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1991 Bravada fouls out plugs to point it wont start


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Fomoco
New User

Nov 8, 2012, 10:02 AM

Post #1 of 8 (1444 views)
1991 Bravada fouls out plugs to point it wont start Sign In

Im working on a 91 oldsmobile Bravada with the TBI 4.3L that was brought into my shop for a no start condition it turns out that the plugs were so fouled out that i had to put new ones in it just to get it running, once running i realized that it was running extremely rich it blows black smoke and just being near the engine compartment ur eyes would start to burn, u cant even touch the gas pedal without killing it. so i hooked up the scanner and it showed fault codes for the MAP sensor and The coolant Temp sensor i have replaced those but still get funky reading the coolant temp reading is always -41 degrees never changes even if i unplug it stay the same, and the map sensor is always showing above 4.00v while cranking or running it does fluctuate a bit but not much i believe that is high being that i am just below 3,000ft in elevation. Have tried disconnecting that battery to reset computer but nothing changes still get the same readings. I believe the TPS is tied into the coolant temp sensor somehow was wondering if that could b part of my issue, but my scanner gives me a reading of 0.58v with throttle closed and nearly 5v when wide open so that seems to b working correctly to me. Any ideas would be much appreciated Thank you


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Nov 8, 2012, 10:47 AM

Post #2 of 8 (1416 views)
Re: 1991 Bravada fouls out plugs to point it wont start Sign In

It appears you have either a wiring issue somewhere or a bad ECM, most likely the wiring. It's supposed to read -40 when unplugged but it appears to be still open circuit when plugged in. You are going to have to track down the point of loss.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Fomoco
New User

Nov 8, 2012, 11:27 AM

Post #3 of 8 (1402 views)
Re: 1991 Bravada fouls out plugs to point it wont start Sign In

Im getting the 5v reference signal to the coolant temp sensor and ground, could it b the ground wire is shorting to something before it returns to the computer?


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Nov 8, 2012, 12:49 PM

Post #4 of 8 (1394 views)
Re: 1991 Bravada fouls out plugs to point it wont start Sign In

The CTS and the TPS share the same computer ground so i doubt that. I would more suspect a problem with the plug. You should be able to connect those wires together and get extreme high temp.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Fomoco
New User

Nov 8, 2012, 4:10 PM

Post #5 of 8 (1380 views)
Re: 1991 Bravada fouls out plugs to point it wont start Sign In

Thanks u were right about the plug for the coolant temp sensor got it fixed now it will idle at least, still running very rich though, cant touch the gas pedal without killing it plugs r just coated in black powder after just a few minutes of running. gonna check compression on all cylinders next will post results. Now that it idles i get a code 33 for the MAP sensor or circuit to high and voltage readings 2.89v and 3.00v


Hammer Time
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Hammer Time profile image

Nov 8, 2012, 4:16 PM

Post #6 of 8 (1376 views)
Re: 1991 Bravada fouls out plugs to point it wont start Sign In

You could be looking at any number of things. The throttle body could be leaking fuel. You can check that with a fuel pressure gauge. Make sure the MAP is getting a good vacuum supply. The MAP itself could be bad.

Also, I'm not positive about how the EGR passage is set up but make sure you don't have exhaust leaking at the base of the throttle body into the intake.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Nov 8, 2012, 4:17 PM)


Fomoco
New User

Nov 8, 2012, 4:44 PM

Post #7 of 8 (1369 views)
Re: 1991 Bravada fouls out plugs to point it wont start Sign In

I went ahead and took off the egr and cleaned the ports on the intake and they egr itself and it is closing like it should so that should not be an issue it was stuffed full of soot though. I checked fuel psi.i dont have the specific in line fuel tester for the TBI system so i took the main feed line off at the TBI and hooked my gauge up to it, it only seem to b getting about 5psi, i believe the system is supposed to be between 10-13psi? Dont understand how low fuel psi would cause a rich condition though. put old map sensor back on get same reading trying to find how much vacuum it should have to the map sensor at idle it doesn't seem to have much though. still gonna do compression check


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Nov 8, 2012, 5:07 PM

Post #8 of 8 (1362 views)
Re: 1991 Bravada fouls out plugs to point it wont start Sign In


Quote
is closing like it should so that should not be an issue


Not true. I'm not positive how this one is set up but the old carbed and TBI 350s had an exhaust passage through the base plate, before the EGR that could leak through the base with a closed EGR. Like I said, I don't know if yours is set up that way or not.

The fuel pressure issue could be the leakage I referred to. What happens to the pressure when the key is shut off?

Also try momentarily pinching off the return and see what happens to the pressure.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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