Car down on power – diagnostics help needed
Discussion
For the last 9 months I’ve been reading about other people’s engine problems and hoping it would never be my turn. Now it is...
1998 Griff 500. It started after a trip up and over the Grossglocker in Austria, the highest part of the road is 2500m, I’m not sure if this is relevant or not but I thought I’d include it regardless. 30 min after the decent we had a driver change, I jumped in and no power. In 1st gear it has some power up to about 3200 rpm, but in higher gears it runs out of power much lower, say 2200 rpm. It will rev past this and it will do it smoothly, just no power.
I checked the one of the lambdas, it operated correctly at idle but under load dropped to 0 suggesting too much oxygen. I thought I’d go for the easy and obvious fix as it felt like a fuel problem. I changed the fuel filter and it made no difference. Whilst at the rear of the car I convinced myself the fuel pump was making funny cavitating noises so I changed this with a new Bosch unit, still no improvement.
Next I tried to test the fuel regulator. I used my bike pump with a built in pressure gauge to connect to the fuel rail to test at what pressure the regulator opened up and returned to the fuel tank. The bike pump could not pressurise the fuel rail past 28psi, I could hear/feel the fuel regulator letting the air past. I got a new Lucas fuel regulator which was marked as the correct 2.5 BAR (36 psi) and fitted this. The bike test pump test showed the same value and the problem was not fixed. I guess the regulator behaves differently with air and fuel or the new one was DOA???
Somewhere through the testing I also had error code 23 on the fault code reader – low fuel pressure. There is no pressure sensor on our cars and I understand this is just the ECU guessing at the fault....
Next, I measured out the throttle pot. I couldn’t find the 5kohms between pins 3 & 25 but I could find the correct and smooth voltage change across pin 20 and earth as I depressed the gas pedal so I assume this is ok??? I ran the car up to temp and the temp sensor connected to the ECU measured correctly all the way. I measured the AFM and it seems a little high, 1.9v on idle, 2.3v at 1500rpm. Today I drove (slowly) to another a friend’s who also owns a Griff 500, we swapped both the coil and AFM, no change.
What else? I don’t think its the fuel quality, it happened when I was half way through a tank and I’ve put fuel in twice since. There are no sparks or lights when I watch the engine running at night. All the HT leads look ok as does the rotor arm, dist cap.
Any ideas on how to test further? I’m living in Vienna so I have no idea on TVR friendly garages over here.
Regards Anthony
1998 Griff 500. It started after a trip up and over the Grossglocker in Austria, the highest part of the road is 2500m, I’m not sure if this is relevant or not but I thought I’d include it regardless. 30 min after the decent we had a driver change, I jumped in and no power. In 1st gear it has some power up to about 3200 rpm, but in higher gears it runs out of power much lower, say 2200 rpm. It will rev past this and it will do it smoothly, just no power.
I checked the one of the lambdas, it operated correctly at idle but under load dropped to 0 suggesting too much oxygen. I thought I’d go for the easy and obvious fix as it felt like a fuel problem. I changed the fuel filter and it made no difference. Whilst at the rear of the car I convinced myself the fuel pump was making funny cavitating noises so I changed this with a new Bosch unit, still no improvement.
Next I tried to test the fuel regulator. I used my bike pump with a built in pressure gauge to connect to the fuel rail to test at what pressure the regulator opened up and returned to the fuel tank. The bike pump could not pressurise the fuel rail past 28psi, I could hear/feel the fuel regulator letting the air past. I got a new Lucas fuel regulator which was marked as the correct 2.5 BAR (36 psi) and fitted this. The bike test pump test showed the same value and the problem was not fixed. I guess the regulator behaves differently with air and fuel or the new one was DOA???
Somewhere through the testing I also had error code 23 on the fault code reader – low fuel pressure. There is no pressure sensor on our cars and I understand this is just the ECU guessing at the fault....
Next, I measured out the throttle pot. I couldn’t find the 5kohms between pins 3 & 25 but I could find the correct and smooth voltage change across pin 20 and earth as I depressed the gas pedal so I assume this is ok??? I ran the car up to temp and the temp sensor connected to the ECU measured correctly all the way. I measured the AFM and it seems a little high, 1.9v on idle, 2.3v at 1500rpm. Today I drove (slowly) to another a friend’s who also owns a Griff 500, we swapped both the coil and AFM, no change.
What else? I don’t think its the fuel quality, it happened when I was half way through a tank and I’ve put fuel in twice since. There are no sparks or lights when I watch the engine running at night. All the HT leads look ok as does the rotor arm, dist cap.
Any ideas on how to test further? I’m living in Vienna so I have no idea on TVR friendly garages over here.
Regards Anthony
Sorry to hear of you woes.
Looks as if you have checked most things... Lambdas I think kick in around 3000rpm and I am led to believe* they are hard to test and aren't cheap to change if aren't faulty.
I have a spare ignition module if you like i would happily send it over for you to try?
Dirty/faulty injectors may cause the problem to have you looked at the plugs and seen whats happening in each bank? Maybe worth taking injectors out and getting them cleaned or try some cleaner in your fuel and see if this does anything.
I am sure some more knowledgeable peeps will be along in a mo to add to the above
BB
Looks as if you have checked most things... Lambdas I think kick in around 3000rpm and I am led to believe* they are hard to test and aren't cheap to change if aren't faulty.
I have a spare ignition module if you like i would happily send it over for you to try?
Dirty/faulty injectors may cause the problem to have you looked at the plugs and seen whats happening in each bank? Maybe worth taking injectors out and getting them cleaned or try some cleaner in your fuel and see if this does anything.
I am sure some more knowledgeable peeps will be along in a mo to add to the above
BB
- heard this somewhere but cant be 100%
dnb said:
Lambdas work up to 3000rpm. After that, they are ignored.
I'm wondering if it's partially blocked precats? You seem to have covered all the electrical things.
I'm wondering if it's partially blocked precats? You seem to have covered all the electrical things.
Edited by dnb on Saturday 13th September 21:56
Cheers Dave i think i have been corrected on that before 
Have you got Steve Heaths book theres a good section on it on page 92 talking about readings and possible probs with readings... Carbon cans/injectors etc
BB
thanks Matt,
I use this pump to pump my mountainbike tyres up to 40-60 psi so its enough, but yes the gauge may be wrong or the regulator "regulates" air differently to fuel.
Have ordered a proper fuel pressure gauge, hopefully it will arrive in a few days so I can test at the fuel rail and at the fuel pump...
cheers
Anthony
I use this pump to pump my mountainbike tyres up to 40-60 psi so its enough, but yes the gauge may be wrong or the regulator "regulates" air differently to fuel.
Have ordered a proper fuel pressure gauge, hopefully it will arrive in a few days so I can test at the fuel rail and at the fuel pump...
cheers
Anthony
coetzeeh said:
I wonder if the altitude change had anything to do with it.
Whatever controls the fuel/air ratio may have become confused during the ascend to 8000ft and subsequent descend.
(from a tech numpty)
Very nice idea, but the 14cux is not that that smart (or stupid...) It just resets the air fuel ratio (long term fuel trim)at tickover after about 10 -20 seconds of idle time, each time the car ticks over, so you dont even need an ecu reset. This is the only point when all the sensor input are stable so the ecu only has mixture to "worry" about. To create this situation would have to be it was allowed to tickover at 8000 ft, but not since.......Whatever controls the fuel/air ratio may have become confused during the ascend to 8000ft and subsequent descend.
(from a tech numpty)
Mark
Hi Anthony,
Probably a long shot; have you checked the fuel pump and injector relays (located in the footwell wiring loom)? I think you told me that you had done some work on the fuse board, so maybe something got disturbed or maybe the driver swap started the problem due to long legs pushing on the passenger footwell stuff
If you haven't a spare relay try swapping them over. I think they are identical.
Probably a long shot; have you checked the fuel pump and injector relays (located in the footwell wiring loom)? I think you told me that you had done some work on the fuse board, so maybe something got disturbed or maybe the driver swap started the problem due to long legs pushing on the passenger footwell stuff
If you haven't a spare relay try swapping them over. I think they are identical.
Edited by m4rk on Monday 15th September 09:04
Interesting idea, there is a 12 volt supply on the injectors on one side, and the other side is earthed by the ecu when it opens an injector. So you can measure the 12 volt rail, and it should be constant at 12 volts. If a the fuel relay contacts had gone to a higher resistance, you will see the voltage drop significantly when the engine runs. Mind you the relays would get pretty hot as well.
Mark
Mark
And now some closure...
You can read what else I did and tested or you can just scroll down to the picture and laugh...
I got my hands on a fuel pressure gauge and found I had a solid 2.6 BAR or pressure with the vacuum pipe removed. Went for a drive with the gauge in place, all ok.
Popped the plugs out, all a bit sooty and a wet one in each bank. Cleaned them and dried them as best I could. Fault code 23 (low fuel pressure) really means both lambdas are similar and the ECU is enriching as much as possible. I assumed the high altitude together with some small HT problems may cause the plug fouling, poor spark and low lambda readings. I ordered new leads, rotor arm and distributor cap, all pretty cheap and easy to get and fitted them yesterday along with a Ignition Amp from BB, no help. Today I realised I didn’t reset the ECU after the previous day’s changes so I did this and went for another drive and had a rather complete failure. The car would hardly idle, wouldn’t rev past 1500 rpm and a terrible howling noise started under the bonnet. I thought I’d really screwed it and melted the cats or something causing the exhaust gaskets to blow but the noise was coming from the plenum. Then I noticed it looked like the plenum was trying to suck the AFM off the side of the engine bay, a quick look down the air intake pipe showed that it has completely collapsed on itself! I guess it was slowly getting worse, the more it collapsed the more it was sucking itself off the wire coil.
Disconnected the pipe from the AFM, car instantly felt better, more revvy and happily dropped two large rubber lines down my street (I just couldn’t help it after three and half weeks of sleepless frustration)
Now all I have to do is pick up the pieces of my life that I’ve been ignoring since the cars been sick....
You can read what else I did and tested or you can just scroll down to the picture and laugh...
I got my hands on a fuel pressure gauge and found I had a solid 2.6 BAR or pressure with the vacuum pipe removed. Went for a drive with the gauge in place, all ok.
Popped the plugs out, all a bit sooty and a wet one in each bank. Cleaned them and dried them as best I could. Fault code 23 (low fuel pressure) really means both lambdas are similar and the ECU is enriching as much as possible. I assumed the high altitude together with some small HT problems may cause the plug fouling, poor spark and low lambda readings. I ordered new leads, rotor arm and distributor cap, all pretty cheap and easy to get and fitted them yesterday along with a Ignition Amp from BB, no help. Today I realised I didn’t reset the ECU after the previous day’s changes so I did this and went for another drive and had a rather complete failure. The car would hardly idle, wouldn’t rev past 1500 rpm and a terrible howling noise started under the bonnet. I thought I’d really screwed it and melted the cats or something causing the exhaust gaskets to blow but the noise was coming from the plenum. Then I noticed it looked like the plenum was trying to suck the AFM off the side of the engine bay, a quick look down the air intake pipe showed that it has completely collapsed on itself! I guess it was slowly getting worse, the more it collapsed the more it was sucking itself off the wire coil.
Disconnected the pipe from the AFM, car instantly felt better, more revvy and happily dropped two large rubber lines down my street (I just couldn’t help it after three and half weeks of sleepless frustration)
Now all I have to do is pick up the pieces of my life that I’ve been ignoring since the cars been sick....
Hi Mark,
Yes, I'll order one tomorrow am.
It had started collapsing a little a while ago, I noticed when I changed a cooling fan but I left it as a "winter job" you can see the rusty bits which had already left the wire but it looked like it was holind up ok. I guess it got very bad very quick. I don't know if I had a different fuel or HT fault to start with or not, probably not, but today the hose gave way 100%.
Anyone got any pics of the ACT pipe meeting the air box in a Griff? Its tight enough in there with the old felxible hose, how do you get the heavy ACT one to join the air box and still get the air box to sit flat on the panel filter?
Cheers
Yes, I'll order one tomorrow am.
It had started collapsing a little a while ago, I noticed when I changed a cooling fan but I left it as a "winter job" you can see the rusty bits which had already left the wire but it looked like it was holind up ok. I guess it got very bad very quick. I don't know if I had a different fuel or HT fault to start with or not, probably not, but today the hose gave way 100%.
Anyone got any pics of the ACT pipe meeting the air box in a Griff? Its tight enough in there with the old felxible hose, how do you get the heavy ACT one to join the air box and still get the air box to sit flat on the panel filter?
Cheers
Interesting foot note to the diagnosis. The ECU was perfectly correct flagging up a low fuel pressure error, as with the intake pipe blocked, there is a massive vacuume in the plenum chamber even with the throttle wide open. This has the effect of causing the fuel pressure regulator to drop the fuel pressure, when it should be at maximum pressure, so both banks run lean, and generate a low fuel pressure error as both the lambda probes detect the lean mixture. Odd thing is the AFM output would be also be very low for the given throttle pot position, but this situtation occurs when you floor the throttle at low revs, before the air flow really picks up as the revs rise, so it would not be an error condition without the wrong Lambda readings.
Live and learn......
Mark
Live and learn......
Mark
Edited by blitzracing on Thursday 25th September 18:09
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