Backfire and hestation at low rpm's, searched need addl help
The low down is I have a 91 5.0, FI 302 block, basically in the mornings my car would backfire and hesitate at low rpms then would go away. Now this problem is worse and its prob worse because i just installed a 76mm MAF. My car backfires and hesitates much more but still at low rpms(2,000 or lower). Ive searched but there are so many possiblilities and I want to narrow them down if possible. Plug wires are newer so I ruled that out. Im thinking maybe plugs,fuel pressure, adj timing, or check TPS voltage. Let me know what you think, PLEASE!
Make sure your plugs are good and gapped around .46 or so. Also check to make sure your wires aren't arcing to the headers. Get a gauge and check fuel pressure, you want 39 psi at an idle with the vac. line pulled from the regulator (and capped). Verify .98 volts at the TPS with the throttle closed. Does it run better when warm? How 'bout with the new MAF? Is it calibrated to your injectors?
Scan it for codes.
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1992 Deep Emerald Green Mustang GT Hatch, 5 speed, 2.73s, Mac fenderwell cold air intake, '93 Cobra MAF, Mac 70mm throttle body & spacer, Explorer intakes, Mac unequal headers & offroad pipe, Magnaflow catback, Walbro 110lph fuel pump, Jet adjustable FPR, MSD Blaster coil, Accel 8mm wires, FRPP aluminum quadrant, UPR firewall adjuster, stock cable, Granatelli upper control arms.
Waiting to go on: Granatelli lower control arms, and GT40 Iron heads!
Backfireing would either be too much fuel getting into it, which could be the new throtle body, or it is not enough back pressure which could be a because of the lack of cats, or too big exhaust and not enough power to keep the pressure up. The hessitating could be that it is getting too much fuel also, and it is kind of drowning the engine for a second before it can get it all burned off. It could also be not enough back pressure. If you have no cats, and a large diameter pipe, with a straight flow thru muffler, that is probably your problem. Mine started backfiring when it is cold when I put my catless exhaust on there, and it hesitated a little at low rpms. I had straight flow glass packs on it too. Then I put on some mac mufflers with some back pressure to them, and it completely got rid of the hesitation, and it barely backfires any at all now.
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1983 Mercury Capri - 351w, c4, aluminum heads, huge list of mods 2004 Subaru WRX Impreza - MR catless uppipe, MR 3" catless DP, 2.5" custom DP back exhaust sans muffler and resonator, Cobb AP Stage 2 maps installed.
Yea i will have to check all of the above meangreen, tonight i noticed that just crusing in 4th gear, my car was bucking and low rpms are just terrible. But the car has ran worse with the new MAF but it is calibrated for my 19# injectors. The car was running good for awhile after the MAF install but has just ran like crap lately. Do you think i could have a bad tank of gas? But I will check on some things. Thanks for the replys.
Verify your throttle position sensor. You probably have it way off since you removed the throttle body. Check this post where we talk about it in detail. It's a sticky thread in the main 5.0 tech forum.
I am having a great time with this problem, so i go and purchase a new multimeter voltmeter, i put the sewing needle in the green wire and used the bolt for the ground, turn car key over, and i get NO READING, then i decide to check my voltmeter on the battery, works fine. I had it on a DC settting. Ive tried numerous things to get a reading, does this mean my TPS is bad, or would the car not run at all if there was no reading. Help!
Nevermind guys, after trying about 6 different grounds, i found a good one and got it set to .98 volts(was at .89volts), I ran the car for about 5 mins, so far so good, well see.
Ok adjusting the TPS voltage hasnt helped this problem. Any suggestions? I am going to check my spark plugs and possibly replace those, I am trying to fix this problem the cheapest ways first. I may look into an adj FPR also. Any help is appreciated. Thanks.
Ok an update, I set the TPS to .98volts, wires are away from headers, checked plugs, cap and rotor. I noticed that after the car sits at any length of time even long stop lights, it will backfire, also sometimes the idle will get low then it will run like crap, but after i shut it off and turn back on it will be ok. Is it possible that i could have a leaking injector? Let me know what you think PLEASE!
Yep I am a brand new one. Currently I took off my 76mm MAF cuz this problem has got worse since i put it on. I have checked so many things, fuel pressure is normal, coil is good, plugs, wires, TPS voltage, cap/rotor. My car seems to still run a little weird so far with the stock MAF. We'll see what happens.
Ok now with the stock MAF on this problem is still there and probably worse than before. I am stumped, I guess I might try to find a vaccum leak, look into a fuel filter or fuel pump, or injectors. I dunno, I am def still in for some suggestions please.
Have you tried cleaning your mass air meter wires.It's the very fragile wires inside.The wires will accumulate dust and dirt (more so with a K&N...oil).Need to use a aerosol cleaner that leaves no residue and maybe a q-tip.Be very carful as the wires will break.I know there is info about how to clean them but can't think of hand where.I had a similar problem but at higher rpm. That solved my problem.Might give it a try.
Gerhard
Backfire and hestation at low rpm's, searched need addl help 
