Mudman604

i have a 87 f150 short bed short cab 302 4x4 np435. i found out the engine is a HO 302, based on it having the firing order of 13726548, instead of 15426378. the engine has an odd kind of misfire or skip that is audible while idling. otherwise it runs decent, good power ext. but as far as i can tell the efi system is still the 87 system. i was pondering if the ecm is firing the fuel injectors with the standard firing order, not the HO firing order, and if this could cause this small miss and be cause to some efficiency issues. what do any of you think? if this is causing an issue, are ther any sort of extensions for the injectors i could use to re-order the 4 injectors i need to? thanks

Steve83

It isn't. They're bank-fired in that old MFI/MAP engine; only the '94-up SFI/MAF engines fire one injector at a time.

Mudman604

OH, I hadn't heard of that before. I also took the starter off earlier today to find the casting to be F1SE-BB, making it a 91 engine. What do you think could be cause this skip at idle? The tps is good I checked it with voltmeter, distributor has been replaced, it's really clean inside, the cap and rotor I just replaced, wires are good and the plugs are new. I know it's hard to tell from just a little bit of info but I have reached the end of my knowledge and just asking what I can investigate next.

Steve83

No, that makes the casting a '91 design. They might have used that casting past '97.There are too many possibilities right now for me to spend time listing them. If you want to narrow them down, read this caption, study your truck carefully, and put ALL its details into your signature:


(phone app link)That doesn't mean much. New replacement parts are generally INFERIOR to originals (even originals with 300 Kmi). When/why/with what (brand/PN/source) did you replace the original? Did the replacement pass the same test that the original failed?Every bit of info that can go into your signature.

Mudman604

sorry for the delay, got busy and i finally have some time to sit down.

I did not replace the distributor, it was replaced by a previous owner.i would guess when the engine was put it but no telling. it appears new/replaced due to the firing order being rotated clockwise one peg, and it is very clean on the inside.

i pulled the codes and come to find out the TPS did fail, telling the computer full throttle all the time. i fixed that and it warms up properly now.

i still have the little misfire at idle, would the next thing be to get a quality distributor and install or have it installed 100% properly? or could it be something im just going to have to put up with? haha

Chris_1

iTrader: (1)

If it's misfiring there's a reason. Not real likely to be the distributor if it revs good.
Check the plugs; test the wires; do a compression test. bad injector, bad valve ? Learn to test things and troubleshoot the problem. Replacing parts to see if it fixes things is a very expensive way to approach a problem.

Leonardo Mucherino

have you fixed the fault ???

Mudman604

Well, I found out that 3 of the cylinders had around 85 psi, while the other 5 had 160 :/

Then the engine sheered the distributor gear, yet the mechanic could not figure why, so I had the savings,

I ended up putting a new 302 HO long block crate motor from blueprint engines. Runs excellent, did not realize how much power I was lacking.

Anyway, bought new distributor assembly, and I still have a random mis at idle, does not happen all the time, probably about one in Every 4th stop light. And dime times it misses a bit harder under low acceleration, like the engine looses spark for an instant. with MSD Blaster coil, new TFI module and distributor, wires, everything I'm stumped.