Engine Misfire After H/c/i Swap

Landon116 · Feb 26, 2015

Hey guys, after searching the forum for a thread that could help me, I had to make a new thread. I recently installed fresh ported GT40P heads with spring kit, B-303 Cam and Gt40 intake. The car is a 1992 5.0 Lx 5 speed. I got the car fired up after doing a base idle reset, it idles perfect. My problem is that whenever a load is applied to the car while driving, there is a heavy misfire. I mean, if your familiar with doing a cylinder balance test and when the PCM turns off an injector, it sounds like that. Best way I can describe it. It has a farily new distributor (TFI included) and most sensors. plug wires a motorcraft wires with Autolite 764's.

Not asking anyone to solve my problems I just really need some direction. I advanced base timing from 10 degrees to 15 degrees and definitely saw some improvement but far from perfect. Still heavily misfires.

I will be installing a wideband this weekend to see what my AFR is. any help is appreciated. Thanks guys!

mikestang63 · Feb 26, 2015

run the codes- it could be many things

timing
bad TFI or distributor
vacuum leak
fuel pressure
misadjusted valvetrain
mismatched MAF, EEC, injectors

I wouldnt be driving the car until you get the cleared up.

Landon116 · Feb 26, 2015

running the codes was the very first thing I did. only codes I got were emissions because they were removed by PO. what do you think are the limits of the 19lb injectors are without running them at 100% duty cycle ?

mikestang63 · Feb 26, 2015

you are fine with 19's and your combo. What TFI and distributor? Don't tell me it's MSD

Landon116 · Feb 26, 2015

Nope just the stock ignition , I know how trouble some msd can be. It's a stock replacement Auto zone duralast gold. everything was good until the swap. I might try swapping distributors out.

mikestang63 · Feb 26, 2015

is your distributor phased properly. Did you install it with #1 at TDC and line up the rotor to the #1 on the cap

Landon116 · Feb 26, 2015

Yes when I reinstalled it I put #1 at tdc on the compression stroke and lined up the rotor for #1 then set base timing with engine running with spout out. I will most likely go back through the procedure again just to double check. The misfire is only present when you get about half throttle into it while driving. it's fine when cruising. I am afraid to drive it right now it's so bad. Also I'm going to check that my injectors are plugged in all the way. I let my girlfriend plug them in because I forgot to plug them in before I put the intake on. my hands were too big to do it lol.

A5literMan · Feb 26, 2015

Have you checked for vacuum leak? Slipped intake basket? Did you degree the cam? Didn't accidentally retard/advance it? Could be a bad injector or not installed properly. Also check the tfi. Even if it's fairly new. I'd grab another one to test with. It only acts up under load? No idle issues?

Landon116 · Feb 26, 2015

it only acts up under load. When the engine was first cranked it had idle surging but after a base idle reset it idles great. I will get home and check everything. Thanks for all the suggestions so far guys.

Landon116 · Feb 26, 2015

Also the cam was installed dot to dot. and I burnt a plug wire but recently found a spare one to replace it

mikestang63 · Feb 26, 2015

I would start by swapping in a factory ford OEM distributor and TFI. I have never had any luck with aftermarket ones. If you need to get a new one, rock auto sells them under the Cardone brand- they are Ford in the box.

I think this is the one

Product Detail

Call them to confirm

7991LXnSHO · Feb 26, 2015

Since it runs fine until part throttle and has emission codes only, I would check the TPS for a smooth transition of readings across the whole range of motion. If it has a bad contact mid range, the wrong signal will confuse the computer. I am not talking about the mythical .999 Volts.
Help @jrichker I can not find a link to this, but here is what I would do.

Using the same wires as checking the TPS base idle voltage with the key on but not running, keep the leads hooked up. Slowly move the throttle the whole range and keep your eye on the display to make sure there are no jump up or down on reading.

Hardinkyle5.0 · Feb 26, 2015

Sounds like your not getting fuel man when's the last time you checked your pickup on your fuel pump?

mikestang63 · Feb 26, 2015

I'd think if his TPS was bad he'd see the codes 23 53 or 63 , have a rough idle and hesitation when he hits the gas.

Landon116 · Feb 26, 2015

Alright guys, I swapped in a new distributor and TFI with cap and rotor and got NO change. Set base timing to 10 degrees. At idle I see it jump around from 10 to 20 with he spout in depending on idle speed. Timing advances as throttle is increased. I will check out my TPS out again and my fuel pump is new ( about 500 miles on it). I also did some wire tucking on the passenger side and unhooked a few things like the Salt and pepper shakers, so ill check them out. Leaning towards a fuel problem right now.
Thanks for all the suggestions guys

Hardinkyle5.0 · Feb 26, 2015

Put a fuel pressure gauge on it and run it see how much you got

7991LXnSHO · Feb 26, 2015

mikestang63 said:
I'd think if his TPS was bad he'd see the codes 23 53 or 63 , have a rough idle and hesitation when he hits the gas.

I have seen a bad TPS do fine at idle and full throttle fine, but send bad news signals at part throttle like a radio volume potentiometer that makes static when you change the volume. It felt like a blown power valve and accelerator pump combined. I figure when it is under load, the pedal gets pushed at least a bit.

Funny, as I was thinking If it was the pip or tif, it would have idle or hot running condition issues.

Fuel is my next guess if we are both wrong, and that has been suggested.

Another cheap question or two for the OP. You mentioned the cyl balance test. Does it pass that test? The ignition has to work harder under load than at idle, so a borderline part could cause the described problem if fuel checks out. I would be tempted to mist all the wires and cap, then run the test again, even looking for sparking wires, then carbon tracks or a crack in the cap or rotor.

Landon116 · Feb 26, 2015

7991LXnSHO said:
I have seen a bad TPS do fine at idle and full throttle fine, but send bad news signals at part throttle like a radio volume potentiometer that makes static when you change the volume. I figure when it is under load, the pedal gets pushed.
Funny, as I was thinking If it was the pip or tif, it would have idle or hot running conditions.

Fuel is my next guess if we are both wrong, and that has been suggested.

Going to go test it right now

Landon116 · Feb 26, 2015

TPS tested fine , smooth transition from 0.97v to 4.7 volts. Gotta be fuel or a connection..

7991LXnSHO · Feb 26, 2015

That it idled and does not code is a good sign to me that it is something not too complicated or expensive (besides the fuel pump, that is a hassle with a full tank.) Be encouraged and check the fuel and ignition farther.

Engine Misfire After H/c/i Swap

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At least it is lumpy...

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wanna catch the space herp

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wanna catch the space herp

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wanna catch the space herp

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Engine Misfire After H/c/i Swap

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