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Re: Fuel Cut Off Saga (continued) Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 28 Jun 2001 08:40:20
In Reply to: Fuel Cut Off Saga (continued), Bill Cannastra, Wed, 27 Jun 2001 21:05:35 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Definition of terms. When I hear 'hesitation', I think of a minor pause, or slight stumble. In my experience, the fuel cutoff is pretty abrupt - the engine just quits, and since you were accelerating hard right up to that point, you get thrown against the seatbelts.
Hesistation at high boost is usually due to an ignition problem - no spark at high boost. At high boost, it's harder to make a spark jump. Usually the problem is too big a spark plug gap, but it can also be the sign of a tired DI cassette. The non-ignition possiblity is fuel - basically, the fuel system can't keep up with the fuel requirements at high boost, and you start running lean. This could be a weak fuel pump, clogged fuel filter, or bad fuel pressure regulator. A fuel pressure/fuel delivery test can rule that in or out.
Get into about mid-red, and you'll hit the fuel cutoff, which I think you hit from your use of the word 'bang'. The ECU doesn't really limit boost - it's the wastegate actuator. Take the hose off the wastegate actuator, and you'll boost right into the fuel-cutoff. You can lengthen the rod, but if the actuator isn't actuating, it doesn't matter.
I would return the wastegate actuator rod back to where it was. The car didn't come from the factory with this problem (hopefully), so something broke, and I'll bet it wasn't the rod retracting itself by two turns. That only masks the real problem.
I would focus on the wastegate actuator - for some reason, it's not moving. Now, that could be binding at the turbo end (check for movement). It could be a leaky diaphram (apply pressure to the inlet pipe and see that it moves, and that it holds pressure). It could be as simple as a bad hose from the APC solenoid to the wastegate, or that the solenoid is plummed up wrong. A stuck APC solenoid can do it. With the system de-energized, you should be able to blow into the APC hose at the intake manifold (goes to the C line on the APC solenoid), and all that air should go to the wastegate actuator. If it doesn't, find out why - there are very few parts in that path.
If you do go into overboost, the ECU will try and reduce fuel other ways. I haven't followed this thread, so I don't know which model/year you have, (Trionic, LH?, etc). If your car is equipped with a MAP sensor, the ECU will see the high boost pressures and try and reduce fuel flow (hence the big boost swings). The LH can't detect absolute boost pressure, but it can adjust fuel other ways.
Make sure the wastegate actuator and ancilliary plumbing is working properly, and go from there. I wouldn't start replacing parts (actually, you've already replaced most everything already). Troubleshooting is almost always cheaper than new parts.
, Thu, 28 Jun 2001 08:40:20 <-- Viewing This Message, Fri, 29 Jun 2001 12:49:32
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