Engine Misfire After H/c/i Swap

Landon116 · Mar 2, 2015

Little update : went back over my wiring and found that the #1 and #2 Injector wires were swapped. I verified by wire color. the car runs better but has a misfire still. It runs much better the more I advance the timing. how much timing is typical of the B cam? after I installed the wide band the car stays right around 14.7 at idle and light cruise. if I accelerate I hear the huge miss fire so I haven't driven it. it still sounds like a Rev limiter when it misfires. any more suggestions? the #1 and #2 wires are surprising easy to mistake as they come out of the wire harness at the same place, with a small difference In wire length.

thanks guys

Dave2000GT · Mar 3, 2015

Landon116 said:
Little update : went back over my wiring and found that the #1 and #2 Injector wires were swapped. I verified by wire color. the car runs better but has a misfire still. It runs much better the more I advance the timing. how much timing is typical of the B cam? after I installed the wide band the car stays right around 14.7 at idle and light cruise. if I accelerate I hear the huge miss fire so I haven't driven it. it still sounds like a Rev limiter when it misfires. any more suggestions? the #1 and #2 wires are surprising easy to mistake as they come out of the wire harness at the same place, with a small difference In wire length.

thanks guys

I believe it's most likely spark related. Are the 764s brand new? Tried re-snapping on the wires on the spark plug side?

Landon116 · Mar 3, 2015

Dave2000GT said:
I believe it's most likely spark related. Are the 764s brand new? Tried re-snapping on the wires on the spark plug side?

yeah they're brand new. I just recently got my wide band installed and I discovered that when the misfire happens , the gauge goes to 17. so it is probably fuel right ? I thought it was spark related too until I saw that.. heading towards injectors.

A5literMan · Mar 3, 2015

Landon116 said:
yeah they're brand new. I just recently got my wide band installed and I discovered that when the misfire happens , the gauge goes to 17. so it is probably fuel right ? I thought it was spark related too until I saw that.. heading towards injectors.

"Holy lean condition" batman! Run the koer codes.

Landon116 · Mar 3, 2015

A5literMan said:
"Holy lean condition" batman! Run the koer codes.

Haha, I ran the KOEO and KOER coeds, just emissions codes. AFR is at 14.7 always or richer (perfect) other than when you give it half throttle and it misfires.

Landon116 · Mar 3, 2015

With a 308ci, ported GT40p heads, gt40 upper and lower, b303 cam, 70mm throttle body, 70mm maf (sn95), cold air intake and exhaust do you think the 19#'ers are getting pushed a little to close to their limit? Just wondering if I have a bad injector, I will probably replace the set because they have atleast 175,000 on them I think. I would rather invest in 24# injectors now than waste ~$100 on a set of reman stockers.

mikestang63 · Mar 3, 2015

Your injectors may be maxing out on duty cycle but nothing rasing the fuel pressure can't fix. If they are tired, try dumping a bottle of techron in the tank and see that clears them up.

What do your plugs look like- are they looking lean?

Take a small dowel or mechanic stethescope and listen to each injector. You should hear them click as they cycle open and closed.

And yea, 17 AFR is just a wee but on the lean side. You sure there is no vacuum leak?

A5literMan · Mar 3, 2015

Theoretically the 19's should be fine. But I would probably go to 24's. Also when you say the AFR is 14.whatever is that at idle only? And when you start to give it fuel it goes lean? Also I'd rather see the AFR around 12-13 with a n/a combo @ wot. The computer has different fuel curve from idle to part throttle to wot. There isn't a chip installed correct? What do your plugs look like after driving it at operating temps? If you're getting a AFR reading that lean something is definetly not right on the fuel side of the equation. Make sure all the injectors are working properly. You have the proper pressure readings at the regulator? What pump do you have? What do you have the timing set at? What octane fuel is in the tank? Does it break up at part throttle and clean up at all or just fall on its face?

Landon116 · Mar 3, 2015

Well my idle and cruise after warming up and is in closed loop, is around 14.7 and when you lightly accelerate( avoiding the missfire at half throttle) it stays around the 13.5 range which is just right. I haven't gone WOT much because im afraid of leaning out or detonating. No chip, reman a9l which has worked great for months, plugs have a hint of tan, little lean but just about right, I can hear injectors operating with a mechanics stethoscope, 255 walbro pump, timing is at 14 degrees now because it likes it much better than ~10 degress, running 93 octane. (Same issues with 89) It breaks up at half throttle in second gear mostly or whenever a good load is applied. The more I can learn for this the better, Im still in high school and I recently won state champion in the Automotive Technology competition, im going to compete fixing bugged cars at the national level in NYC in april so the more suggestions I get the more I learn. I have noticed the fuel pressure drops when throttle is applied and I dont think my regulator is working properly , It stays steady at 40psi with vac disconnected, this problem has existed before any of this work. It only drops like 5 pounds but just for safe measure I purchased a Kirban adj. pressure regulator last night, when I install it, injectors will be tested.

Thanks for all the great help guys, I always can turn to Stangnet for these tricky issues

jrichker · Mar 3, 2015

You seem to be familiar with the cylinder balance test. Have you done one using the cylinder balance test built into the stock computer?

Landon116 · Mar 3, 2015

jrichker said:
You seem to be familiar with the cylinder balance test. Have you done one using the cylinder balance test built into the stock computer?

Yes, I have performed the cylinder balance test using the EEC, You know that sound during the test when the EEC turns off an injector to see how well that particular cylinder is contributing ? Thats exactly what is feels/ sounds like when driving the car under load. Except more pronounced. Absolute best way of describing it. I am going to probably test my injectors when I get them off, and most likley use a Noid light to test wiring. Does that sound like a good approach? I have done all of the obvious things on the ignition side.

jrichker · Mar 3, 2015

That sounds reasonable to me. If you got a 90 as a the result of the cylinder balance test, the Noid light probably isn't going to find anything.

I would look closely at the 10 pin connectors and try wiggling the harness and connectors while the engine is idling smoothly. Note any change in RPM or in the sound of the engine.

See the graphic for the 10 pin connector circuit layout.

Landon116 · Mar 3, 2015

jrichker said:
That sounds reasonable to me. If you got a 90 as a the result of the cylinder balance test, the Noid light probably isn't going to find anything.

I would look closely at the 10 pin connectors and try wiggling the harness and connectors while the engine is idling smoothly. Note any change in RPM or in the sound of the engine.

See the graphic for the 10 pin connector circuit layout.

Alright will do, I had to disconnect them recently right before these problems came up to paint the engine bay, So I will definitely have to take a look, thanks Jrichker

Dave2000GT · Mar 3, 2015

Landon116 said:
yeah they're brand new. I just recently got my wide band installed and I discovered that when the misfire happens , the gauge goes to 17. so it is probably fuel right ? I thought it was spark related too until I saw that.. heading towards injectors.

Well your symptoms still point to spark in my opinion. It idles fine, runs fine under light load which means your fuel system is at least capable of delivering the right amount of fuel under some (or all) conditions. Usually bad injectors are bad, and if your injectors, pump etc was fine before it hasn't suddenly gone bad by coincident. Highly doubt your injectors are maxed out, and even if they were, this would be at the TOP end, like 6K rpm after you've wound up to there through 3rd gear. Not when applying heavy throttle mid-way through the RPM range.

AFR is derived from your wideband O2 - which is measuring oxygen content in the air. When you misfire (ie missed spark), there is un-burned fuel but also un-burned oxygen which gives a high air (oxygen) to fuel ratio, so don't let it fool you into thinking it is strictly a fuel issue. In my experience missing under load is usually spark -and this won't show up in the cylinder balance test, since it's not performed under load.

I'd recommend to pull each plug wire and re-apply di-electric grease, but when they are off physically look/feel the plugs to make sure none are cracked etc, maybe remove them to look closer if you have the time. I know they are new but it is possible. Make sure when the wires go back on that they are clear of headers, possible arc points etc.

Landon116 · Mar 4, 2015

Dave2000GT said:
Well your symptoms still point to spark in my opinion. It idles fine, runs fine under light load which means your fuel system is at least capable of delivering the right amount of fuel under some (or all) conditions. Usually bad injectors are bad, and if your injectors, pump etc was fine before it hasn't suddenly gone bad by coincident. Highly doubt your injectors are maxed out, and even if they were, this would be at the TOP end, like 6K rpm after you've wound up to there through 3rd gear. Not when applying heavy throttle mid-way through the RPM range.

AFR is derived from your wideband O2 - which is measuring oxygen content in the air. When you misfire (ie missed spark), there is un-burned fuel but also un-burned oxygen which gives a high air (oxygen) to fuel ratio, so don't let it fool you into thinking it is strictly a fuel issue. In my experience missing under load is usually spark -and this won't show up in the cylinder balance test, since it's not performed under load.

I'd recommend to pull each plug wire and re-apply di-electric grease, but when they are off physically look/feel the plugs to make sure none are cracked etc, maybe remove them to look closer if you have the time. I know they are new but it is possible. Make sure when the wires go back on that they are clear of headers, possible arc points etc.

yeah I was just wondering that if I do happen to find a bad injector should I just go ahead and step it it up? but that's down the road right now... I was thinkin, if I have my wide band sensor mounted on the driver side and the wideband AFR goes lean during the misfire.. do you think that the misfire just might happen to be on the driver side? or do you think that the passenger side is likely doing the same thing ? plugs were the first thing i checked and i did find a bad cracked plug! it was replaced im gonna look into wires thanks again

Dave2000GT · Mar 4, 2015

Landon116 said:
yeah I was just wondering that if I do happen to find a bad injector should I just go ahead and step it it up? but that's down the road right now... I was thinkin, if I have my wide band sensor mounted on the driver side and the wideband AFR goes lean during the misfire.. do you think that the misfire just might happen to be on the driver side? or do you think that the passenger side is likely doing the same thing ? plugs were the first thing i checked and i did find a bad cracked plug! it was replaced im gonna look into wires thanks again

Makes sense, just don't get sucked into the trap of replacing every part. Assume that any part that was fine prior to the swap is fine now.

For sure that points to a misfire on the driver side, now of course if it's distributor/coil related it could be happening to both sides. Are you running stock headers? I've heard that stock headers have good chance of arcing cylinder 7 (drivers side) with gt40p's.

Dave2000GT · Mar 11, 2015

Any update?

Landon116 · Mar 11, 2015

Dave2000GT said:
Any update?

Waiting on some good plug wires , and injectors before I start working on it. I will post the results because I hate it when threads end in no solution or update.

Dave2000GT · Mar 11, 2015

Landon116 said:
Waiting on some good plug wires , and injectors before I start working on it. I will post the results because I hate it when threads end in no solution or update.

Sounds good,
I hate it too when issue threads go unresolved, ideally I'd like to see every thread end in either "Fixed it by doing a, b, then c" or "Got sick of this crap, sold the car"
Makes it so much easier for others to find possible resolutions to similar sets of symptoms.

Landon116 · Mar 25, 2015

Little update: Got some reman flow tested injectors because I didnt like having old 175,000 mile injectors on a almost restored car. Got a Kirban ajd fpr and bumped up the fuel pressure a little ~43 psi. It helped a little with the bad miss but I tried changing around my plug wires because, upon first start I burnt two Ford racing wires and replaced them with shi**y Autozone stocker replacements. I swapped around the wires with a few half burnt (best I had) ford racing wires and the problem seemed to change for the better, or atleast change. So I ordered a fresh set of ford racing plug wires and I should get them soon, sorry for the long wait but Im getting there. Thanks again

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