99 lesabre ignition/wiring problem?

[carkivey3]

my car will start everytime, however it will cut off and back on 2-3 times until cutting off completely. i can raise rpms while starting and it will continue to run but it is still cutting off/on. i am not getting a check engine light or a security light. i have already replaced ignition switch. with new sw and the old if i kept the key turned to start position it would run correctly except this will burn up my starter. i feel i am not getting codes because of a bad/faulty connection. the car thinks it is being told to turn off so no problem but when power comes back on the engine is still turning so it fires right back up. my chiltons does not have a great wiring diagram i could follow. if you know where i can get one or if you have seen this problem please let me know. thank you

[DeltaP]

Does the check engine light stay on when you turn the key to 1st position,ignition on?

[carkivey3]

yes it does if you mean without trying to start it. just passed obd2 emissions 10 days ago so light and sensors should be ok

[HotZ28]

Have you checked fuel pressure?

[carkivey3]

45-60 psi.that was the first item i checked. then i thought no fuel should give me check engine lite. anyway fuel pressure good

[carkivey3]

what little is in my chiltons shows pink wire from ignition sw to pcm relay. was able to check at harness under dash. gets hot w/ key in run or start and stays hot even when engine fails

[Tech II]

Remove the vac line to the f/p regulator and check for fuel in the line....

Also try, disconnecting the MAF sensor, and see if the vehicle will start...

[carkivey3]

it does start, everytime, but will cut off/on/off/on/off. i had already tried disconnecting maf.

[enslow]

Originally Posted by carkivey3

my car will start everytime, however it will cut off and back on 2-3 times until cutting off completely. i can raise rpms while starting and it will continue to run but it is still cutting off/on. i am not getting a check engine light or a security light. i have already replaced ignition switch. with new sw and the old if i kept the key turned to start position it would run correctly except this will burn up my starter. i feel i am not getting codes because of a bad/faulty connection. the car thinks it is being told to turn off so no problem but when power comes back on the engine is still turning so it fires right back up. my chiltons does not have a great wiring diagram i could follow. if you know where i can get one or if you have seen this problem please let me know. thank you

Does it run normally as long as you keep your foot on the accelerator? This is soundling a little like the IAC valve.

[carkivey3]

when i raise rpms it still cuts off/on but with higher rpms it stays running because the rpms dont drop low enough when power is off momentarily to completely die before it gets power again. did u see the part about holding key in start position it does not cut off.

[enslow]

If you can get your hands on a scantool that records live data, this will be very useful to you. Hook up the scantool to record, start the car and hold the accelerator so the scantool can record the attempts to "cut out". When you download the information, you should be able to see what sensor is cutting out.



Also, with the scantool, monitor the misses to see if the miss is on one cylinder or on multiple cylinders.

If it's missing on multiple cylinders, the cause could be anything from plugs/wires to engine controls. Because the engine continues to run without actually stalling (although it does try to cut out), I believe your fuel pressure is good.

If the miss is on one cylinder, I'd suspect plugs, wires, or a faulty injector.



I am assuming you have checked the usual maintenance things like plugs and wires. I have heard of new plugs and wires failing badly.

[enslow]

Originally Posted by carkivey3

when i raise rpms it still cuts off/on but with higher rpms it stays running because the rpms dont drop low enough when power is off momentarily to completely die before it gets power again. did u see the part about holding key in start position it does not cut off.

Unless I'm mistaken, all this will do is use the starter to keep the engine running through the cut-outs so you won't notice the stumbles. I'm not convinced holding the key in the start position has any diagnostic value.

[carkivey3]

holding key is not for diagnostics. just for some reason it is keeps power where otherwise in run position it loses it. the starter cannot turn fast enough to keep engine running @ 800-100 rpms. i do not have access to a run time scantool but please realize i am not having firing problems. the ignition appears to be turning off and back on. if i were having firing problems the o2 sensors would pick that up and set off codes.

[enslow]

Originally Posted by carkivey3

holding key is not for diagnostics. just for some reason it is keeps power where otherwise in run position it loses it. the starter cannot turn fast enough to keep engine running @ 800-100 rpms. i do not have access to a run time scantool but please realize i am not having firing problems. the ignition appears to be turning off and back on. if i were having firing problems the o2 sensors would pick that up and set off codes.

Not necessarily. If firing problems are not consequetive for more than a few cycle, it will not set a code, but will be detected with a scantool in a live data mode. Engine misses detected by a scantool can be due to many reasons that are not firing problems.

I would be very tempted to get a run-time scantool if you can afford one. You should be able to get a decent on for about $300-400, and may very well pay for itself by solving this one problem. The run-time scantool can monitor all engine parameters including voltage and rpm. You should detect the engine trying to cut out by seeing the rpm change, then look at the other data and see if there was another parameter that caused the rpm to change. I caught a bad MAF sensor this way, although it sounds like your MAF sensor is good.

As soon as we're talking about the pcm and problems with engine controls it's really hit and miss (excuse the pun) without a scantool.

[carkivey3]

worse case scenario happened. problem disappeared. i was checking grounds and was told ignition circuit ground is next to oil pressure sensor. i checked it and it was not loose and appeared fine. nixt time i tried to start it, everything was fine. i went back under while it was running and wiggled the dround but nothing happened. i cant go far in this car cause i dont trust it till problem found