Just finished rebuilding the 302 in my 87 F150, AOD, 4x4
installed FMS x303 heads and comp cam 31-255-5, and FMS roller rockers
"junkyard" MAF conversion was done last fall, a9p stang computer
fired it up last week and ran 1500-2200 rpm for 30 minutes for cam breakin.

New plugs(AGSF32C-gapped 0.044"), FMS wires, dist cap and rotor were installed for the rebuild. Base timing was set to 12*BTDC, I double checked to make sure the timing pointer was on true top dead center and reset base timing. Wires are routed so adjacent cylinders are not crossing.

starts and idles fine, no problems.

problem: sometimes on acceleration it seems to miss fire, whole truck shakes, shudders, engine makes loud popping noises. If I get the pedal down enough it kicks in and runs fine. Seems to have issues between 1000 and 2000 rpm.

so far I have checked fuel pressure at idle, 37 PSI. put on parking brake, put transmission in gear hold brake pedal and gas pedal, stays at 37 PSI. I tried putting an extension hose on the fuel pressure gauge so I could watch while driving but that didn't work as expected...
manifold vacuum reads about 15-18 at idle, needle is steady.
I pulled the vacuum hose from egr valve and plugged the hose, runs better but I still get the misfiring. I also replaced the TPS, douched the MAF with tuner wash, swapped the MAF with a spare, checked all vac hoses and sensor connectors.
I borrowed a friends sunpro A/F ratio gauge, shows running ideal-rich on acceleration, all over the place the rest of the time.

Last night when it did it I noticed the temp gauge was reading low, like the thermostsat was stuck open. I'll check into that and see what I can find out.

At this point I'm thinking I might pull the stang computer and put the Speed density computer back in but I don't know how it will handle the new cam and heads.

I'm really running out of ideas and starting to grasp straws here.

Anyone have any suggestions or experience with something like this?

TIA
Brian

 

your speed density ecu wont run that motor period. go to fordfuelinjection.com to pull codes and test that ecu. maybe its bad? Also when you set the timing was that with the spout disconnected? you might try backing it off to say 10*btdc with spout removed. is your fuel filter new? what type of plugs are you using as in brand and type.

 

oh i also forgot to ask, how many o2 sensors are you running? mass air requires 2. each one should be reading from either side of exhaust manifold near the collectors. if your still running one that could be an issue as well.

 

I forgot to mention that I had pulled codes and only codes 85 and 95 show up, one is for cannister purge solenoid error, which there is no sol. the other is for fuel pump feedback which basically needs a wire connected back to the ECU from the pump armature. Those codes have been present since the conversion last fall.

The spout was pulled out when I set the base timing. I can back it down to 10* btdc. Fuel filter was replaced in april.

Plugs are motorcraft AGSF-32C, per FMS website for the heads. I gapped at 0.044" since that is the original spec for the truck and "assumed" the ignition system wanted a gap of 0.044"

I considered the single o2 sensor as a problem. The signal from the single sensor is fed into both inputs on the ECU. It worked fine before the rebuild. Would the cam and heads change the system enough to make a difference?

Thanks
Brian

 

they could have made a difference. i think 2 o2 sensors should be your next step. any shop can weld o2 bungs near the collectors. it would give a more accurate reading. otherwise you may need some dyno time to get a chip made

 

I think you're right, dual o2 sensors should be on the to do list, and probably the custom tune as well.

FWIW I put the speed density computer in for S&G's, it ran considerably better. I didn't have the shaking and shuddering and popping, but since it did not happen on a regular basis before, I will give it a few days before I make any calls on that. Definetely more low end power with the SD, but the MAF computer sounds way cooler...

Also I called Ford racing tech line, after sitting on hold for 25 minutes I was finally able to ask about the proper plug type and gapping. The guy said to gap at 0.045" to 0.050". I don't know if a few thou are worth worrying about.

The guy just about had a canary when I told him I was using the stock truck intake with the heads. He said the intake ports were too big on the heads and would not seal properly and the reason for my problems was massive vacuum leaks at the intake manifold. I'm not quite sure what to make of that at this time.

Later
Brian

 

The lack of the one o2 sensor isn't gona cause that problem sinse he has the signal from the o2 going to both inputs on the ecm. (i've been like this for about 3 months with out any trouble not even a cel) The custom tune is a very good idea, and the second o2 should be on the to do list but it isn't urgent.

If there was a massive vacuum leak the truck would run like a bag of smashed ***.

 

I can see how one sensor instead of 2 would confuse the ecu, if it tries to change A/F ratio on one bank and doesn't get the proper results. I also wonder if the switched injector wiring due to the firing order differences compounds the problem.


yeah, that's kinda what I thought too. I guess I'll have to watch for vac leaks as time goes by.
Brian

 

I'm tracking a similar issure with my 1990 351w conversion. I have a misfire/sputter that has tempted me to drive her off a cliff! I replaced all sensors, EGR, checked and rechecked timing, changed plugs, wires, checked for vac leaks, and still have the sputter. It is not there when eng is cold and gets progressively worse as eng heats up.

The common thing I see with your thread is the canister purge solenoid! I get code 565 which says the same thing. Problem is, my wiring harness is from the old 302 which did not have the solenoid. I didn't think it did much to the eng performance but now I'm thinking maybe this could be the problem. Even if I buy the thing, I can't hook it to the harness. I've tried everything else and it looks like you have too! Maybe this little $20 part is the problem.??

 

I think you can forget about a massive vacumn leak causing the problem. If you are getting 15-18 lbs of vacumn with those heads and cam then there is no major vacumn leak. Thats about all the vacumn you are going to get.

 

Which PCM are you using? I've been looking more into how the ECU operates the engine the last few days. I would guess if you're using the 302 computer the incorrect CID setting is causing most of your problems, since CID is used in determining injector PW. The fact that it runs better when cold, like mine, makes me think the adaptive control can't compensate for the changes, in your case a bigger engine.

I'm going to test a few things next week. My guess is that my engine "kicks in" when I push the gas pedal just enough for the ECU to decide to go into WOT mode, or open loop control, which is what it does when it's cold.

How does yours do when you mash the gas pedal once it's warmed up.

I think custom tunes are in both our futures...


I don't think that has anything to do with performance since it only allows some gas fumes from the cannister to enter the intake manifold. Once the majority of the fumes are sucked in it becomes a slight vacuum leak. I haven't gotten around to trying this yet but my guess is that a properly valued resisor between the CANP output to ground will make that code go away.


I agree, but then again the rebuild is still so new it might just be a problem waiting to happen after enough heat/cooling/expansion/contraction cycles. I'll think I'll keep some extra gaskets around just in case.


Brian

 

I have since figured out my problem and it had nothing to do with the Canister purge solenoid! My spark plug wires were bad! Just by chance I was under my hood at night and saw nearly all my plug wires arking to the headers. She was really running like crap and misfiring. The wires were less than 2 months old.

Put new plugs and wires in and she runs great.

You might want to look under the hood at night and see if your plug wires are arking. I spent all my time looking for the problem during the day and never saw the arks.

 

thats a nice way to describe my current engine.