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AMEDEE
AMEDEE, CHEVY TECHNICIAN
Category: Chevy
Satisfied Customers: 24415
Experience:  ASE certified tech ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
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Chevrolet 91 gmc 3500: 91 gmc 3500 5.7 tbi starts and idles

Customer Question

91 gmc 3500 5.7 tbi starts and idles good for about 20 seconds and the dies tbi still making fuel spray right up until motor stops....will start right back up and do the same thing after about 12 -15 starts it finally stays running and then runs great...thought fuel and added another external pump to bypass relay still doing it and as i said it has a good fuel pattern right up until the motor completely stops
Submitted: 7 months ago.
Category: Chevy
Expert:  AMEDEE replied 7 months ago.
Hello and welcome! My name is ***** ***** I can assist you with your question. Are you saying that the engine cranks but does not start? However, it runs on starting fluid?
Customer: replied 7 months ago.
NO... it starts right up and idles perfectly for 20 - 30 second and thrn dies.. i thought at first it was a fuel delivery issue so i installed another fule pump outside the tank still starts right up and idles for 20 -30 seconds and dies.. there is a good spray from the tbi injectors right up until the engine stops running and it will not restart if you do not turn the key to the off position first after you do this 10 or 15 times the truck then deceides to stay running
Expert:  AMEDEE replied 7 months ago.
So when it stalls, the engine has spark but the injectors stop spraying fuel? Is that correct?
Customer: replied 7 months ago.
no..the injectors continue to spray and there is spark until the motor qiuts turning...it sounds like when it starts to idle down after running 20 seconds or so that it just chokes out
Expert:  AMEDEE replied 7 months ago.
Can you keep the engine running if you step on the gas pedal just a bit when it is about to stall out??
Customer: replied 7 months ago.
no all you hear is a sucking noise from the tbi(vacuum) seems when is starts to idle is when it chokes out as long as it idles fast seems ok
Customer: replied 7 months ago.
sorry let me make this more clear ...truck starts fine and goes to fast idle for 20 -30 seconds and then when idle drops down to normal after a few seconds it starts to sound like its choking out( a sucking sound through the tbi and then sputters a couple times and then dies) but will restart imediately and do the same thing again...what are the symptoms of a bad iac motor( and is there a way to test the iac motor
Expert:  AMEDEE replied 7 months ago.
Thank you for the extra information. YES, it could be a bad IAC motor. The best way to check the circuit is to use an IAC tester. This plugs into the connector and it should blink as the computer tries to control the idle (move the pintle in or out). Here is a link to a noid light set that has this tool you can use to check the IAC signal from the computer. http://www.amazon.com/Tools-5612-11-Piece-Noid-Light/dp/B000OUX9R2
Customer: replied 7 months ago.
i dont have iac tester but let me ask you ...should the pintle on the iac motor move in or out when you turn the key on?? i just took mine out plugged it in ..turned key to run position and pintle never moved
Expert:  AMEDEE replied 7 months ago.
It may or may not depending on where the computer wants the engine idle to be based on certain inputs.. intake air temp, TPS voltage, and MAP sensor signal..
Customer: replied 7 months ago.
is there a way to check the plug for voltage with a multimeter??
Expert:  AMEDEE replied 7 months ago.
You can try but it may not be very accurate..
Customer: replied 7 months ago.
just to see if there is a signal from the ecm...i just dont get why after 15 or so tries it starts and idle and drive perfectly
Expert:  AMEDEE replied 7 months ago.
I understand. I would start by checking the IAC signal from the PCM using that tool in the link above and go from there.
Customer: replied 7 months ago.
i dont think it is the iac motor( but i will get a noid test kit tomorrow) i read online that 2 wires on the iac plug will show hot which they did with key on i did notice when the motor started to choke the check engine lite would come on and then motor would die shortly there after...any other ideas????
Expert:  AMEDEE replied 7 months ago.
YES, a bad ignition switch, bad computer, air/vacuum leak map sensor or even a bad engine or frame ground.
Customer: replied 7 months ago.
amedee...checked the map sensor..good..checked all the grounds..good......hard to think computor or ignition switch because it kicks on the check engine lite on right before it stalls and the fires right back up and the cel goes out let me ask you this...i always though that this truck had an issue with fuel delievery i installed a holley pump on the frame(14 psi) but left the pump and pickup in the tank if the oem pump or relay stops the pump will it still let fuel pass through it that is being pulled up by the new external pump...what i cant figure is that there is still a good fuel spray right until the motor stops rotating ..this last time that cel came on and motor stalled .. i shorted the a-b terminals on the diag plug without turning the key off and got code 34(map signal low or high voltage ) and code 54 (fuel pump curcuit) but then it would fire right back up
Expert:  AMEDEE replied 7 months ago.
Hello! Maybe it would be best if we talked over the phone. It will be so much easier to hammer out the details speaking with each other.
Customer: replied 7 months ago.
for another 26.00 ????
Expert:  AMEDEE replied 7 months ago.
Phone calls are extra. It does not have to be an additional $26. How about $12? Is that fair?
Customer: replied 7 months ago.
amedee...i dont think so...i dont really feel like we are getting any where here.....i have used this service a few times before and seem to get into the probl;em a little better than we are here...so we are going to have to start making some progress or i need to look else where for help...
Expert:  AMEDEE replied 7 months ago.
I understand. I recommended a phone call because we are not making any progress. It would be much easier to do this over the phone rather than typing back and forth.
Expert:  AMEDEE replied 7 months ago.
And to be honest with you, I am not sure I understand you completely..
Expert:  AMEDEE replied 7 months ago.
Thats why it would be much easier over the phone..
Customer: replied 7 months ago.
maybe tomorrow .....i am going to bed
Expert:  AMEDEE replied 7 months ago.
ok, no problem. Have a good night!
Customer: replied 7 months ago.
amadee...will you please opt out so maybe i can find another expert..thank you
Expert:  AMEDEE replied 7 months ago.
will do!
Customer: replied 7 months ago.
thank you

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