Rough running engine
Discussion
Hi Folks,
Only just managed to get home.
Whilst on a run, engine started misfiring, not just one or two but all cylinders stopped firing very briefly. Then back to running fine again.
This happened about once a minute to start with but the intervals started getting shorter then just like really rough running. Ran into a long traffic jam which was a nightmare. Had to brake with heel and keep throttle pressed with toe to stop it stalling. Revs jumping between near stall and around 2500rpm as it ran then cut out repeatedly.
Sometimes wouldn't idle and then other times fine.
Gradually getting worse and worse. By time I reached home, really rough running.
Shut down then turned ignition ON, got the fuel pump whine and click off then a longer wheezing/buzzing noise from the fuel tank area. Opened the fuel cap and got a big rush of air. Think it was expelling air rather than drawing it in but could be wrong.
What causes the tank to pressurise? Is it related to the carbon can in the front wing?
After expelling the air, the engine seems to run better but I also fiddled around in the passenger footwell as I think I have a poor ECU connection somewhere so that could have resolved it. Can tank pressure cause really rough running?
Only just managed to get home.
Whilst on a run, engine started misfiring, not just one or two but all cylinders stopped firing very briefly. Then back to running fine again.
This happened about once a minute to start with but the intervals started getting shorter then just like really rough running. Ran into a long traffic jam which was a nightmare. Had to brake with heel and keep throttle pressed with toe to stop it stalling. Revs jumping between near stall and around 2500rpm as it ran then cut out repeatedly.
Sometimes wouldn't idle and then other times fine.
Gradually getting worse and worse. By time I reached home, really rough running.
Shut down then turned ignition ON, got the fuel pump whine and click off then a longer wheezing/buzzing noise from the fuel tank area. Opened the fuel cap and got a big rush of air. Think it was expelling air rather than drawing it in but could be wrong.
What causes the tank to pressurise? Is it related to the carbon can in the front wing?
After expelling the air, the engine seems to run better but I also fiddled around in the passenger footwell as I think I have a poor ECU connection somewhere so that could have resolved it. Can tank pressure cause really rough running?
Edited by taylormj4 on Wednesday 8th April 18:41
Belle427 said:
Fuel tank vent system which includes the carbon can.
First place to start is at the vent hose at the rear of the car and the rollover valve, these can become blocked allowing tank pressure to build.
Difficult to access though.
Can cause rough running.
Thanks Belle,First place to start is at the vent hose at the rear of the car and the rollover valve, these can become blocked allowing tank pressure to build.
Difficult to access though.
Can cause rough running.
Are these located in the boot or under the car near the pump / filter area please?
In the boot behind tank.
Similar problem here on a Griff but the same thing.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Similar problem here on a Griff but the same thing.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Belle427 said:
In the boot behind tank.
Similar problem here on a Griff but the same thing.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Nice, thanks Belle. I used to get the BOING from the tank years ago but not recently. Often have a bit of pressure relief when opening the filler so even if this didn't cause the rough running, it needs sorting. Another one for the list !Similar problem here on a Griff but the same thing.
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Update:
Did some fault finding over the weekend.
Put Rovergauge on: no fault codes, and now engine seems to be running OK/
However, I then, by a bit of luck found a fault.
I had the IGN on but engine off and whilst I was moving wires around I moved the wires covered by the sticker around, just to try to read the text on the sticker and the fuel pump suddenly primed. Hang on a minute.....that means the IGN just went off and came back on again, at least as far as the ECU was concerned !
This could be repeated by moving the wires around, i.e. fuel pump priming.
It is a connector off the main loom, near the ECU, with what I thought was the tune resistor (a group of wires covered in a yellow sticker) as shown below:
Removed the sticker and found it was actually just covering three black (presumably negative) wires that loop in and out of this connector. No tune resistor as I had thought it was covering. The wires all look in good condition so suspected the connector. Did my best to clean the exposed pins. Tried to remove the pins from the connector block to get better access for cleaning. Opened a gate on the back of the connector block but the pins still didn't want to come out.
So looked like a high resistance joint. A bad joint would also be why these wires were getting warm maybe - see my other thread:
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Testing across pins on the male connector (end with the looped wires) was certainly indicating poor contact between my multimeter probes and the pins. Was getting intermittent contact.
Still, all cleaned and put back together and engine seems to be running OK.
Not sure if this has resolved the rough running yet, need to do some road tests but it certainly won't have been helping having the ECU and fuel pump cutting in and out due to poor connections in this block.
Does anyone know what this block is for? Looks like it connects to something else that is not used on the TVR, e.g. an auto gearbox and they have just connected some of the pins out.
Tried finding the block in Steve Heath's book but can't find it on the wiring diagrams. Wondering if these wires are just in the circuit to the fuel pump and maybe ignition or if they are also in the live feed to the ECU?
Would be great if this also cured the low volts at the solenoid, which is another problem I need to resolve, that I thought was the 'hot start' issue but more recently became a 'cold start' issue too
The engine certainly fired up super quick when I tested it, like caught me by surprise quick! 
Did some fault finding over the weekend.
Put Rovergauge on: no fault codes, and now engine seems to be running OK/
However, I then, by a bit of luck found a fault.
I had the IGN on but engine off and whilst I was moving wires around I moved the wires covered by the sticker around, just to try to read the text on the sticker and the fuel pump suddenly primed. Hang on a minute.....that means the IGN just went off and came back on again, at least as far as the ECU was concerned !
This could be repeated by moving the wires around, i.e. fuel pump priming.
It is a connector off the main loom, near the ECU, with what I thought was the tune resistor (a group of wires covered in a yellow sticker) as shown below:
Removed the sticker and found it was actually just covering three black (presumably negative) wires that loop in and out of this connector. No tune resistor as I had thought it was covering. The wires all look in good condition so suspected the connector. Did my best to clean the exposed pins. Tried to remove the pins from the connector block to get better access for cleaning. Opened a gate on the back of the connector block but the pins still didn't want to come out.
So looked like a high resistance joint. A bad joint would also be why these wires were getting warm maybe - see my other thread:
https://www.pistonheads.com/gassing/topic.asp?h=0&...
Testing across pins on the male connector (end with the looped wires) was certainly indicating poor contact between my multimeter probes and the pins. Was getting intermittent contact.
Still, all cleaned and put back together and engine seems to be running OK.
Not sure if this has resolved the rough running yet, need to do some road tests but it certainly won't have been helping having the ECU and fuel pump cutting in and out due to poor connections in this block.
Does anyone know what this block is for? Looks like it connects to something else that is not used on the TVR, e.g. an auto gearbox and they have just connected some of the pins out.
Tried finding the block in Steve Heath's book but can't find it on the wiring diagrams. Wondering if these wires are just in the circuit to the fuel pump and maybe ignition or if they are also in the live feed to the ECU?
Would be great if this also cured the low volts at the solenoid, which is another problem I need to resolve, that I thought was the 'hot start' issue but more recently became a 'cold start' issue too
The engine certainly fired up super quick when I tested it, like caught me by surprise quick! Edited by taylormj4 on Monday 13th April 14:40
Its known as the loopback connector, think it was designed to add another immobiliser system but not used.
Contains wiring from starter solenoid and fuel pump but Im not sure if the ignition circuit goes thorough it too.
You could remove it if it gives problems you cant resolve, you just need to join the appropriate wires together that are looped.
Does it have 3 pairs of wires?
Contains wiring from starter solenoid and fuel pump but Im not sure if the ignition circuit goes thorough it too.
You could remove it if it gives problems you cant resolve, you just need to join the appropriate wires together that are looped.
Does it have 3 pairs of wires?
Edited by Belle427 on Monday 13th April 16:46
Belle427 said:
Its known as the loopback connector, think it was designed to add another immobiliser system but not used.
Contains wiring from starter solenoid and fuel pump but Im not sure if the ignition circuit goes thorough it too.
You could remove it if it gives problems you cant resolve, you just need to join the appropriate wires together that are looped.
Does it have 3 pairs of wires?
Yes, three looped wires making six connections in the connector blocks.Contains wiring from starter solenoid and fuel pump but Im not sure if the ignition circuit goes thorough it too.
You could remove it if it gives problems you cant resolve, you just need to join the appropriate wires together that are looped.
Does it have 3 pairs of wires?
Edited by Belle427 on Monday 13th April 16:46
Another immobiliser
we all had enough problems with just one unit in there 
That's great news that its got the solenoid circuit running through it. I've been chasing the hot-start, now cold-start issue for literally years without success. Replaced the whole immobiliser/alarm system hoping that it was the well-known relay problem in the META unit but it didn't make any difference. If anything, things got worse. I will be absolutely over the moon if that has been resolved !
Edited by taylormj4 on Tuesday 14th April 16:50
Loubaruch said:
As Belle says it is part of the Immobiliser system.
Ignition amp supply
Fuel pump supply
Starter motor wiring
All pass through these connectors
Awesome, thanks Loubaruch.Ignition amp supply
Fuel pump supply
Starter motor wiring
All pass through these connectors
So despite these wires being all black, they aren't negatives then. That's rather misleading but not surprising
That confirms why the fuel pump was re-priming when I was moving the wiring / connector around with the IGN was ON but engine off.
Temporary interruptions in the starter and fuel pump circuits wouldn't give rough running as you'd expect the engine to ride through a temporary loss in the fuel pump.
You also mention an Ignition Amp. Is that what I would call the Coil or something else (I still have the original ignition system fitted) ?
Interruption of the supply to the coil would certainly cause misfiring
The ignition amp is not the coil, but they are connected to each other.
Depending on your car, the amp will either be attached to the side of the distributor (early cars), or mounted on the bracket that holds the coil - usually with a blue connector visible at the top.
Looks a bit like this:
Depending on your car, the amp will either be attached to the side of the distributor (early cars), or mounted on the bracket that holds the coil - usually with a blue connector visible at the top.
Looks a bit like this:
It is also worth looking at the connectors behind the passenger door post, peel back the carpet to see them that area can get a bit damp so dont be surprised to see dirty connections. The fuel pump is powered through them.
The connections are all black purposely to avoid people tracing the immobiliser circuit.
The connections are all black purposely to avoid people tracing the immobiliser circuit.
PabloGee said:
The ignition amp is not the coil, but they are connected to each other.
Depending on your car, the amp will either be attached to the side of the distributor (early cars), or mounted on the bracket that holds the coil - usually with a blue connector visible at the top.
Looks a bit like this:
Ah, yeah, know what you mean now. That's the electronic version of points I think isn't it.Depending on your car, the amp will either be attached to the side of the distributor (early cars), or mounted on the bracket that holds the coil - usually with a blue connector visible at the top.
Looks a bit like this:
Loubaruch said:
It is also worth looking at the connectors behind the passenger door post, peel back the carpet to see them that area can get a bit damp so dont be surprised to see dirty connections. The fuel pump is powered through them.
The connections are all black purposely to avoid people tracing the immobiliser circuit.
Ah, makes sense on the black wires.The connections are all black purposely to avoid people tracing the immobiliser circuit.
Know the place you mean in the B-post. Had to clean some connectors in there up a long time ago (20years maybe) as the rear lights stopped working.
Probably due another look by now.
Belle427 said:
Looks like you may have resolved it fingers crossed, not a common problem that one so a good find. Be interested to know if you chopped it off and joined the wires or just cleaned it all up?
Cheers Belle,Yes, I've never heard this one on the forums before but I have been away from them for a while.
I should have chopped it off and permanent fixed it but I'm a sucker for keeping things as original as possible so I thought I'd try cleaning it up first and see if that worked. Couldn't see how to clean up the female (loom side) of the connector so just sprayed some contact cleaner in there and worked the joint a few times. I like the yellow sticker with the original dates on it. Also found another larger "Checked by" sheet round the corner, up the loom, behind the carpet, which was fun to find
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