Random Boost Fall Problem
08-31-2010, 10:50 AM
#1
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Random Boost Fall Problem
6.8 Random Boost Fall Problem.
Statement: I own a 1986 944 Turbo that I bought with 71K miles. Shortly after buying the car I began experiencing problems with the turbo boosting. It will happen randomly and always at a bad time. The problem consists of the turbo only boosting to 1.2 bar rather than the usual 1.8 bar. This becomes extremely annoying while trying to pass on a country road. The problem cures itself when the engine is shut off and immediately started again. I have tried shutting it down and starting several times while coasting into toll booths and I have never had a problem after the restart. About seven months ago I took the car to a Porsche Dealer. The mechanics worked on the car for two hours, which included a few calls to other dealerships. Unfortunately, they could not find the problem. Also has a rough cold idle.
Diagnosis 1: To really nail this down, one would want to do a complete checkout of your exhaust system, consider removing the turbocharger and re-gasket it, and evaluate the waste gate. Putting it on a dyno could help, too, because you could evaluate the exhaust gases at the same time. One reason for the loss of boost can be lack of fuel - leaning - which would be picked up by the sniffer. If fuel were the problem, it could be related to failing fuel pressure regulators on the fuel rail, or a vacuum leak which would compromise the effectiveness of the fuel enrichment system. The frustrating part of this sort of thing is that it is still intermittent, and probably did not show itself to the shop you took it to.
Diagnosis 2: Your problem could be a bad throttle position sensor. The fact that the problem goes away after restart would tend to confirm it. My 87 951 had the same problem early in its life.
Solution: The problem turned out to be the KLR chip.
Statement: I own a 1986 944 Turbo that I bought with 71K miles. Shortly after buying the car I began experiencing problems with the turbo boosting. It will happen randomly and always at a bad time. The problem consists of the turbo only boosting to 1.2 bar rather than the usual 1.8 bar. This becomes extremely annoying while trying to pass on a country road. The problem cures itself when the engine is shut off and immediately started again. I have tried shutting it down and starting several times while coasting into toll booths and I have never had a problem after the restart. About seven months ago I took the car to a Porsche Dealer. The mechanics worked on the car for two hours, which included a few calls to other dealerships. Unfortunately, they could not find the problem. Also has a rough cold idle.
Diagnosis 1: To really nail this down, one would want to do a complete checkout of your exhaust system, consider removing the turbocharger and re-gasket it, and evaluate the waste gate. Putting it on a dyno could help, too, because you could evaluate the exhaust gases at the same time. One reason for the loss of boost can be lack of fuel - leaning - which would be picked up by the sniffer. If fuel were the problem, it could be related to failing fuel pressure regulators on the fuel rail, or a vacuum leak which would compromise the effectiveness of the fuel enrichment system. The frustrating part of this sort of thing is that it is still intermittent, and probably did not show itself to the shop you took it to.
Diagnosis 2: Your problem could be a bad throttle position sensor. The fact that the problem goes away after restart would tend to confirm it. My 87 951 had the same problem early in its life.
Solution: The problem turned out to be the KLR chip.
The DME was replaced with a good used stock unit 3 years ago because the original went haywire after installing an aftermarket chip.
The cycling valve was also replaced with a new unit 3 years ago.
Symptoms are exactly as described in the Clarks Garage testimonial. Tbe car will go into limp mode randomly and the condition is invariably corrected by shutting the engine off and restarting.
What would they imply by the problem being the KLR chip? Do you think only the chip was replaced or the whole KLR unit?
I'm uncertain as to why the KLR would start acting up again after 3 years with the same DME. Would the used DME be failing again now?
TIA
