Car dies under 35kmp - Chevy Impala SS Forum
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post #1 of 11 (permalink) Old 04-20-2014, 11:24 PM Thread Starter
m/w
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Car dies under 35kmp

hello from the great white north where all the snow was gone and then we got another 10 inches. we just put on a set of long tube headers on my sons 91 caprice with an lo3 engine . Before the conversion the car never stalled and ran just fine . Hank and tim(son &nephew ) removed the air pump system that ran into stock exhaust .They welded an o2 bung at the collector and ran a new wire .The car starts great hot or cold and drives ok cold but as soon as its up to temp it likes to die at stop lights etc .If you give the gas a quick shot of gas before the stop sign it usually wont stall .Hank rebuilt the tbi and changed most sensors , each time he did one of these things it stalled at a lower speed till it would only do it at or under 35 kmp. Has anyone experienced anything liken to this and if so what's the fix .As always thanks for the input . Later Bake
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post #2 of 11 (permalink) Old 04-21-2014, 08:25 AM
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Did it do this from the very first with the headers? Did you reposition the sender for the oil pressure so you do not overheat the unit? I used a plumbing elbow and a 1 1/2 inch nipple to face the sender toward the back. You may need a heat shield for the oil pressure sender. If the car does not see a minimum of 4 psi, it may shut off. You could also check the ground at the thermostat. It is the ground for the computer and the O2 sensor. Are you throwing a code?

I have shorty headers, and sometimes mine will have a swinging idle that would end up with the engine stalling. The computer goes into closed loop when it is warmed up. I think mine is an O2 sensor issue, because I installed a new one, and it pretty much went away. Occasionally it will reappear in a subdued manner, and I have had it quit occasionally. You could try installing a heated O2 sensor. The sensor is much farther from the head, and it may have a lag time that the computer can not keep up with, or it may set up an out of phase signal input for the injectors to keep the mixture correct, because of heating and cooling of the O2 sensor. This is just a guess, because I have been having some weird issues with mine.

You might also try raising your fuel pressure a little. If you put a washer about the thickness of a quarter under the spring in the fuel pressure regulator it could help.

1991 OCC 461 (.030 over 454) BBC, 3.23 posi, flash to pass, drop spindles & springs, Impala rims, Hydroboost, Recaros, MOMO/wood SW w/QR, custom wood shift knob, Pioneer DEH P77DH
1992 OCC now with 5.7 tbi, DEH P77DH
For a parts list, check https://www.impalassforum.com/vBulle...ion-parts.html
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post #3 of 11 (permalink) Old 04-22-2014, 09:46 AM Thread Starter
m/w
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Thanks for the info. No the car is not throwing codes to the best of my knowledge .I will check with the kid when he gets home.Yes once again to the best of my knowledge this was a thing right from the beginning and no he did not reposition the oil sender ,will check all this out. Just a thought the boys ran a wire from the collector to the factory wiring harness and soldered in a new piece of wire ,now what gauge of wire would be the best to use . If there is a poor solder joint that could also make the computer act wonky . Thanks again later Bake.
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post #4 of 11 (permalink) Old 04-22-2014, 12:48 PM
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The wire on my O2 sensor was stainless steel, and would not solder. I used an inline crimp to make a patch cable, so I could swap out the O2 if it ever goes bad. I also used a cable clip attached to the top screw on the flywheel cover to keep it away from the header. The O2 bung should be high on the collector to keep it from getting wet from condensation. The wire for the oil pressure sender will reach even with it relocated. The wire I used was from a junk yard harness, so I do not know what gauge it is. I would suspect 16 gauge if I were to guess. If there was a disconnect between the O2 sensor, and the computer you would get a CEL. Do the changes one at a time, so that you know which one fixed the problem.

Going to a heated O2 sensor would make sure that the O2 sensor is not cooling off too much and giving a poor reading.

When you do not get a CEL, it is usually a fuel issue, but a marginal sensor issue could cause an issue without throwing a code.

1991 OCC 461 (.030 over 454) BBC, 3.23 posi, flash to pass, drop spindles & springs, Impala rims, Hydroboost, Recaros, MOMO/wood SW w/QR, custom wood shift knob, Pioneer DEH P77DH
1992 OCC now with 5.7 tbi, DEH P77DH
For a parts list, check https://www.impalassforum.com/vBulle...ion-parts.html
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post #5 of 11 (permalink) Old 04-22-2014, 09:13 PM Thread Starter
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I really hate to sound stupid but what's a cel ? Later Bake
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post #6 of 11 (permalink) Old 04-22-2014, 09:16 PM
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Check Engine Light

1991 OCC 461 (.030 over 454) BBC, 3.23 posi, flash to pass, drop spindles & springs, Impala rims, Hydroboost, Recaros, MOMO/wood SW w/QR, custom wood shift knob, Pioneer DEH P77DH
1992 OCC now with 5.7 tbi, DEH P77DH
For a parts list, check https://www.impalassforum.com/vBulle...ion-parts.html
Fred Kiehl is online now  
post #7 of 11 (permalink) Old 04-26-2014, 12:11 AM Thread Starter
m/w
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Sorry to sound like a dummy thanks for the great info fellas will attack the car asap . This has nothing to do with the cumputer getting a bit weak does it ?
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post #8 of 11 (permalink) Old 04-26-2014, 06:08 AM
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The computer can not get "weak". It works, or it does not.

1991 OCC 461 (.030 over 454) BBC, 3.23 posi, flash to pass, drop spindles & springs, Impala rims, Hydroboost, Recaros, MOMO/wood SW w/QR, custom wood shift knob, Pioneer DEH P77DH
1992 OCC now with 5.7 tbi, DEH P77DH
For a parts list, check https://www.impalassforum.com/vBulle...ion-parts.html
Fred Kiehl is online now  
post #9 of 11 (permalink) Old 05-12-2014, 12:56 AM Thread Starter
m/w
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Sorry for the late reply ,i was away working any way we've had older vehicles (early 90s GMs) that ran just abit funny and put in a different computer and it seemed to help . This is what i meant ,sorry if i was unclear .
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post #10 of 11 (permalink) Old 05-12-2014, 07:24 AM
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Changing the computer will not make a difference. The difference between computers is the chip. The headers may give the computer enough erroneous information that it thinks the mixture is too rich, and lean it out. stabbing the gas pedal could allow the computer to get the mixture info to keep the mixture a little richer at idle. You could redo the wire from the O2 sensor to see if it makes a difference. The fact that it is not throwing a code, implies that all of the sensors are doing their job, and the issue is with a non-monitored system. Fuel would be my first direction. As to what it is doing, you can not monitor the fuel pressure unless you install a fuel line from a 91, 92, or 93 Fleetwood (91 and 92 with an LO3/5) that has a Schrader valve port. Other than the fuel check, using a heated O2 sensor (because you changed its location) is the only other item that I would suspect causing the stalling. The long tube headers set up a resonant frequency pressure wave in the pipe to extract gasses from the cylinder head. If that frequency causes the O2 sensor to have an exhaust pulse hit it at a time when it is showing a rich mixture, the computer may lean the mixture at the injector. It may not be enough to trip the CEL, but enough to lean the mixture to the point where it stalls. This is all speculation, but I can not check the specifics. You might consider having a garage put it on a computer to verify the information sent by the sensors.

1991 OCC 461 (.030 over 454) BBC, 3.23 posi, flash to pass, drop spindles & springs, Impala rims, Hydroboost, Recaros, MOMO/wood SW w/QR, custom wood shift knob, Pioneer DEH P77DH
1992 OCC now with 5.7 tbi, DEH P77DH
For a parts list, check https://www.impalassforum.com/vBulle...ion-parts.html
Fred Kiehl is online now  
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