99 lesabre ignition/wiring problem?

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

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

Have you checked fuel pressure?

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

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

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...

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

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.

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.

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.

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.

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.

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.

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

Many times I've seen corrosion on grounds that are tight. I've had to disconnect the ground, clean, then reconnect. If doing what you did suddenly made the car behave, remove the ignition ground and clean up the contacts. Better yet, go underneath with an ohmmeter and check the resistance between the ground connector and the battery ground, then clean the connection.

i still have same problem. drove 30 miles once and it started but was ok when i got home. yesterday did not make it 1/4 mile and it is messing up now. couple of questions. can i change the ecm without it affecting the security system. key has been bypassed w/resistors but still have the rest of security system intact. i also read that if the oil pressure got low it would cut off the ignition. if i had a bad sensor it should set off a trouble code showing oil pressure problem ,correct?

You can't try just another PCM.........unless it is programmed for your car......

If oil pressure gets low, it will not cut off your fuel......the fuel pump relay is controlled by the PCM, not oil pressure......most older cars have an oil pressure switch, that is a redundant backup to the f/p relay....i.e., if the relay goes bad, as you crank the engine, oil pressure builds, closes a switch, and then powers the f/p......symptom for a failed relay, is a longer than normal extended crank, before the vehicle fires.....

Have you put your hand under the carpetting(can feel dry on top)? If it is wet, there are grounds under there, and could be corroded....

Otherwise, about all you can do is move engine harnesses and harnesses under the dash, to try and create the problem......

Have you pulled the plastic engine cover off the engine and checked for a rodent nest that may have eaten wires? Also, check the wire harness inside the air box to the PCM.....mice like those wires too......

i have taken ground wire straight to battery w/ no improvement. must have been coincidence. drove this morning and it messed up. no traffic so i just coasted. while it was coasting(engine had already died) it would continue to cut off/on. the oil light and the brake light stayed on continously during this. the volt/temp lights/the fuel gage and the radio as well as daylight running lights were off/on. i am now thinking power to radio from battery would be the simplest troubleshooting path of all the things that were cutting off/on to follow. does anyone know where i could find a schematic for this circuit or any for this car that are detailed?

power to radio from battery would be the simplest troubleshooting path of all the things that were cutting off/on to follow. Power to the radio has nothing to do with ignition/fuel delivery.

i realize that. if power to radio is cutting off/on also that may lead me to what is cutting everything else off/on. the problem has to be related somehow

Sounds like it's time to get a scantool. A decent one for home use is a little pricey, but it will probably save you tons of money in the future. You should be able to get a decent one that logs data for about $3-400.

I think a manual full of schematics, would be more valuable.....plus a multimeter and the ability to read and follow schematics....sure sounds like a harness/connection problem....

i have borrowed a scantool w/ drivetime capabilities but unfortunately this car does not support very many drivetime diagnostics. i can read a schematic and have been using multimeter 35 years.i have found a few schematics but i dont think they are detailed enough and i too think its a connection problem. i actually drove car 30 miles today without any problems????

I think a manual full of schematics, would be more valuable.....plus a multimeter and the ability to read and follow schematics....sure sounds like a harness/connection problem....


Right. That would mean the better purchase would be a factory service manual off ebay. I got a complete 2 manual set for $30. It was a little worn, but just as useful.

When were plugs and wires last replaced?

plugs replaced 2 years 18,000 miles ago

With a set of schematics, you can at least look at the wiring diagram of each system that is affected at the same time......Then check power and grounds for each system......finding the common ground or power , could lead you to the area of "concern"....GM likes to use that term....

got a temporary membership to eautorepair.net and downloaded some schematics. must be 25 pages as i wanted to get everything i could within my week. will start trying to narrow down with prints. drove 30 miles today no problem.

Tech 2, does this car have the ground buss under the door sill on the drivers side?

There are grounds all over this car......under the carpet, rear seat, trunk, engine compartment, under the dash, etc.

GM manual not only has a ground schematic , it tells you where every numbered ground is located...

been over a week and 125 miles since it messed up. one of the last things i did that may have helped: i disconnected one of the multipin connectors to computer to see if i could find a place to check for power. put it back on and happy driving ever since. may have been coincidence. wont ever know unless problem returns. thanks to everyone for offering suggestions