ECU Relay Buzzing
Discussion
Hi,
Recently joined the world of TVR with a 96 Chimaera 500. Not too far into the relationship, we had a disagreement and both ended up in a ditch! This resulted in damage to the off-side front bodywork, Carbon Can, headlight etc. but no damage to chassis (sigh of relief). The car wouldn't start after the accident, had to tow him home.
Before I take the car to get the body work repaired, I want to get him started, so…
After fitting a new carbon can, resetting the inertia switch, charging the battery (he'd been sitting for a while before I had the chance to do anything), checked all fluids and levels I tried to start him.
Switched the immobiliser off, turn the key to position 2. This causes the ECU relay - metal relay in the passenger footwell on the black connector - to start buzzing!
I've checked the relays, I swapped them both out in turn with a new spare. Nothing! I've checked the voltage across both relays (pins 85 and 86), this should be 12v (?) but is in fact 4.8v. There is no voltage across the fuel pump and it doesn't prime.
Is there a re-set feature for the roll over valve in the boot? The bible mentions that this sometimes trips in an accident, but doesn't say whether it has a reset switch?
Anyone had any similar experiences? Any Ideas apart from get in auto sparky?
Recently joined the world of TVR with a 96 Chimaera 500. Not too far into the relationship, we had a disagreement and both ended up in a ditch! This resulted in damage to the off-side front bodywork, Carbon Can, headlight etc. but no damage to chassis (sigh of relief). The car wouldn't start after the accident, had to tow him home.
Before I take the car to get the body work repaired, I want to get him started, so…
After fitting a new carbon can, resetting the inertia switch, charging the battery (he'd been sitting for a while before I had the chance to do anything), checked all fluids and levels I tried to start him.
Switched the immobiliser off, turn the key to position 2. This causes the ECU relay - metal relay in the passenger footwell on the black connector - to start buzzing!
I've checked the relays, I swapped them both out in turn with a new spare. Nothing! I've checked the voltage across both relays (pins 85 and 86), this should be 12v (?) but is in fact 4.8v. There is no voltage across the fuel pump and it doesn't prime.
Is there a re-set feature for the roll over valve in the boot? The bible mentions that this sometimes trips in an accident, but doesn't say whether it has a reset switch?
Anyone had any similar experiences? Any Ideas apart from get in auto sparky?
The battery is fully charged, I took it out and topped up the charge and put it back, made sure all connections are secure, which they are! All fuses on the board seem to be fine (painstakingly took them all out to check them, even ran a continuity test across the important ones, ecu, ignition...)
Same problem still exists. Help!
Same problem still exists. Help!
Does the feed run through the immobiliser,if so it may be worth by passing it to count it out.I wouldnt have thought it was a cut out as there would be "0" voltage across the pins.A high resistance short through a trapped wire could give a similar problem (and a bigger one when it eventually shorts dead).CIs it possible to trace the wire feed back to its supply with a continuity tester??
Edited by clarenceboddiger on Saturday 5th August 07:33
The fuel pump will not have a voltage across it until the relay is working properly, so it's not likely there's a problem there. Having just 4.8V across the main relay and fuel pump relay means one of two things: either the supply is at 4.8V, or the ground connection is not at 0V.
The main relay has a permanent 12V supply to terminal 86, the fuel pump relay has a supply switched by the ignition switch. Terminal 85 (ground) is controlled by the ECU on both relays, on different pins on the ECU (pin 12, main relay, pin 16, fuel pump relay). Both are at 4.8V so perhaps there's a poor earth connection somewhere? Has there been any water ingress since visiting the ditch? The ECU should be grounded on pins 4, 14, 27 and 40. Checking for continuity between here and the battery earth post might be a good place to start.
The main relay has a permanent 12V supply to terminal 86, the fuel pump relay has a supply switched by the ignition switch. Terminal 85 (ground) is controlled by the ECU on both relays, on different pins on the ECU (pin 12, main relay, pin 16, fuel pump relay). Both are at 4.8V so perhaps there's a poor earth connection somewhere? Has there been any water ingress since visiting the ditch? The ECU should be grounded on pins 4, 14, 27 and 40. Checking for continuity between here and the battery earth post might be a good place to start.
Some random thoughts in no particular order.
It sounds as if you're comfortable doing basic electrical tests and that's all it will take to track the problem down.
Is the battery holding up at 12v or more when you get this problem?
You need to know whether the buzzing relay is powering the ECU or the fuel pump in order to diagnose it. If you take the relay out and short across terminals 30/87 on the relay socket with a fused wire this will similate the relay in the closed position. If the pump runs you know this is the socket for the fuel pump + lambda heater relay; the other one then is the main power relay. If the fuel pump doesn't run when you do this for either socket then you have a more fundamental problem.
Are you measuring the voltage across 85/86 with the relay present? If it's buzzing it's likely that the voltage is fluctuating rapidly and what you're seeing may just be an average. So e.g. an indicated 4v drop might actually by an 8v drop.
The -ve side of the coil for the fuel pump relay is pulled down by the ECU and it doesn't get pulled down quite as far as 0v so you won't see 12v here. But the relay should trip quite happily with 8v across it. I suggest you check the voltage of each side of the relay coil i.e. between battery -ve and the coil -ve and between battery +ve and the coil +ve. If the voltage drop is on the +ve side you have a wiring fault or dodgy immobiliser. If it's on the -ve side then a couple of volts is normal but anything more than that indicates a dodgy ECU earth, wiring fault, or hardware failure within the ECU. The ECU is pretty rugged but if it's been smacked there's always a chance that it has been damaged. They suffer from spontaneous dry joints at the best of times.
Hope this helps.
It sounds as if you're comfortable doing basic electrical tests and that's all it will take to track the problem down.
Is the battery holding up at 12v or more when you get this problem?
You need to know whether the buzzing relay is powering the ECU or the fuel pump in order to diagnose it. If you take the relay out and short across terminals 30/87 on the relay socket with a fused wire this will similate the relay in the closed position. If the pump runs you know this is the socket for the fuel pump + lambda heater relay; the other one then is the main power relay. If the fuel pump doesn't run when you do this for either socket then you have a more fundamental problem.
Are you measuring the voltage across 85/86 with the relay present? If it's buzzing it's likely that the voltage is fluctuating rapidly and what you're seeing may just be an average. So e.g. an indicated 4v drop might actually by an 8v drop.
The -ve side of the coil for the fuel pump relay is pulled down by the ECU and it doesn't get pulled down quite as far as 0v so you won't see 12v here. But the relay should trip quite happily with 8v across it. I suggest you check the voltage of each side of the relay coil i.e. between battery -ve and the coil -ve and between battery +ve and the coil +ve. If the voltage drop is on the +ve side you have a wiring fault or dodgy immobiliser. If it's on the -ve side then a couple of volts is normal but anything more than that indicates a dodgy ECU earth, wiring fault, or hardware failure within the ECU. The ECU is pretty rugged but if it's been smacked there's always a chance that it has been damaged. They suffer from spontaneous dry joints at the best of times.
Hope this helps.
OK, the plot thickens...
Took out the battery, it had lost a lot of charge since being topped up last week! Charged it an put it back.
Took out the suspect relay, tested voltage across pins 85 and 86 of the socket, reading of 4.8v! Took a direct feed from the -ve terminal of the battery, tested the voltage between this and pin 86. 12v! So by my (somewhat worn out) powers of deduction, I think I have a problem with an earth connection somewhere between the -ve terminal on the battery and the -ve connection on the main relay. (It is the main ECU relay as it has a permanant voltage across it).
There may have been water ingress at one point as he sat in a storage yard for a couple of months while I fought wih the insurance people! - I suspect this might be the issue, but where?!?
Thanks for the support so far, any more suggestions? When I get another chance I'll trace it back a step to the ECU...
Took out the battery, it had lost a lot of charge since being topped up last week! Charged it an put it back.
Took out the suspect relay, tested voltage across pins 85 and 86 of the socket, reading of 4.8v! Took a direct feed from the -ve terminal of the battery, tested the voltage between this and pin 86. 12v! So by my (somewhat worn out) powers of deduction, I think I have a problem with an earth connection somewhere between the -ve terminal on the battery and the -ve connection on the main relay. (It is the main ECU relay as it has a permanant voltage across it).
There may have been water ingress at one point as he sat in a storage yard for a couple of months while I fought wih the insurance people! - I suspect this might be the issue, but where?!?
Thanks for the support so far, any more suggestions? When I get another chance I'll trace it back a step to the ECU...
Does sound rather like a poor earth on the ECU, although it's possible it is a wiring fault or even a fault inside the ECU itself. Try the ECU earth first though, it's the easiest to fix. You should find two earth wires bolted to the engine in the vicinity of the rear nearside mount of the fuel rail.
One click, two clicks, ah, the reassuring sound of the fuel pump priming. No Buzzing. One last turn of the key and the Sgt Major roars into action, that fantastic V8 rumble that we all know and love!
These are the moments leading up to my moment of euphoria and general dancing round the driveway!
So how did I get here? After spending hours looking for, finding, cleaning earths, recharging battery... I called in an electrician! He spent 5 minutes doing all the tests that I had previously done (thanks guys), then he took the ECU out, removed the screws and pointed to the blackened area around the earth contacts on the PCB. Turns out the Chim had brain damage, that's why the relays were buzzing, that's why he would turn over! Suspected cause is someone (Insurance comp, salvage yard?) trying to jump start after a flat battery (stupid meta alarm!) and either using a high voltage started unit or reversing the batt terminals(!).
Amway, after spending a bit of time with the (ECU) Doctor, the ECU arrived back with a clean bill of health. Plugged it in, reconnected the battery and turned the key...
Thanks everyone for your words of advice, all that remains now is to get the bodywork done, minor service, hand wash...
If anyone has any electrical issues and suspects their ECU to be sick, the ECUDoctor in Plymouth runs an excellent service and if they can fix my fried ECU, shouldn't have many problems with other ailments!
These are the moments leading up to my moment of euphoria and general dancing round the driveway!
So how did I get here? After spending hours looking for, finding, cleaning earths, recharging battery... I called in an electrician! He spent 5 minutes doing all the tests that I had previously done (thanks guys), then he took the ECU out, removed the screws and pointed to the blackened area around the earth contacts on the PCB. Turns out the Chim had brain damage, that's why the relays were buzzing, that's why he would turn over! Suspected cause is someone (Insurance comp, salvage yard?) trying to jump start after a flat battery (stupid meta alarm!) and either using a high voltage started unit or reversing the batt terminals(!).
Amway, after spending a bit of time with the (ECU) Doctor, the ECU arrived back with a clean bill of health. Plugged it in, reconnected the battery and turned the key...
Thanks everyone for your words of advice, all that remains now is to get the bodywork done, minor service, hand wash...
If anyone has any electrical issues and suspects their ECU to be sick, the ECUDoctor in Plymouth runs an excellent service and if they can fix my fried ECU, shouldn't have many problems with other ailments!
Hi Chaps, where is the Ecu relay please as i have to try it's replacement as my intermittant fault with the ecu seems to be still bugging me! I took my beloved to a diagnostics centre two days ago and the ecu was not showing any faults at all (No faults at all even on engine)of course the fault didn't re-appear while i was in the garage despite me turning the ignition on and off, with the rain bucketing outside (perfect conditions!!)A lot of what Green v8s has written here looks highly relevant to my problem but my Mandarin chinese is not all that clever!! Any ideas please, gratefully recieved
There are two relays in the passenger footwell near the battery case, both in an aluminium casing on loose spurs off the wiring loom. One is the ECU relay, the other is for the fuel pump. They are interchangeable as they are identical. If you're having a problem try swapping them round.
www.pistonheads.com/sales/103740.htm
May be hiring out ECUs soon as well as readers so people can quickly see if their ECU is misbehaving by plugging in a replacement.
May be hiring out ECUs soon as well as readers so people can quickly see if their ECU is misbehaving by plugging in a replacement.
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