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Labrat

'91 running rough after warm re-start

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I replaced the MAF and that didn't work.  I then replaced the water temp. sensor under the MAF and no help there either.  The cars feel like it's running rich after starting warm but will run OK after driving a few minutes or revving it up for a minute before driving. 

The coil packs look like new.  The car just turned 80K.  All help would be appreciated.

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You could have an injector leaking fuel into the intake while the engine is turned off. When you start the engine it would run rough until the fuel puddled in the intake is burned off.  A fuel pressure leak down test might help you determine if that is the problem.

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Check the fuel pressure regulator diaphragm. It may be leaking. Pull the vacuum  hose off it and check for fuel . It should be dry on vacuum hose side.

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Still having the problem with idle after the engines is warm. It starts and runs great and is fine until it turn it off and re-start after it has sat for 10 minutes or more.  I  have to rev up the motor to clear the flooded rough feeling before it is drive- able.  Usually about a minute of fast idle clears it up.   It stalled  at a red light twice yesterday.  RPMs dropped below 500 and quit.  Restarted with no problem and ran fine except for fluctuating idle at the next light.  My mechanic over the last few months has replaced the injectors, spark plugs, o2 sensor, water temp sensor,  MAF, TPS (had bad code ) (the only code I've had so far ever) and the IAC.  I don't know if he cleaned under the IAC but will check .  Fuel pressure reg was fine. I don't know if the EGR valve was checked, again I'll ask tomorrow.   The car has 83K miles so it was probably time to change most of the stuff so we did.  I don't mind the cost, I love the car and plan on driving until I'm gone but I've got to get it safe to drive.  Any help would be appreciated.

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My guess..........cam sensor (magnet) other clues are poor gas mileage and poor performance.

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Another Thought

Do you know what the coolant temperature is  while driving it before the problem ?  My thought is that its running in open loop mode  due to coolant leak past thermostat or no Thermostat.  When you stop the car it gets warm enough to do into closed loop where the sensors come into play during the warm restart, Once its has been running again the coolant temperature falls below the sensor threshold and back into open loop.

 

You still have a problem. I would check the Cam Sensor Magnet and I have had more then one bad new OX sensor out of the box, You can unplug the OX sensor and it will stay in open loop.  If running in open loop the problem does away you will need to check all the sensors. The 3 sensors that all affect fuel and air are IAC, MAF and OX.

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I haven't noticed any change in performance, still very peppy and same with gas mileage.  The temp gauge goes to its usual centered position in the right amount of driving.  I thinking in ten minutes of stopping the temp can't fall far enough to matter as the car can have the problem that quick.  I will have the Cam Sensor Magnet checked. and try unplugging the O2 sensor to test it.  Barney how likely is it the cam magnet?  Should I replace the cams sensor at the same time or maybe replace it first to see if that is the problem  Any way to check the sensor before the big tear down?  Also, how is this related to the warm verses cold temp. of the engine?  Thanks.

Edited by Labrat (see edit history)

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This is a TPI engine without EGR and has an integrated PCV system, correct? My first thought was a vacuum leak but less places for that to occur on the L27 engine except the possible exception of where the upper and lower intake manifold bolt together. It seems most of the likely issues have been suggested already, but it would be helpful to have actual sensor readings at warm idle, all of them can be checked, except cam sensor, in diagnostics. 

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I drove it this afternoon and now it is dead.  Will start and run 1 seconds and dies.  I let it cool an hour waiting for the tow truck and no change.  Now maybe my mechanic can find the problem.  He did clean the chamber under the IAC well and replaced the fuel pressure reg during the last attempt to fix it.  He's going to pull the cam sensor and look at the magnet with his camera.  I'm still open to ideas about the problem only occurring when it is up to temp.  Thank goodness for this Forum.

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Needs a fuel pressure gauge on it and a spark test indicator to simultaneously check for fuel and spark when it starts and then stops. Some fuel pressure should remain even if spark goes away.

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Maybe 2seater is on to something altogether different. It could be the fuel pump. I have been told that it is easier to diagnose a "dead" car then one with an intermittent issue.

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It is possible the injectors lose signal too. The engine starts on the ICM under the coils and then control is taken over by the ECM. 

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3 hours ago, Labrat said:

I drove it this afternoon and now it is dead.  Will start and run 1 seconds and dies.  I let it cool an hour waiting for the tow truck and no change.  Now maybe my mechanic can find the problem.  He did clean the chamber under the IAC well and replaced the fuel pressure reg during the last attempt to fix it.  He's going to pull the cam sensor and look at the magnet with his camera.  I'm still open to ideas about the problem only occurring when it is up to temp.  Thank goodness for this Forum.

 

The cam sensor or magnet will not cause the stalling problem you are describing. You can unplug the cam sensor and the engine will still run. 2seater gave you good advice on how to troubleshoot the problem.

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On 2/14/2019 at 4:17 PM, 2seater said:

Needs a fuel pressure gauge on it and a spark test indicator to simultaneously check for fuel and spark when it starts and then stops. Some fuel pressure should remain even if spark goes away.

 

Very good suggestion from 2seater...

 

When I was having similar stalling trouble I got both of those and put them in the back of seat (Not in the stow away) so that I could grab them real quick and do the tests on the side of the road - If need be. I actually did have to do this one day when it stalled - This proved that I did not have an immediate issue with fuel pressure or spark.

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You can leave the spark tester on all the time. I actually thought about buying three of them so I could watch the spark of the front three plugs every time I popped the hood. 

 That way you only have to put the fuel pressure tester on.

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Does anyone have a scanner that you know like a Tech 2?  That can usually pinpoint the problem fairly quickly.

 

Another way to possible get into diagnostics on this car is to do the following.

 

Turn the ignition on and start the car if it will start and press and hold the OFF and WARM buttons on the a/c at the same time and hold the for a few seconds.  If I remember correctly that will put the car into diagnostic mode ( it will on '88's)  and you should be able to see live data from the data stream.  This will include coolant temp that the engine computer sees which might not be the same as the gauges.  You should be able to scroll through all of the inputs to the computers. 

 

Engine temp when warm should be in the 190 F deg range.  Remember that the car will not set a temp code as long as the coolant sensor sends a temp reading between -40 F and I think about 260 F the engine control module.  That can be considered "normal" operating temp.

 

As for the fuel pump, two things to do at the same time.  First hook up a pressure gauge to the fuel rail.  Then get in the car and just turn the ignition on and listen carefully.  It might help to have someone listen under the back of the car.  When you turn the ignition on but not start the car you should hear the fuel pump come on and stay on for about 6-10 seconds.  If no sound, bad pump.  Then look at the fuel gauge. If the pump runs, it should have more than 50PSI. If it has less, then the pump is going bad. A good pump will have about 60 PSI. The car can run sometimes at pressures as low as 40PSI, but not well or intermittently.  Below 40, the car will not run.

 

I could go on, but these are the basics.

 

If you need more information, let me know.

 

 

Edited by Larry Schramm (see edit history)

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I am not certain about the normal fuel pressure for the TPI L27 engine, but the intake and fuel rail pressure I have for a TPI manifold appears to be the same as the '88-'90 LN3, or approximately 3bar or 43.5psi with key on and engine off. I believe later models did use a higher pressure. 

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On 2/16/2019 at 6:36 PM, Larry Schramm said:

Does anyone have a scanner that you know like a Tech 2?  That can usually pinpoint the problem fairly quickly.

 

Another way to possible get into diagnostics on this car is to do the following.

 

Turn the ignition on and start the car if it will start and press and hold the OFF and WARM buttons on the a/c at the same time and hold the for a few seconds.  If I remember correctly that will put the car into diagnostic mode ( it will on '88's)  and you should be able to see live data from the data stream.  This will include coolant temp that the engine computer sees which might not be the same as the gauges.  You should be able to scroll through all of the inputs to the computers. 

 

Engine temp when warm should be in the 190 F deg range.  Remember that the car will not set a temp code as long as the coolant sensor sends a temp reading between -40 F and I think about 260 F the engine control module.  That can be considered "normal" operating temp.

 

As for the fuel pump, two things to do at the same time.  First hook up a pressure gauge to the fuel rail.  Then get in the car and just turn the ignition on and listen carefully.  It might help to have someone listen under the back of the car.  When you turn the ignition on but not start the car you should hear the fuel pump come on and stay on for about 6-10 seconds.  If no sound, bad pump.  Then look at the fuel gauge. If the pump runs, it should have more than 50PSI. If it has less, then the pump is going bad. A good pump will have about 60 PSI. The car can run sometimes at pressures as low as 40PSI, but not well or intermittently.  Below 40, the car will not run.

 

I could go on, but these are the basics.

 

If you need more information, let me know.

 

 

Just throwing out a tech two or any other scanner will not show more than the on board diagnostics. 

One of the awesome things our Reatti do.

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2 minutes ago, D-a-n-i-e-l said:

Just throwing out a tech two or any other scanner will not show more than the on board diagnostics. 

One of the awesome things our Reatti do.

 

I agree, but with a Tech II,  you will be able to see more than two items at a time.  (at least I think that is what I remember)  I have a Tech II and use it all of the time on our cars and friends & family, etc.  There are typically more tests that can be run with a Tech II that can not be done with the onboard diagnostics.

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Mechanic checked the fuel pressure today and it was about 38 psi and bleeds down to 30 in 5 minutes.   What should pressure be.  I saw in and old post where Padgett said anything over 25 was OK.  He replaced the fuel pressure reg. and no change ( i had a spare).  Looks like fuel pump is bad for sure.  Engine started but only ran a minute.  He pulled the plugs and the were black and wet on all 6.  Any way to change the pump without dropping the tank?  Thanks to all for the help so far.

Edited by Labrat (see edit history)

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15 minutes ago, Labrat said:

Mechanic checked the fuel pressure today and it was about 38 psi and bleeds down to 30 in 5 minutes.   What should pressure be.  I saw in and old post where Padgett said anything over 25 was OK.  He replaced the fuel pressure reg. and no change ( i had a spare).  Looks like fuel pump is bad for sure.  Engine started but only ran a minute.  He pulled the plugs and the were black and wet on all 6.  Any way to change the pump without dropping the tank?  Thanks to all for the help so far.

38psi under what conditions? Engine running, engine not running, the details are everything. Bleeding down to 30 that fast is a little excessive, but not horrible. Wet plugs would seem to indicate too much fuel, poor spark or multiple tries to start it with limited results, causing it to go through multiple prime cycles. Hot wire the pump by applying 12volts to the green connector near the brake cylinder to run the pump constantly and see what the results are. Try to start with it hotwired, it won't hurt anything.

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1 hour ago, 2seater said:

38psi under what conditions? Engine running, engine not running, the details are everything. Bleeding down to 30 that fast is a little excessive, but not horrible. Wet plugs would seem to indicate too much fuel, poor spark or multiple tries to start it with limited results, causing it to go through multiple prime cycles. Hot wire the pump by applying 12volts to the green connector near the brake cylinder to run the pump constantly and see what the results are. Try to start with it hotwired, it won't hurt anything.

2seater is right, if you have wet plugs I would think the engine is getting all the fuel it needs. The fuel pump bleeding down to 30 isn't bad either.

 I asked the question before and you said you would have your mechanic look into it. To clean the opening the Idle Air Control fits into. Last fall I bought a '89 Reatta that didn't start or idle good. He had bought but not installed an Idle Air Control  and was sure that was going to fix it. I simply removed the old one sprayed the old IAC with carb cleaner and scrubbed with a tooth brush then did the same with the opening. A lot of gunk flowed out  but after the IAC was back in the car fired right up and ran great.

 These cars have great engines, nothing different then the millions G M used on other cars. Just clean some stuff and then drive them. Who knows maybe your gas is bad because you might not be driving your car enough to keep the gas fresh.

 No reflection on you but I drive my Red and Black thousands of miles a year and have none of the drivability issues I see here on the forum. Even my 'vert gets driven about 100-200 miles a week every week it's out of storage. 

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My mechanic checked the fuel pressure by powering the green connector and the pressure was 42 PSI steady.  After an hour it was 25 PSI.  He is going to re-clean the IAC bowl today.  He checked the coil packs and they had a good blue spark and look to be in great condition.  Running out of things to check.  Aaargh!  I drive the car several times a week so the gas is fresh.  I live in Central Florida so there is no winter storage for me. 

Edited by Labrat (see edit history)

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Fuel pressure sounds good, so likely is not the problem. That leaves two items, spark and fuel injector signal. A noid light or something to indicate off the injector connection would be helpful and spark tester(s) to see if the spark goes out. The two are sort of intertwined so determining which quits first may be difficult. Holding the throttle open slightly will bypass the IAC if that is restricted. I am almost to the point of suggesting the ECM as the culprit but unfamiliar with the '91 electronics. 

Edited by 2seater (see edit history)

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