For the last 2 days I've been diagnosing a 99 F-250 7.3L. when driving and idleing the truck has a misfire. When idling there is a blaitent misfire (or at least it thought) and when driving you can completely tell that there's a miss. No active codes so i did a cyl cont test. cylinder 8 came up. Usually when i run into this i'll just sell an injector, that way I can get into the valve cover and test the injectors and the valve cover gasket. however, i know im not supposed to do this because of the potential danger but i go down the head and unplug injectors while running to see which one doesn't make a change in idle. On the d-side of the engine, all made a noticable change in idle when they were unpluged. Hmm i though...I proceeded to the p-side valve cover. Tested gasket harness and did the unplug test. Same results! Hmm again i thought. The engine has a obvious miss, but all cylinders make a change in idle.

So I went ahead and just replaced the #8 injector with one i had. No change in idle. i checked the oil for fuel, none. All glow plugs were tight and none were leaking compression. So I proceeded to a compression test. All cylinders do 300psi, that is on the engines 5th compression pump (might be 4th, but all were tested the same amount of cranks). So compression is good, what now.

I then whipped out my Vantage and hooked up to the COM wires at the v/c harness. All cylinders had identical voltage at idle. I then swaped the v/c gaskets from the p.side to the d.side, no change. There are no loose (overly at least) rocker arms and no popping out of the intake or exhaust that might suggest a burnt valve. No smoke either! I've seen injectors go bad before an wash cylinders but this isn't like those.

On to the "out of place" things: Someone has been in this thing and replaced 3 injectors with AA aftermarket injectors. As im sure we all know those are supposed to be for the 94-97 PSD's and the 99-03 need the AB's. Cylinder 8 when unpluged makes less of a change in idle than the other cylinders do. Yes, I do have an AE injector in number 8. Also the vehicle has a long crank, about twice as long as it should be.

So what im leaning toward is either a bad PCM or IDM, whichever does whatever, or some sort of internal oil pressure issue/fuel issue. I replaced all o-rings and put on a new seat washer. There is no odd crankcase pressure either and the cranking when starting is smooth.

Thanks in advance for any help and reading my essay. I will check tomorrow on the CPS color.

 

What year is the truck you're working on? If it's 99.5-03, it should have ADs in all but 8 which MIGHT have an AE. Early 99 had ABs. However, AAs are single shot injectors, IIRC and will screw the idle up. I'd say put them all back to ADs or ABs and go from there...

 

It takes custom tuning on these trucks to run single shot injectors or you end up with a cam lope idle as Joe said. If you try and mix split shot and single shot injectors, plus throw in a long lead injector in #8, I don't thing there's any way to get it to run right.

Like Joe mentioned, 99.5 - 03 trucks came with the AD injectors with an AE in #8. Did the AA injectors not show a different reading on the contribution test?

 

Not all late trucks have an AE in the no. 8 hole. Some got built that way, some had it added after complaints of cackle...

 

Should have done that first.

Early 99's came with AB's, 99.5-03's came with AD's.


NEVER mismatch injectors. If there are 3 AA injectors in there with AD's, get them out now.

 

Nothing other than cyl 8 on the contrubution test, buzz test was also clean.

This is considered an EARLY 99. The build date is mid-late 98 i think, I'll confirm tomorrow. I wasn't too concerned about the CMP sensor because of the dead miss. True, it is a rough idle, but its not like its a random cylinder miss, or how the 6.0's idle when the egr gets stuck open 10%, its a dead miss. The AA injectors that are installed are aftermarket by a company called ITS i think.

However is this the solution to my issue of the "ghost" miss? it seems that when i disconnect those injectors they make a huge running difference compared to when i disconnect cyl 8.

Is it possible that the IDM or PCM is cooked because of this?

Other than the mechanical difference, how do the AA, AB, and AD injectors differ from eachother as far as the computer is concerned? i.e. timing, duration, pressure, volume, voltage, etc...

thanks again for all the help!

 

If AA and AB injectors are mixed in there, then yes it's going to run extremely rough. AA's are single shots, AB's are splits. It requires completely different tuning to run each type of injector. Stock early 99's run AB split shot tuning. So trying to run singles on split tuning results in a bad idle.

First step is to ge the AA's out. They are smaller (CC's) than the AB's anyway, so it's not only causing the truck to idle poorly, but also to lose power.

Second, once all the injectors are matched, then look at the CPS. If a grey one is in there, ignore any cylinder contribution faults until it's replaced with a black one. Then re-test and see if there are continuing problems.

 

What Curtis said.
Get all the injectors matching with the same code and take it from there.
There is no way possible to get the engine to run right until the hardware matches.

 

cool, thanks for all the insight so far. I sold 3 AB injectors to replace the AA injectors in it. What aftermarket brands of injectors are the best? I've always installed the rebuilt OE ones from Ford and Alliant Powers. The brand of AA's that is in there now are a brand that i've never heard of before called ITS. They have a green top as well and a part number very similar to OE (it starts with AA). Has anyone ever heard of this brand?

I'll probably get those injectors installed monday, since saturday is always jamin'. I'll try to keep updates coming once they're installed. Thanks again for all the help.

Oh, almost forgot the drama....apparently Ford replaced the number 3, 4, and 6 injectors on this bad boy 2 years ago and odly enough, the injectors with the aftermarket ITS injectors in them are 3, 4, and 6. There's something to ponder....

 

I'm not an injector guru, but I know Alliant is the go-to place for OEM replacements. Never heard of ITS...

However, you can probably get upgraded remans for the same money or cheaper, depending on the injector. Is this your truck our a customer's?

 

its a customer of mine. He usually comes here for front end work and LOF's. But when he learned that we do everything on 7/3's and 6.0's (because we all own them) he decided to give us a crack at it.

 

Find out what the customer wants. If the customer just wants to get it running right, buy 3 new AB's and throw them in and you can call it a day.

If the customer wants to upgrade, find out how far he wants to go. Because any upgrades to the injectors will require other supporting mods (tuning, turbo, transmission, etc). It gets expensive fast, especially on an early 99 truck.

 

Do this first!!!

 

I think he could go with all ADs and be safe, but y'all are right -- see if the customer wants to bother. Does the early NEED the AE in number 8? I *HATE* mine right now, but then again, I have the mods in place where I don't need it.

 

I told him thats where i'll start and then we'll go from there.

Would you still need custom tuning if you went to all AD's in a 99-03? (and one AE of course)