94 Buick baffling

Discussion in 'Shop Talk' started by agmantoo, Dec 31, 2004.

  1. agmantoo

    agmantoo agmantoo Supporter

    Messages:
    10,854
    Joined:
    May 22, 2003
    Location:
    Zone 7
    I have been working on this car with no luck. Any thoughts?
    1994 Buick 3.8 166K miles, new tps, new fuel filter, fuel pressures tests OK (37psi and jumps to 47 when the vacuum is removed from fuel regulator), engine idles fine and will readily start. No code info as this is the transistion year and it is neither OBD I or OBD II. When the accelerator is depressed and at estimated 14 to 16 hundred RPM the engine struggles briefly and dies. Engine will restart immediately and symptons will repeat. Car can be driven if the accelerator is gently depressed, when running the engine is smooth and quiet.
     
  2. Beeman

    Beeman Well-Known Member

    Messages:
    6,977
    Joined:
    Dec 28, 2002
    Location:
    East TN
    Very little to go on except to try a guess. There is a mass air flow sensor mounted in the throttle body. It is the black rectangle with wires plugged into it. Remove the sensor and it will have a round tube part that goes into the throttle body. At the end of that tube there are wires that sense the amount of air flowing into the throttle body. If those wires become dirty they will not be able to sense air flow. Use choke or brake cleaner and spray the wires. Be very gentle, and look at them with a magnifying glass. If the are dirty they will usually only have dirt on one side, the side the air flows from.
     

  3. agmantoo

    agmantoo agmantoo Supporter

    Messages:
    10,854
    Joined:
    May 22, 2003
    Location:
    Zone 7
    Thanks Beeman, I will do as you suggest and report on the results.
     
  4. Timber

    Timber Well-Known Member

    Messages:
    87
    Joined:
    Jun 15, 2003
    Location:
    NE Ohio
    "if the accelerator is gently depressed, when running the engine is smooth and quiet." Are you getting over the cutoff RPM point?

    A restriction in exhaust system? Maybe plugged catalysis converter, or the old potato in tail pipe trick?

    Timber
     
  5. Beeman

    Beeman Well-Known Member

    Messages:
    6,977
    Joined:
    Dec 28, 2002
    Location:
    East TN
    If the wires of the MAF sensor are dirty be sure to check the seal of the air filter box and the integrity of the hoses going to the throttle body. Unfiltered air will contaminate the sensor quickly.
     
  6. agmantoo

    agmantoo agmantoo Supporter

    Messages:
    10,854
    Joined:
    May 22, 2003
    Location:
    Zone 7
    Timber, the cutoff of the engine appears to occur always at the same RPM. Almost like a rev limiter but I am way below that. There is no blockage to the exhaust system as I can best determine.

    Beeman,
    No luck with the MAF. It was not dirty. However, I did clean everything as discussed and to no benefit. I have determined that the engine has the fault at cold start as well as after reaching operating temp. The car has an Inlet Air Temp (IAT) Is there anything to check there?
     
  7. Beeman

    Beeman Well-Known Member

    Messages:
    6,977
    Joined:
    Dec 28, 2002
    Location:
    East TN
    Yes there's a air temp sensor and a coolant temp sensor. they both operate so that the hotter they get the lower the resistance. I don't have a manual near me right now but you can measure the resistance of the sensor and compare it to what it should read at the temp it is. Disconnecting a sensor will have it show high resistance or cold temp to the engine so it will run richer. When you disconnect the sensor you will turn on the ck. engine lite and set a code. If you do get someone with a scan tool to read the codes you will have plenty of false codes that you have set that will need to be cleared out before diagnosis can begin.
    94 is a changeover year so you probably actually have OBD1 with an OBD2 connector. The emmissions sticker under the hood will say what systen you have.
     
  8. Timber

    Timber Well-Known Member

    Messages:
    87
    Joined:
    Jun 15, 2003
    Location:
    NE Ohio
    "Almost like a rev limiter" sounds like a frequency problem.
    Maybe I'm off base on this call, but doesn't it sounds like a crank sensor problem. Or maybe a camshaft sensor, or dirty cam interrupter?

    If you can't retrieve a code, with simple tools maybe put a dwell meter on the coil see if the dwell falls off. Check the supply voltage to the coil, see if when the engine reaches the rev cutoff point the voltage is shut off. Not knowing GM, this car has a Ignition Module/Control Unit and computer? Maybe the computer senses something and kills the IMCU.

    Timber

    Or back to simple fixes maybe a mouse has build a nest in the intake, air filter, but then you said it dies sharply.

    Good luck
     
  9. twohawlks

    twohawlks Member

    Messages:
    17
    Joined:
    Oct 14, 2003
    From your discription of the problem it sounds like it might be fuel related, I would start buy checking the injectors, you can measure the resistance of each injector , they should all have about the same resistance.
     
  10. daeve

    daeve Well-Known Member

    Messages:
    61
    Joined:
    Jan 24, 2003
    Location:
    East Central Alabama
    When you are measuring the fuel pressure, are the readings you gave at idle or at the point the engine dies?

    If at idle, monitor the pressure as the engine dies. I have seen GM's (and others) where the fuel pump would produce enough fuel volume to run at idle but not at speed or under load. At 166k if the pump hasn't been replaced it is REAL close to it's end of life.

    Another thing to check is the vacuum. You state that the fuel pressure on the rail goes up when the vacuum line is disconnected. Have you checked the vacuum with a gauge both when idling and as it dies?

    If the exhaust is plugged (stopped up catalytic converter, collapsed inner wall of double wall exhaust pipe, neither of which can be detected via visual observation) then the vacuum will drop (as opposed to going up as it should) as the rpm increases and if it gets below a certain point the computer should kill the engine.

    Just my $0.02
     
  11. agmantoo

    agmantoo agmantoo Supporter

    Messages:
    10,854
    Joined:
    May 22, 2003
    Location:
    Zone 7
    The fuel pressure was observed at idle and at time of failure. The rise in fuel pressure was observed at idle as I removed the vacuum line. It behaves as the Haynes manual said it would. I have used a vacuum gauge and the vacuum remains good and there are no vacuum leaks in the various hoses. I installed a small vacuum pump that is 110 volt driven into the system's vacuum lines and observed that there were no leaks. When the engine faulters, it will die but will restart immediately. During the time it faulters I do notice a slight drop in fuel pressure (a few pounds) but I attribute that to the alternator dropping voltage. Fuel pressure remains on the rail after the engine has died and that pressure is as high or higher than idle pressure was.
    I have determined that the OBD connector is an OBD II and that the wiring to the connector is something orther than OBD II. The decal at the engine states this is a phase-in model. I saw on the internet an adapter sold to make the 94/95 3.8 engines readable with a specific OBD II scanner but could not find the details of the adapter to where I could make one. I guess my attitude on fixing this is rather hardheaded and I should compromise and take the car to a dealer that has the equipment. Does anyone know other than the fuel pump what components in the fuel system could cause this failure? I am aware that many of the emission sensors impact the fuel as to rich or lean but I am hazzy as to which components would cause the fuel to cease to be delivered or uncombustionable. This vehicle has 3 coils and I have not been able to adequately determine for certain that the fuel delivery is the problem. The behavior of the engine when it dies leads me to think it is fuel starvation since there is no backfiring, popping. engine miss. Later today I may try to determine if the injectors cease to get a signal when the engine dies. I have attempted to verified that all the wires/cable connectors are in place and that there are no broken ones. The only way that I can get the engine to die is by revving the engine to the specific speed that equates to about 45 MPH. The failure will repeat itself consistently and all the symptoms remain the same.
     
  12. Timber

    Timber Well-Known Member

    Messages:
    87
    Joined:
    Jun 15, 2003
    Location:
    NE Ohio
    agmantoo , Try some of the big chain auto stores for a scan. Some are willing to do this service for free business. Autozone around here.

    Try a Actron 9145. http://www.actron.com/product_detail.php?pid=16150
    Amazon had it for 25 bucks off and free shipping last fall. I think total was around $175.
    It has live data viewing (i.e.O2 voltages)and updateable. This winter I've must have used it twenty times or better. It's a great tool.
    Timber
     
  13. agmantoo

    agmantoo agmantoo Supporter

    Messages:
    10,854
    Joined:
    May 22, 2003
    Location:
    Zone 7
    After extensive research and scratching both ends I have concluded the problem is the crank position sensor. I have read that the crank sensor will not give a code and therefore it is useless for me to proceed with an attempt to get the PCM read. Replacing the crank sensor entails removing the vibration damper from what I have read. Does anyone know for fact that the only way to replace the sensor requires removing the damper?
     
  14. Beeman

    Beeman Well-Known Member

    Messages:
    6,977
    Joined:
    Dec 28, 2002
    Location:
    East TN
    Yes removing the balancer is required and requires special bolts to remove balancer. Not a bolt you can buy at the parts store but actually part of the special tool, old puller will work if you can get the bolts. Look at tool company web site to see bolts, either Snapon or Mac show them. Crank sensor will also have to be gauged into position, dealer has a nifty tool for this, can be done with 2 feeler gauges preferably non magnetic plastic.
    It doesn't sound like a crank sensor failure but I'm not saying it couldn't be. A quick test for a crank sensor was to tap it lightly with the engine running. I use my 3ft socket extension and just tap lightly. If the engine dies when tapping it means a bad sensor. Now I say tapping and mean it, you don't have to hammer on it.
     
  15. Beeman

    Beeman Well-Known Member

    Messages:
    6,977
    Joined:
    Dec 28, 2002
    Location:
    East TN
    I just reread your original post and it says you replaced the TPS. Was there a specific reason for this or was it replaced in the elimination process for this problem?
    A very common problem on these cars is a coolant leak at either the throttle body or the plenum. I have seen coolant run into the TPS and also into the connector and the harness. Possibly you have corrosion in the connector or the harness?
     
  16. herefordman

    herefordman Well-Known Member

    Messages:
    194
    Joined:
    Aug 24, 2004
    Location:
    washington/british columbia
    Take a close look at the damper, I had a 3.8 litre, and the outside diameter of the damper became delaminated from the inside diameter and was slipping back and forth causing crank trigger faults and engine stalling all the time.
    I picked up a new one from a wrecker and all fixed !!
     
  17. agmantoo

    agmantoo agmantoo Supporter

    Messages:
    10,854
    Joined:
    May 22, 2003
    Location:
    Zone 7
    I changed the TPS because when I checked it with my Ohm meter it had a small place where their seemed to be a dead spot in the resistance reading. You could say I changed it out of desperation or that I was gropping also :).
    Recently, I injured my hand and it is getting well and within another week to 10 days I will resume the attempt to repair the car.
    I will examine the damper very closely to see if it has deteriated or interferring in any way with the crank sensor. I have located the specialty tool for setting the clearance and will purchase it for the task. I have a choice of several brands of crank sensor, Echlein, Wells, Sorensen, ACDelco.....any preference?
     
  18. herefordman

    herefordman Well-Known Member

    Messages:
    194
    Joined:
    Aug 24, 2004
    Location:
    washington/british columbia
    I would stick with the AC Delco
     
  19. mightybooboo

    mightybooboo Well-Known Member

    Messages:
    11,301
    Joined:
    Feb 10, 2004
    Location:
    So Cal Mtns
    Autozone will also LOAN the specialty tools to pull hubs and such,just pay a small deposit.They loaned me a scanner at the store,I couldnt get the darned thing plugged in right,a guy there came out and plugged it in for me.

    The problem was this,I got the code,but their readout for that code was way off.It was for coolant sensor and their code book said some crazy thing like 'bank 2 voltage drop'

    What the heck was that???

    So I went to a VW site online,posted code,and got the right answer,along with pictures on what to pull to get to it.
    Fixed problem for less than 10 bucks,all thanks to Autozones help and a web sites help.

    Point being,you dont have to buy a scanner or those specialty tools,free sources are out there.

    BooBoo
     
  20. agmantoo

    agmantoo agmantoo Supporter

    Messages:
    10,854
    Joined:
    May 22, 2003
    Location:
    Zone 7
    Beeman, unfortunately for me you were correct it that it is not the crank position sensor. I also know the problem is not the throttle position sensor and it is not the electronic pack under the 3 coils. I have checked for all wires being secure, the battery connections are clean and the voltage is good to everything, no hoses are loose or spraying coolant anywhere. The exhaust does not appear to be hindered. The engine idles better than one would expect for a high mileage engine: it is quiet, no excess valve noise, no internal rattling. I caught some fuel out the fuel rail shrader valve using a small hose and valve and the volume seems fine and I know the pressure is good as mentioned above. I attempted to feed some fuel into the intake as the engine die trying to ascertain whether the proble is electrical or fuel. That had no impact other than to flood the engine. I had expected to get the engine to rev at bit as I did this while trying to give the engine some throttle. In summary, nothing has changed....the engine starts and idles but will die with any attempt to accelerate beyond a fast idle. Any thoughts?