944 Engine Problem
Discussion
Been suffering with a badly running engine the last 3 weeks. The mechanical managed to sort out the low end idling by replacing the plugs which did the trick. But there is still problem at the high end. At 80-100mph I put my foot down and the car starts jolting forward and loosing power. There is plenty of boost so its not the turbo. Also, this occurance is AFTER they replaced the air flow sensor (£275.00 part!) If anything the jolting (which was more a case of dropping out before) is now more pronounced. Is this a case of the Airflow being incorrecly installed or tuned or could it be another problem alltogether? I am still not sure if the air flow sensor was functioning incorrectly in the first place. Could it be another type of fuel problem? Really scratching here and as I have spent $hit loads getting this far I really want to get this sorted fast. Many thanks
When I started reading this, I instantly thought it sounded like a dodgy air flow meter. Then you said that you've had a new one, and it only got worse. I'd suspect that you've had a duff one fitted.
Was it a new part, or did it come from another car? It would be worth getting it checked over, as this seems to be the most likely cause of your problem.
Was it a new part, or did it come from another car? It would be worth getting it checked over, as this seems to be the most likely cause of your problem.
I had the same thing occasionally on my 944 Turbo. It was quite dangerous because I had to cane the arse off it to try and replicate the fault (normally under load in high gear). After doing a scary 130mph test drive on a B-road and behaving immaculately I left it alone... it was just too dangerous to try and isolate or replicate... then I went to overtake something one day and it missed/jolted quite badly. Never got to the bottom of it. Very annoying. Hope you fix it; the airflow sensor connection sounds like a likely candidate. Fuel pump relay could also be worth replacing.
Well I got the car back finally. It turned out to be holes in the airbox trunking and idle control hose. They also replaced the turbo bypass valve and left the new airflow meter in as the old one was giving the wrong reading when they subbed it in to try and identify the new problem. Cheers
Oh No! Its back with a vengance. Still dropping out in third under full power. Does anyone have any idea what the problem is. Once more the Turbo boost is fine, the fuel sensor has already been replaced so I now am sure this was not the problem in the first place. Hoses intact. Your help would be greatly apreciated. Regards
verychilled said:
Oh No! Its back with a vengance. Still dropping out in third under full power.
This now sounds very much like the overboost protection stepping in. The standard ECU will only allow a maximum of .85 bar of boost (1.85 absolute on your gauge). If you go over this for more than a few seconds, it will step in and cut the fuel, which feels like you've hit a brick wall. The car will run rough for a few minutes or you can reset it by switching off and on.
Turbos of our age suffer from many boost and vacumm leaks through old and brittle piping. Now that you have had some of yours replaced it looks like you are back to full power (and a little more).
If you have a manual boost controller valve leading down to the wastegate, then try turning it down a click at a time until you stop getting overboost. You will get overboost more often as the weather gets cooler and the turbo gets more efficient
. When I had standard chips, I used to turn mine down in the winter and up again in the summer. Modified chips will allow a higher boost level
but leads down the slippery slope of more and more power. You know you want to
The car is still at the mechanic. They have finally isolated the problem. As you suspected it is over boosting and the engine shuts down to prevent damage. The thing is they are not sure exactly what the problem is. I am guessing either engine management electrics or maybe something mechanical? It has taken them this long to get this far so any further suggestions would be welcome.....
verychilled said:
any further suggestions would be welcome.....
Just a thought, had similar on a chipped 220 & the thinking was that there are I belive 2 chips on a 944T that need changing when chipping & only one had been done & thus it occasionally then triggered overboost & it missed like a bugger on boost if this had been triggered.
Turning the ignition on & off was a tempory cure for this tho & it was ok untill the next time it was triggered.
Thanks for you advice and pictures. Spoke with the mechanic yesterday. My 944 is an unmodified turbo. They have apparantly isolated the problem as a wategate or interelated issue, not electrics. The car runs fine with both the wastegate and the electrics isolated. The faulty timed valve has also been ruled out. All the pipes have now been replaced as was the fuel sensor. An earlier poster talked about this happening at 120mph+. It happens to mine under full boost at 90mph so must absolutely be fixed. I want the confidence that this will not happen when overtaking a articulated lorry on a two way road with limited space....
Well the mechanic finally called today. After replacing the airflow sensor, timed valve, knock sensor etc etc etc all to no avail he finally announced it was the injection unit. Has anyone ever hear of this problem? Am I right in saying this should have been checked first? I welcome all comments.....
verychilled said:
Well the mechanic finally called today. After replacing the airflow sensor, timed valve, knock sensor etc etc etc all to no avail he finally announced it was the injection unit. Has anyone ever hear of this problem? Am I right in saying this should have been checked first? I welcome all comments.....
as with any multisystem operation, everything needs to work for it to work. its irritating to have had all that work done perhaps unnecessarily but its very easy to be wise after the event and say a) or b) should have been checked in a different order. I would take it on the chin - your car is fixed and if it does go wrong again you will know that "the airflow sensor, timed valve, knock sensor etc etc" are probably not to blame!
Not even sure what he/you means by an injection unit. I would have checked the pipe from the cycling valve to the wastegate. If you have a good wastegate and this hose is leaking (goes brittle at connection to wastegate due to heat) you may get the overboost protection to trip in cold weather - as with boost control device in that line. A non standard banj bolt could also cause this. Bad earths can often cause wierdness with the 944t engine. Who is the mechanic?
Tony
Tony
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