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Gary, ASE Certified Technician
Category: Pontiac
Satisfied Customers: 916
Experience:  Senior Technician
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Ponyiac Bonneville: I'm getting a random misfire

Customer Question

I'm getting a random misfire
Submitted: 1 year ago.
Category: Pontiac
Expert:  kwiggins29059 replied 1 year ago.
Hello, the next steps would be checking the fuel pressure (should be 53-59PSI) and the vacuum hoses for any cracks or breaks. If you could let me know whether you have the supercharged engine or not I can post the vacuum hose diagrams for you.
Customer: replied 1 year ago.
no supercharger
Expert:  kwiggins29059 replied 1 year ago.
Thanks here's the vacuum diagram.
Customer: replied 1 year ago.
when I turned the key to run fuel pressure went right to 50 psi. after I started it it was 55 it stayed right there with small fluctuations when I'd rev it. When I shut it off pressure is staying at 53. All vacuum hoses look good.
Expert:  kwiggins29059 replied 1 year ago.
Great, there's one last thing to check and that's the EGR valve. You need to remove it and check for carbon build up on the pintle. It's a pretty common issue. You can clean it with carburetor cleaner and they make an aftermarket gasket that has a screen to prevent carbon from getting in there and causing it to stay open. I'll post the removal procedure below.
Customer: replied 1 year ago.
Removed EGR valve. Cleaned it with Carburetor cleaner. Let it completely dry. Reinstalled it with a new gasket and torqued with a torque wrench. Same thing random misfire
Expert:  kwiggins29059 replied 1 year ago.
Thanks, ***** ***** things I can think of is checking that each injector is firing by using a noid light and having the ignition module itself tested at a parts store. I know you mentioned checking coils, did you ohm the plug wire as well?
Customer: replied 1 year ago.
the first thing I did was replace plugs and wires
Expert:  kwiggins29059 replied 1 year ago.
Alright, at this point I've exhausted what I normally check with the exception of scoping the crank sensor. I'm going to open this back up to other experts for you. Someone should be with you shortly.
Customer: replied 1 year ago.
Expert:  Gary replied 1 year ago.
Hi there,I would perform an "upper cylinder clean" with a product like Subaru Upper Engine Cleaner or equivalent.If that doesn't fix it, I would then have the injectors off-car ultrasonically cleaned.Hope this helps.Gary
Customer: replied 1 year ago.
I tried all the auto part stores no one has this or an equivalent. Went to Subaru they don't have Upper Engine Cleaner they have a Fuel injector cleaner part number SOA868V9140. Is that the same thing?
Expert:  Gary replied 1 year ago.
That is odd if you can't find the Subaru product.Here is another one that you should have in the US: local large auto parts store should have this.Gary
Customer: replied 1 year ago.
Used the seafoam per the manufacturers instructions still not fixed
Thanks for your help but I think it's time to take it somewhere
Expert:  Gary replied 1 year ago.
Hi again,Sorry to hear that, but sometimes things do get complicated for the home guys.It could be injectors, it could be valves still not sealing well or worn guides etc.It will need a few more tests, and the injectors are probably next to look at.I hope my advice has been of some help.Please rate my service to you at your earliest convenience.Kind regardsGary