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Ask Derrick Your Own Question
Derrick, ASE Certified Technician
Category: Car
Satisfied Customers: 923
Experience:  A.S.-Automotive Analysis A6-Electrical A8/L1-Engine Performance Cert., CA Chrysler/Jeep/Dodge Tech
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1991 Sunbird: with 120,000 miles..It cranks but wont start...fouled

Customer Question

I have a 1991 Sunbird with 120,000 miles. It cranks but wont start. I first changed the plugs (and wires) because the plugs looked fouled. Still no-start. It looks like its dumping too much fuel into the engine (im watching the injector (TBI) and its pulsing) I checked the compression (135-140 psi on all cylinders), changed the map sensor and changed the coolant temp sensor. The injector doesnt seem to be leaking when its unplugged. If i open the butterfly in the throttle body and look down in, i can see a puddle of fuel after i try to start it.
Submitted: 9 years ago.
Category: Car
Expert:  Derrick replied 9 years ago.

Hi there,

I would start by spraying some brake clean or carb cleaner into the throttle body. Then try and start it. If it starts and runs for a couple of seconds you have a fuel delivery problem. (Check fuel pump, listen to hear if it turns on in the tank when you turn the key on.) If it does not start, you are looking at a timing, compression, spark, or air problem.

You performed a compression test, so we can rule out a compression problem.

I assum cause you are looking down the throttle body that you dont have an air delivery problem, so we can rule that out.

Unless any engine work requiring the removal and installation of engine components has been performed, you probably dont have a timing problem, so we can rule that out.

So, we are left with spark. Check to see if the plug wires are sparking when you turn over the motor. If not i would check the ignition coil, fuses, and wiring.

i hope this helps!

Customer: replied 9 years ago.
Reply to Derrick's Post: I'm getting spark, air and gas. I think i'm getting way too much gas. The car will actually start for a second if i unplug the injector and try to start it (presumably from the fuel still in the manifold), but when i plug the injector in it floods the motor. The injector seems to be working right (because it's pulsing and doesn't leak or anything when it's unplugged) but it's pumping a lot of gas in and the plugs are wet after i try to start it. I also checked the fuel pressure regulator on the throttle body. It doesn't look like there is much to go wrong with it. The diaphragm isn't ruptured or anything.
Expert:  Derrick replied 9 years ago.


Have you checked to make sure the vacuum hose is connected to the fuel pressure regulator? If it is not, the fuel pressure will he high.

Also, have you checked the fuel pressure?

And you said if you unplug one of your injectors it wants to run? If so, it sounds like you would be getting too much fuel.

Customer: replied 9 years ago.
The fuel pressure regulator is integrated into the back of the throttle body, so there isn't a vacuum line. i thought it was getting too much fuel, but i was wrong....

After about 3 days of troubleshooting the fuel system i figured out that the catalytic converter had become plugged. I'm not sure how that happens, but as soon as i loosened the exhaust, it started and ran. It looked like too much fuel because it was all staying in the intake manifold and splashing back out from the backpressure.
Expert:  Derrick replied 9 years ago.

Well that would explain it.

A catalytic converter could become plugged of your engine is not burning the air fuel ratio properly. If you had recently had an O2 Sensor go bad or something like that you could have damaged the cat.

Well I am glad you found your problem!