strange loss of power - ignition or injection - please help
Discussion
Hi all,
Following issue is puzzling me - I have a Griff 500 pre-serp 1994, which is so great to drive...
- engine runs perfectly from the start / when cold, meaning smoothly and strongly, with a very stable idling at 800rpm.
- then, above 60-65 degrees (temp shown inboard), at low revs, meaning 1'800-2'000 rpm upwards, strong "engine interruptions" occur - note there are no misfires, bangs whatsoever, just like if erratically a number of cylinders would switch off, or the ignition would fail, or the mixture would not be correct... The car feels like "crazy", shaking unpleasantly, losing and gaining speed for half seconds, even if I did not move my foot...
- If I give more gas, there will be no reaction/same shaky pattern continues, and then all of a sudden, the full ponies are back, car is like jumping ahead... up to high revs.
- idle sometimes goes crazy too, going down to 400rpm during 1-2 seconds, then jumping to 1'500, and so on...
- when the fans cut in, the "shaky" behaviour gets even more erratic, with more violent losses and surges of power...
- at higher revs - say above 3'500, the problem seems not to appear, meaning acceleration from 3'500 to 5'500 is ok (well, like a beast, as the griffith is :-)
- finally it I take off my foot, the engine feels a bit like "dying", like if no ignition would occur at all (a bit like a "on/off" button being pushed)...
What I have checked up to now:
- AFM, lambdas checked, coolant temperatur sensor exchanged
- fault code reader then shows no error (thanks to the author of the bible for providing this very smart tool)
- ignition coil checked (by cooling down with ice pack, again thanks to the same author) - no impact
- in-board voltmeter shows 13V before and after the fans cut in
Thanks in advance for any help,
C14
Following issue is puzzling me - I have a Griff 500 pre-serp 1994, which is so great to drive...
- engine runs perfectly from the start / when cold, meaning smoothly and strongly, with a very stable idling at 800rpm.
- then, above 60-65 degrees (temp shown inboard), at low revs, meaning 1'800-2'000 rpm upwards, strong "engine interruptions" occur - note there are no misfires, bangs whatsoever, just like if erratically a number of cylinders would switch off, or the ignition would fail, or the mixture would not be correct... The car feels like "crazy", shaking unpleasantly, losing and gaining speed for half seconds, even if I did not move my foot...
- If I give more gas, there will be no reaction/same shaky pattern continues, and then all of a sudden, the full ponies are back, car is like jumping ahead... up to high revs.
- idle sometimes goes crazy too, going down to 400rpm during 1-2 seconds, then jumping to 1'500, and so on...
- when the fans cut in, the "shaky" behaviour gets even more erratic, with more violent losses and surges of power...
- at higher revs - say above 3'500, the problem seems not to appear, meaning acceleration from 3'500 to 5'500 is ok (well, like a beast, as the griffith is :-)
- finally it I take off my foot, the engine feels a bit like "dying", like if no ignition would occur at all (a bit like a "on/off" button being pushed)...
What I have checked up to now:
- AFM, lambdas checked, coolant temperatur sensor exchanged
- fault code reader then shows no error (thanks to the author of the bible for providing this very smart tool)
- ignition coil checked (by cooling down with ice pack, again thanks to the same author) - no impact
- in-board voltmeter shows 13V before and after the fans cut in
Thanks in advance for any help,
C14
The problem seem to be heat related, so my initial thoughts are that it is ignition rather than fuel that is the cause of your problem.
I see you'v tried cooling down the coil but I still think that is worth further investigation if you can swap with a known good unit.
The other things that might be worth investigation are the ignition amplifier and the high tension leads.
I see you'v tried cooling down the coil but I still think that is worth further investigation if you can swap with a known good unit.
The other things that might be worth investigation are the ignition amplifier and the high tension leads.
HT Leads, I had I similar sounding problem a couple of years back tried everything but discounted the leads because they were only a few years old, It was the leads.
Eventually the problem was getting worse and would do it most of the time. Found it using a neon telltale device that you hold against a lead to check it’s firing, then finding the offending lead swapping it out temporarily and hey presto. You can get a similar thing from Halfords with LED’s in the plug caps I think.
On the bright side I now have a spare coil, cap, rotor arm and ignition amp for when they do fail.
Cheers,
Simon.
Eventually the problem was getting worse and would do it most of the time. Found it using a neon telltale device that you hold against a lead to check it’s firing, then finding the offending lead swapping it out temporarily and hey presto. You can get a similar thing from Halfords with LED’s in the plug caps I think.
On the bright side I now have a spare coil, cap, rotor arm and ignition amp for when they do fail.
Cheers,
Simon.
Hi,
Thanks for your inputs, Johno you were right, ignition amp exchanged, then issue disappeared. Well almost competely... which means there was more than one problem ?
In fact, over time the initial issue described in my previous post also occured before the trigger point of "fans cutting in" and the car developped "monstruous" shakes/brief complete loss of ignition/and sudden surge of power. This is now sorted by changing the ignition amp.
But! it remains the following: when temperature for switching the fan is reached (about 85deg), the relay for the fans makes a strong rattling noise for say 20-30 seconds. If car is left standing to warm-up, eg at tick-over, then rpm jumps from 900 to 1500 for a couple of sec then drop down again during the relay rattling phase, and if car is put in movement right thereafter then the engine is not as quiet as it should be, just like a notch less power, not "sounding round", then - when the relay stops rattling, the engine feels like boosted, much more aggressive power, "sounding round".
So.... anybody would have a hint on the route cause ? please note that this relay was exchanged 6 months ago following to an electrical fire that started precisely in the area of this relay... so maybe the relay is not the culprit, but the cause would be what made the old relay burn ?
Apologize as this case is a bit a puzzle to me, and at the times the car is ok, it pulls like never before, and I start to believe that I would need a kind of magician for electrics to sort this "riddle"...
Txs,
C14
Thanks for your inputs, Johno you were right, ignition amp exchanged, then issue disappeared. Well almost competely... which means there was more than one problem ?
In fact, over time the initial issue described in my previous post also occured before the trigger point of "fans cutting in" and the car developped "monstruous" shakes/brief complete loss of ignition/and sudden surge of power. This is now sorted by changing the ignition amp.
But! it remains the following: when temperature for switching the fan is reached (about 85deg), the relay for the fans makes a strong rattling noise for say 20-30 seconds. If car is left standing to warm-up, eg at tick-over, then rpm jumps from 900 to 1500 for a couple of sec then drop down again during the relay rattling phase, and if car is put in movement right thereafter then the engine is not as quiet as it should be, just like a notch less power, not "sounding round", then - when the relay stops rattling, the engine feels like boosted, much more aggressive power, "sounding round".
So.... anybody would have a hint on the route cause ? please note that this relay was exchanged 6 months ago following to an electrical fire that started precisely in the area of this relay... so maybe the relay is not the culprit, but the cause would be what made the old relay burn ?
Apologize as this case is a bit a puzzle to me, and at the times the car is ok, it pulls like never before, and I start to believe that I would need a kind of magician for electrics to sort this "riddle"...
Txs,
C14
Maybe your fans or one of them is drawing too much current or even intermittently shorting to earth and thus upsetting the engine control circuit, but this should blow a fuse if wired correctly.
It might be worth disconnecting the fans at the fan plug/socket (near to the fans) and running a simple switch arrangement to battery positive to switch them on when up to temp and see if this solves the problem. This will isolate the fans from the relay and control circuit and take the load away from them. You mentioned that the original relay failed, if you still have it, remove the case and see if the contacts are destroyed or the coil burnt out.
The wiring in the passenger footwell is a nightmare when original but if a previous owner has been fiddling then it could be much worse. Best of luck!
It might be worth disconnecting the fans at the fan plug/socket (near to the fans) and running a simple switch arrangement to battery positive to switch them on when up to temp and see if this solves the problem. This will isolate the fans from the relay and control circuit and take the load away from them. You mentioned that the original relay failed, if you still have it, remove the case and see if the contacts are destroyed or the coil burnt out.
The wiring in the passenger footwell is a nightmare when original but if a previous owner has been fiddling then it could be much worse. Best of luck!
Thanks, will try your suggestions. Unfortunately the original relay is no more available, so cannot check.
What puzzles me is (why is the relay for the fans rattling?): what did cause the fire at that time ? I was driving, then heard a typical noise of electrical shorting, then came quickly some smoke and a plastic smell, then I could stop the fire in a rapid (and lucky) action (with a t-shirt). The upper corner of left side of the fuse box was almost completely burnt, i.e. the box itself, 2 fuses and the relay for the fans. As the fuse box could not be exchanged for an identical TVR part (not available anymore, only as a kind of kit), only the burnt-off part of the fuse was recreated by a bespoke arrangement of 2 fuses and a relay by a specialist car electrician (mandated by the insurance / we unfortunately do not have so many car electrician specialized in TVR here in Switzerland... well I have not found one yet...) and this gentleman could not provide me with an answer why the fire came in the first place, and now I have some strange feeling that the very problem is still unsolved/not localized, and causing the present issue...
What puzzles me is (why is the relay for the fans rattling?): what did cause the fire at that time ? I was driving, then heard a typical noise of electrical shorting, then came quickly some smoke and a plastic smell, then I could stop the fire in a rapid (and lucky) action (with a t-shirt). The upper corner of left side of the fuse box was almost completely burnt, i.e. the box itself, 2 fuses and the relay for the fans. As the fuse box could not be exchanged for an identical TVR part (not available anymore, only as a kind of kit), only the burnt-off part of the fuse was recreated by a bespoke arrangement of 2 fuses and a relay by a specialist car electrician (mandated by the insurance / we unfortunately do not have so many car electrician specialized in TVR here in Switzerland... well I have not found one yet...) and this gentleman could not provide me with an answer why the fire came in the first place, and now I have some strange feeling that the very problem is still unsolved/not localized, and causing the present issue...
Which fuses were destroyed? This may not be relevant but was one (or both) for the fans?
An electrical fire would normally only occur if some component or wiring was being overloaded. The cables that burnt out should give a clue. Perhps some part of the fuse box/relays/loom in the footwell had been shorting to earth?
I seem to remember someone on here knowing the source car for the fusebox, was it a VW?
Hopefully they will respond.
The relays would only rattle if the voltage applied to the coil was rapidly changing. Normally a steady 12 volts across the coil causes the contacts to close. As has been mentioned above perhaps some link with air-conditioning is causing a problem. Does your car have aircon?
An electrical fire would normally only occur if some component or wiring was being overloaded. The cables that burnt out should give a clue. Perhps some part of the fuse box/relays/loom in the footwell had been shorting to earth?
I seem to remember someone on here knowing the source car for the fusebox, was it a VW?
Hopefully they will respond.
The relays would only rattle if the voltage applied to the coil was rapidly changing. Normally a steady 12 volts across the coil causes the contacts to close. As has been mentioned above perhaps some link with air-conditioning is causing a problem. Does your car have aircon?
You could get buzzing relays if something was near short circuit as the relay cuts in. The relay takes 12 volts, but then when it closes and the short occurs the supply to the relay is pulled down far enough to make the relay open again, and the cycle then repeats. Dangerious stuff. This is also likely to spike the ECU supply at the same time.
Edited by blitzracing on Thursday 2nd February 12:26
[quote=blitzracing]You could get buzzing relays if something was near short circuit as the relay cuts in. The relay takes 12 volts, but then when it closes and the short occurs the supply to the relay is pulled down far enough to make the relay open again, and the cycle then repeats. Dangerious stuff. This is also likely to spike the ECU supply at the same time.
Yes, quite so, that is why I suggested isolating the fans as the problem seems to occur when they cut in.
Also if the car was fused correctly this would not occur unless it was a very obscure fault somehow bypassing the fuses.
Yes, quite so, that is why I suggested isolating the fans as the problem seems to occur when they cut in.
Also if the car was fused correctly this would not occur unless it was a very obscure fault somehow bypassing the fuses.
Edited by Loubaruch on Thursday 2nd February 16:45
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