second amplifier input connector.
o This emulates a pulsed input thereby activating the amplifier in sympathy to generate sparks from the coil?
o Polarity of this simulation is non-critical as neither flying lead is connected to earth, only to the amplifier input connectors, and the pulsing voltage from the pen-cell via the 2700 ohm resistor acts similar to the pickup coil input without causing stress or damage to the amplifier.
o The above test can be performed with the 21 watt bulb as the coil substitute as previously described, except in that circumstance, the pick-up coil simulation will flash the bulb.
Alternatively (for even more elegance), going one step further:
o Construct a small test box complete with switch, 21 watt bulb/holder, pen-cell battery, 2700 ohm resistor, 12 volt pos/neg power connections (from a car battery), spade connectors to the amplifier, etc.
o Connect up the 12 volts power and the amplifier to the test box and flick the switch repeatedly to emulate the pulsed input from a pickup coil and see the 21 watt bulb flash in sympathy to show the amplifier is working correctly.
Other Components
o Another possible component failure will be the suppressing condenser breaking down under the back-EMF from the coil.
o Remove condenser from circuit to see if the problem disappears.
o If yes, replace the condenser.
o Almost finally! For all the previous components check the LT wiring is not corroded, broken, dodgy or otherwise failing.
o Because all the components upstream of the king lead now check out OK, if fat sparks emerge from the king lead but not at the spark plugs its time to review the downstream components to see if they are dragging down, or failing to conduct, the Hi-Tension energy.
o Rotor arm - inspect for carbon tracking, clean with WD40, smear with a trace of silicon grease to prevent moisture ingress.
o Distibutor cap - inside and outside - inspect for carbon tracking, clean with WD40, smear with a trace of silicon grease to prevent moisture ingress. Wipe completely clean and shiny, especially between the turrets.
o Plug Leads and Hi-tension connectors - inspect for breaks and contact damage, clean with WD40, smear with a trace of silicon grease to prevent moisture ingress. Wipe completely clean and shiny.
o Spark Plugs - Check for recommended type, clean and gap to correct spec, inspect for insulator damage externally and whiskering/crud between central contact and body. Clean externally to a shine.
o The above four items are "zero cost" actions. Many owners replace them all never knowing which of the components may have been faulty.
o Check by swapping is an easy process before buying replacements.
o Looking for spark tracking on a dark night generally reveals faulty hi-tension parts.
If after all the above, the intermittent failure persists, then move to the following DYNAMIC check of the ignition system.
Guaranteed Foolproof Intermittent Ignition Fault Finder.
Rig up two 4/5 watt 12 volt bulbs (or better still, 2V, 15mA LED's + 680 ohm resistors) on test leads into the cabin and connect one between coil +ve and earth and the other to coil -ve and earth. Mark the bulbs POS and NEG. Beware cables dont foul hot/moving parts.
Start the engine and observe:
POS sensing the ignition input voltage is permanently on,
AND
NEG sensing the pulsed voltage across the Ignition Amplifier flickers in sympathy with engine rpm, or is dimly lit (LED's flicker better).
Now drive the car and have a helper note what happens when the engine misbehaves.
If POS and NEG go out together there is an open circuit interruption of the 12 v feed such as a faulty wire/ignition switch,
OR
A short on the same circuit due to burned insulation.
If NEG comes full on the Ignition Amplifier (due to excess internal heat) or its associated wiring/earth has failed in open circuit mode,
OR
The pulsed input (ie Hall Effect or Reluctor) to the amplifier from the dizzy has failed or the associated wiring is faulty/shorting to earth,
OR
The Coil has failed in a short circuit mode (unlikely cos it would surely kill the amplifier methinks?)
If NEG goes out the Ignition Amplifier has temporarily failed in short circuit mode due to excess internal heat,
OR
the local wiring is shorting to earth,
OR
The coil has failed in open circuit mode due to insulation breakdown or internal heat
If POS stays lit and NEG show signs of flickering instabilitynot sympathetic with engine rpm, then the Ignition Amplifier or its connections are on the blink.
MOVING ON TO FUELLING
If no ignition faults are found and the ignition system is proven to be working correctly you will then need to move on to the fuelling system and undertake a systematic check of all the Efi components using the testing processes found in this archive
Don't overlook the fact that with intermittent faults the more likely cause is with electrical connection problems so the functional tests must be conducted as specified where the test INCLUDES the associated wiring.
Not so likely to be intermittent, but will also need to completely eliminate the possibility of an air leak into the plenum chamber, for which you will find a simple dynamic test process in the Plenum section of the mentioned archive.
OK, had another play with it. definitely temperature related, started first time and ran well until close to normal temperature, then started to play up.
Sparks are good and strong, and constant! No sign of any tracking in dizzy cap and leads don't seem to be breaking down!
Looks like fuelling or a duff sensor!
Sparks are good and strong, and constant! No sign of any tracking in dizzy cap and leads don't seem to be breaking down!
Looks like fuelling or a duff sensor!
Portable oscilloscope on the ignition trigger input to the ECU whilst driving around would be the fast way to prove/disprove the ignition side of things. If the ECU can't see a decent signal the fuelling won't work; once you know it's definitely fuel- or spark-related you're almost home and dry 
PoleDriver said:
Sparks are good and strong, and constant! No sign of any tracking in dizzy cap and leads don't seem to be breaking down!
Looks like fuelling or a duff sensor
You should put up a smiley because you have now eliminated half of the potential issues by reporting good strong sparks. Did something change to get to that state?Looks like fuelling or a duff sensor
Presumably they are good and strong when cold. Are the sparks good and strong when the engine is hot when the problem actually occurs. You didn't say!
Assuming Yes! and moving to fuelling, the best self help clue you could provide would be the state of the spark plugs WHEN THE FAULT HAS OCCURRED.
One plug from each bank would be a good indicator.
If you find them to be black and/or wet, then its deffo fuelling and being too rich - you follow?
You mention that it may be a sensor, well yes - and you also say in the first post that you replaced two of them, CTS and throt pot - but suppose their local connections are dodgy - then the replacement components will display the same issues, so you have to test the components in relation to their local connections. random component replacement never finds a connection prob.
FYI, 80% of all RV8 Efi faults are due to connection probs and rogue air leaks so for a fuelling issue, that is the place to begin.
The foregoing point about connections is one of the reasons why I built a splitter box, so as to be able to test components and their outputs, with the system working on the vehicle.
Repeated plugging and unplugging of that design of connector invariably weakens the grip of the spring terminals within them; you can get replacement terminals (and some of the housings) from Vehicle Wiring Products.
Repeated plugging and unplugging of that design of connector invariably weakens the grip of the spring terminals within them; you can get replacement terminals (and some of the housings) from Vehicle Wiring Products.
Any connections which looked 'iffy' have been replaced/remade.
An interesting thing I noticed, which may or not be a clue... I totally shut off the major vacuum pipe going to the idle valve while the engine was running rough. It made no difference when ticking over or 'blipping' the throttle, surely this would make matters worse? have I found the problem?
An interesting thing I noticed, which may or not be a clue... I totally shut off the major vacuum pipe going to the idle valve while the engine was running rough. It made no difference when ticking over or 'blipping' the throttle, surely this would make matters worse? have I found the problem?
I had the same problem all last year with my 420SE. Miss fire, poor throttle response and dumping fuel into the engine. One day it would be fine the other a no go. Found later to be a wirring fault throughout the car. Ive gone for the cheap option, got rid of the fuel injection system and we are fitting a Holley 600CFM Carb, should get rid of all problems, back to basics!!!
Gassing Station | Wedges | Top of Page | What's New | My Stuff