Hesitation and backfire
03-22-2009, 12:21 PM
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Car: 70T/A, 87Formula, 02Hawk, 06 GTO
Engine: 400, 350, LS1, LS2
Transmission: M21, 700r4, T56, 4L65-E
Axle/Gears: 3:55, 2:77, 3:45, 3:46
Hesitation and backfire
Have an 88 Formula 305 TPI and stick. Car has been sitting for a while, month or so. Found a problem with the notorious egr solenoid, with no other vacuum leaks that I can find, but getting some hesitation and backfire thru the TB every once in a while. Checked initial timing, looks like it's around 5 or 6 BTC. Disconnected battery to reset ecu, brought it up to NOT, to kick in the ecu, not throwing any codes. Any ideas? Not sure of the condition of the ignition control module, and have not checked the fuel pressure.
03-23-2009, 12:04 PM
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Car: 70T/A, 87Formula, 02Hawk, 06 GTO
Engine: 400, 350, LS1, LS2
Transmission: M21, 700r4, T56, 4L65-E
Axle/Gears: 3:55, 2:77, 3:45, 3:46
Re: Hesitation and backfire
Alright, swapped out the distro for a known good one. Initial timing is at 6 deg BTC, new cap and rotor. Still wont idle. Engine starts, and can keep it running by gassing it. Still can't find any vacuum leaks. Maybe IAC?
03-23-2009, 06:45 PM
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Car: 70T/A, 87Formula, 02Hawk, 06 GTO
Engine: 400, 350, LS1, LS2
Transmission: M21, 700r4, T56, 4L65-E
Axle/Gears: 3:55, 2:77, 3:45, 3:46
Re: Hesitation and backfire
I pulled the IAC out this morning and cleaned it up. Wasn't even dirty really. If the IAC goes out does it throw a code? Is there a procedure for diagnosing the IAC is working properly?
So I located a leak in the plenum to runner gasket, replaced the plenum to runner gaskets and car is running much better, but not quite as good as it should, still hesitates.
Checked the TPS and it is spot on. .54 up to 4.45 at WOT. No dead spots in the range.
Still have to check the fuel pressure. Anybody know how to check the injectors? I put my ohmeter on them and it was like a closed circuit, the needle went all the way over. On all of them. Think I'll change the fuel filter as well, it might be the original.
Something else that is stumping me, the MAF connector was not even connected when the car showed up my house after a fifty mile road trip! How the heck was it even running?
So I located a leak in the plenum to runner gasket, replaced the plenum to runner gaskets and car is running much better, but not quite as good as it should, still hesitates.
Checked the TPS and it is spot on. .54 up to 4.45 at WOT. No dead spots in the range.
Still have to check the fuel pressure. Anybody know how to check the injectors? I put my ohmeter on them and it was like a closed circuit, the needle went all the way over. On all of them. Think I'll change the fuel filter as well, it might be the original.
Something else that is stumping me, the MAF connector was not even connected when the car showed up my house after a fifty mile road trip! How the heck was it even running?
Last edited by csmith3; 03-23-2009 at 06:51 PM.
03-23-2009, 10:07 PM
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Car: 91 Trans Am
Engine: 355 TPI
Transmission: Built T-5
Re: Hesitation and backfire
ohh it will run with the MAF disconnected....my old 88 gta MAF shorted and bured the ground all the way back into the computer and it still ran lol
03-24-2009, 01:09 PM
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Car: 70T/A, 87Formula, 02Hawk, 06 GTO
Engine: 400, 350, LS1, LS2
Transmission: M21, 700r4, T56, 4L65-E
Axle/Gears: 3:55, 2:77, 3:45, 3:46
Re: Hesitation and backfire
O.K. here's where we are. New O2 sensor, new accel cap and rotor, fixed plenum vacuum leak, fixed dry rotted tubing to the evap canister (vac leak), fixed egr solenoid (vac leak), set timing to 6* BTDC, replaced fuel filter, verified fuel pressure at 38-36 psi., and checked and cleaned the IAC valve. After all the work, have all sensors connected brought the car up to NOT, and hesitates, backfires, and stalls at idle. So disconnected the MAF and the car drives perfect. Suspicion: Bad MAF, but dang they're pricey. Well, just have to drive a while with the MAF disconnected.
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