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Help Needed Poor Running engine
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UKdave2002
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PostPosted: Sat May 19, 2007 1:51 pm    Post subject: Help Needed Poor Running engine Reply with quote

Hi

Trying to sort out a problem on my cousins, 1996 Astra which die’s when you open the throttle.
The root of the problem appears to be low induction vacuum, at idle (which is not smooth) the map sensor is 3.8V (very high) which I believe is causing the engine to then run very rich (injector duration is between 3 and 4 ms again high). Compression is good on all cylinders, there are no leaks in the induction system (I blasted compressed air in to the induction system and it held the pressure for a reasonable time).
Swapped the map sensor with a known good one off of his mates car, still get the high readings!
I’ve also checked that there are no other error codes stored (with a simple LED count) .
Am I missing something obvious?

Dave
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1.5ran
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PostPosted: Sat May 19, 2007 7:50 pm    Post subject: Reply with quote

sounds like an air leak inlet manifold or gasket ??
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UKdave2002
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PostPosted: Mon May 21, 2007 9:42 am    Post subject: Reply with quote

Yep, an air leak is what the problem should be!, there was nothing visible so I made a temporary seal over the throttle body and blasted some compressed air in and the pressure holds. The fault is from cold so its not something like a cracked throttle body where the crack opens up with a bit of heat.
I can get the engine to idle better by tricking the engine management system (halved the MAP output voltage with a couple resistors) but it still won’t rev.

Anyone any ideas?

Dave
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UKdave2002
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PostPosted: Tue May 22, 2007 8:30 am    Post subject: Reply with quote

Problem resolved;

I called my local garage; they are not a dealer so this car is quite typical of the age of car they have to work on. They pointed me in the right direction, its quite a common problem, I was on the right tracks with the low induction.

The low induction had been caused by a blocked exhaust, which almost certainly been caused by the catalytic converter collapsing, the resulting debris then chocking up the back box.

I disconnected the back box and the car revved freely again, MAP and injector outputs back to normal.

Great we have identified the fault, but I was hoping for my cousin’s sake it was going to be a faulty MAP or O2 sensor which would have been relatively cheap to replace, now he is going to need a complete exhaust and cat….ouch!

Dave
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