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92 Camero SOMETIMES wont start, backfires or starts rough - but will run fine after it DOES start

HISTORY: 89 Firebird with a 92 Camero engine. V8 - 305 - 2 injector throttle body (tbi). Sat for 9 years in the driveway with a bad fuel pump. RECENT WORK: replaced fuel pump, cleaned fuel tank, removed old gas, replaced both fuel injectors with reman. from Advance. I rebuild the throttle body with a new gasket kit (didn't touch the fuel pressure regulator - but I have a gasket for that if needed), and replaced fuel sending switch on the firewall. Changed oil and oil filter. New drive belt. I have power at the fuel pump - it primes every time. The injectors work - both read the same when I test them with ohms meter, and both spray a mist of fuel (not a dripping spray). It starts fine several time, and starts great AFTER it starts once. But if it sits for a few hours, or a day, it sometimes (intermittently) will start sputtering and not run. She is turning over, and there is fuel being sprayed into the throttle body (fuel system has pressure) , AND there is confirmed spark - but she won't 'catch' and run smoothly. I've gotten it to start twice by removing the air filter and discon/recon the fuel injector wires, but this is after confirming that they were indeed getting signal AND spraying fuel. Weird thing is - after it is done with its temper tantrum, it'll start fine, catch every time, and run fine. I drove her for 20 minutes after her latest tantrum, and not one problem. I start a new job in a week, and need this car to get me there. Any ideas what could be causing this intermittent 'coughing'? Additional Details I forgot - brand new battery too. Engine doesn't run hot, or seem to be skipping. Once running, it does not choke out when I throttle up.

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  • sthetx Feb 10, 2014

    Oh - there IS gray smoke coming from the exhaust - when running fine. It's cold outside and the smoke does disapates, but it's noticable.

  • sthetx Feb 10, 2014

    Thanks all...I have replaced the fuel pump relay. When the car is rough starting, there IS injector pulse, and the injectors are firing what seems to be a normal amount of fuel. Will look into the oil pressure switch.

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  • Cars & Trucks Master
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I would want to know if it is ignition or fuel for sure. There are a few things you can try to narrow down the possible cause.
What does the cap and rotor look like, and is the spark a strong blue when it is running rough ?
Have you checked the actual fuel pressure with a gauge ? Does it matter if you spray carb cleaner or starting fluid into the throttle body ?
Any trouble codes stored in the computer ?
Its possible the coolant temp sensor is wrong and the computer thinks the air temp is 90 degrees instead of say 20 degrees. Or there is moisture in the dist cap or on the plug wires, and so on.

Posted on Feb 10, 2014

Testimonial: "Thank you. I haven't pulled the cap yet. I've confirmed spark because the car 'tries' to start, and eventually will, so Im afraid I can't say that if spark is blue. When starting rough, it won't stay running. But will usually start right up after sitting a few more minutes. No way to test fuel pressure, as there is no schrader valve on the fuel line. No trouble codes (I learned years ago how to get those with a paper clip). I will check out the coolant temp switch. If it was constant, I'd just replace things, but the fact that it WILL start and run fine makes it hard for me to diagnose. Thanks for your time!"

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SOURCE: throttle body injectors not fiering but there is fuel pressure

the injectors are fired thru the engine cotrol module but it gets its signal to fire from the pick-up located inside the distributor if you are loosing injector pulse only the ignition module is bad if you are also loosing spark when you loose injector pulse your pick up is causing the problem if you replace the pick-up i recomend you change the ignition module when doing so because they work together and you have to remove the distributor to change the pick-up

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SOURCE: 90 chevy k1500 350 tbi fuel problem starts but wont stay running

try bypassing the oil pressure switch on the back of the block behind the distributor, if there oil pressure switch goes bad it will do this. had one that drove me nuts trying to fix it then figured out I had to buy a book and low and behold thee it was 3 wire oil pressure switch you can't see between the engine and fire wall just behind the distributor and costs 8 bucks to buy new.

Posted on Jan 16, 2010

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