My missfire...running out of ideas ?????

[maston]

Hi All,
Well the 390 drove lovely to the meet on Sunday but then drove like a bag of nails on the drive home later.
It has now decided to missfire throughout the whole rev range ?

Would kn*ckered injectors cause this problem ?
I do know that I have at least 1 leaking injector (diagnosed last year that when the engine is switched off the fuel pressure immediately drops to zero) and now I am wondering if there is a blocked injector to add to the problems ???

Mark noticed how rich it was when it was idling at the diner, fuel was spitting out.

I have tried swopping the ecu, afm, power resistor with known good ones, all to no avail.
The plugs are only a couple of months old.
The leads are ok.

The cts is good and so is the throttle pot and the the throttle pot tract.

Getting increasingly p*ssed off with the thing and seriously considering p/xing with a boxster s

Please help me save my wedge

[mrzigazaga]

Ian...As i believe it..Although i could be wrong...If the fuel pressure was checked at the cold start and is falling away then it might be a failing Fuel pressure regulator...I have a spare but its set to a 3.5ltr and i think you need more pressure for the 390se..If not then you are more than welcome to try it mate....I can post it out once confirmed...Ziga

[MPoxon]

I might be a long shot but FlipFlop had a misfire issue with his Griff which seemed to be going on for years. Like you after changing lots of bits over David Gerald troubleshooted the issue down to the engine earth strap. Fitted a new one and no more misfire.

Only other thing to check would be that you have got a proper lucas rotor arm and cap. The pattern parts can cause misfire issues.

[maston]

Thanks Mark but I have tried a known good standard regulator with no difference.
However , maybe this one (I bought a second hand fuel rail that came with injectors and the regulator) is set to the wrong pressure (it came off of a Land Rover I think)
I'll speak to you later mate

[maston]

MPoxon said:

I might be a long shot but FlipFlop had a misfire issue with his Griff which seemed to be going on for years. Like you after changing lots of bits over David Gerald troubleshooted the issue down to the engine earth strap. Fitted a new one and no more misfire.

Only other thing to check would be that you have got a proper lucas rotor arm and cap. The pattern parts can cause misfire issues.

Thanks for your reply.
I have recently installed a new earth strap too and the rotor arm and dizzy is a mallory set up, again all new but thanks anyway. Will check ALL the earths again

[Jack Valiant]

Ian did you not get my email fella about things to check fella? Echo the points re the earth straps .. seem to remember we did clean them off when I came round last time. Most of the bigger capacity RV8 motors will run rich at warm start up. What plugs did you end up putting in the motor fella? I have a set of Iridium ones you can try to eliminate from the issue.

Chris

[Wedg1e]

Injectors and fuel pressure regs don't tend to fail in a way that generates a random misfire - Ian said it was running fine going out and then badly coming home.

I'd be hanging a 'scope on the injector trigger outputs from the ECU to see whether it's missing because the ECU is telling it to, whether the ignition amp isn't triggering the ECU properly or whether the fuel pump is stuttering... and then widening the search.
No harm in checking the engine/ chassis/ battery/ wiring loom earths first though.

[maston]

Jack Valiant said:

Ian did you not get my email fella about things to check fella? Echo the points re the earth straps .. seem to remember we did clean them off when I came round last time. Most of the bigger capacity RV8 motors will run rich at warm start up. What plugs did you end up putting in the motor fella? I have a set of Iridium ones you can try to eliminate from the issue.

Chris

Thanks Chris, will bear that in mind.

[maston]

Wedg1e said:

I'd be hanging a 'scope on the injector trigger outputs from the ECU to see whether it's missing because the ECU is telling it to, whether the ignition amp isn't triggering the ECU properly or whether the fuel pump is stuttering... and then widening the search.
.

Thanks Ian, not sure what a 'scope is though and how I actually check ?
Also, don't know if it makes any difference but I do not have an ignition amp (mallory set up)?
Regards
Ian

Edited by maston on Monday 17th February 18:39

[sunbeam alpine]

Could it be the fuel pump? Don't have a TVR but spent ages looking at electrical problems on one of my cars, only to find it was the pump.

[MrPicky]

Check the connection to the resistor pack on the inner wing, it will seem like injector problems but it isn't.

Russ

[V8 Fettler]

OP, you should be pleased it's now a constant misfire. should make it easier to resolve!

As a start, get the car warm, disconnect the throttle pot and see if the misfire goes away. Leave it disconnected if the fault persists, disconnect the coolant temp sensor and bridge the leads with a a 200ohm resistor. A warm car should run OK with no misfires with the throttle pot disconnected and a 200ohm resistor in place of the coolant temp sensor.

Have you checked fuel rail pressure?

[matt-man]

Ian-have you got spark, fuel and compression on every cylinder??

You need to know the basics before you keep searching blind.

As I've said before, my random misfire which I had for about 2 years before I found it was a slightly damaged valve which would intermittently stick so I lost compression on one cylinder.

You need to check this...a compression tester is really cheap and a must for the garage

[wuckfitracing]

My 2p worth. Was the battery fully charged before you left. Have you checked voltage output of the alternator. If the battery starts to die it will cause a misfire across all rev range.

[adam quantrill]

Good point and as all Wedges have a voltmeter that's a very quick check - do it with all the ancillaries turned off.

[Wedg1e]

I had my alternator brushes wear out a few years back; I was at the g/f's place nearly 70 miles from home.
I borrowed a neighbour's charger and got a couple of hours' charge in the battery then set off. Essentially it was Russian Roulette but I had no breakdown cover and it was a Sunday so no chance of getting a brush set for the alternator and no tools with me to fit them anyway!
The first 20 miles or so went quite smoothly, couldn't really tell there was a problem apart from the gradually-sinking voltmeter. I had everything electrical turned off, only indicated when absolutely necessary.
Then just as I joined the A1, the car stuttered and began to lose power. I headed for the hard shoulder, racking my brains for who I could call for a tow before the Plod arrived and arranged something for me!
With yards to go before I stopped, the engine suddenly picked-up again. Bu99er it, I thought, and pulled back out into traffic. Half a mile up the road, it happened again. I discovered that if I turned the ignition off and coasted with the clutch held down, then turned ignition back on and dumped the clutch, the engine would restart and run as normal... for another half mile or so.
Unbelievably, I managed over 40 miles back home in this fashion. Towards the end I was down to less than 30mph but the car refused to die. The Tees flyover was a bit hair-raising at that speed but the alternative would have meant crawling through the town and risking the engine dying at a traffic light.
With a new set of brushes and a recharge, normal service was resumed and the same battery is on the car still. I can understand the injection ECU not minding a drop in voltage, after all it's internally regulated to a lower voltage anyway but the fuel pump draws loads of current and should have pulled the battery through the floor.
So I'm not convinced a duff battery would give the symptoms stated; in theory if the alternator's working fine thee should be more than enough current available for the fuel pump and injection... but who knows?

[MPoxon]

maston said:

Thanks for your reply.
I have recently installed a new earth strap too and the rotor arm and dizzy is a mallory set up, again all new but thanks anyway. Will check ALL the earths again

Sorry that is the extent of my limited knowledge. I am sure you will get her back to health soon, just keep trying and don't give up. You would regret selling for a Boxster.

I had a similar issue on mine a long while back fortunately the misfire eventually turned into a full failure and was easy to troubleshoot (for the garage that is). Turned out to be a short on one of the earths on the loom. I was very close to binning the whole ECU and loom and starting fresh out of despiration but glad I managed to get it sorted with the original system. I too had changed many parts with no result, most of my ignition system is like Trigger's Broom!

[honestjohntoo]

maston said:

I do know that I have at least 1 leaking injector (diagnosed last year that when the engine is switched off the fuel pressure immediately drops to zero) and now I am wondering if there is a blocked injector to add to the problems ???

Mark noticed how rich it was when it was idling at the diner, fuel was spitting out.


Getting increasingly p*ssed off with the thing

From the above and reading previous related threads, there is quite a lot to go on!

Investigate and fix the signs/symptoms already identified.

ie

- leaking injector

- falling fuel pressure

- spitting fuel

Suggestions

• inspect each spark plug to pin-point the possible culprit injector(s).

• wet/sooty plug = leaking injector

• four wet plugs on same bank = faulty ECU

• cooler exhaust manifold/pipe = blocked injector (or missing spark) on that cylinder

• test the FPR for variable fuel pressure when idling and pulsing throttle

• fuel pressure varying between 26 and 36 psi on standard 3.5 or possibly 29 and 39 psi on larger engines

• typically 10 psi differential

If none of the above yield a solution then methinks it would be prudent to drain the swamp (when up to one's ass in alligators).

• Read and apply the 15 point health plan found here here:

• for fuller understanding of the Flapper Efi System, obtain/study the 'Efi Operations Manual'

Moving On

• your 'all new' Mallory ignition system will not be immune to loose low tension connections

• check and double check all the ignition wiring from the ignition switch all the way thro to dizzy, coil and all earth's.

• the same treatment is valid for the particularly vulnerable and troublesome Efi wiring loom connections.

• check for a clean Efi system earth connection behind and below the LH Rocker cover

If (after draining the swamp) you still have miss-fire problems - based upon any new symptoms you can report, I'm sure I can do further analysis.

[HOTTY]

Hi Ian

Hopefully you find you fault quickly.

My only running fault on the 400 was a faulty earth.

Wish i could offered more (matches and a full petrol can!)

keep your chin up

hotty

[superwedge]

these cars need a good battery,so make sure it spot on,