91 F250 7.3L IDI miss- cannot figure it out

[Antigrav1117]

Over the course of a week the truck developed a miss, injectors tested 1800-1900, except (2), one was 1400, one was 2400 (***?) lol. So- I replaced the injectors. No change. Cracked fuel lines, discovered (as you face the engine) front left cylinder was the miss. Given (1) the fuel spurt seemed much weaker than the others, and (2) the compression test showed 400psi, I replaced the IP, dialed in static timing, bled the lines, fired it up. Front left cylinder STILL HAS THE MISS! Runs damn good otherwise- for sure I had a worn pump. But now I'm stumped. Could I have a damaged rocker arm? Bent push rod? Bad lobe on the cam shaft? That's all I can think of...

 

[Thewespaul]

Youve ruled the fuel system out mostly, Id pull the valve cover off.

 

[Antigrav1117]

Passenger side valve cover- looks like a bear...or maybe it'll come out without removing the fuel filter housing?

 

[Thewespaul]

Its a lot easier with the housing out of the way but you can pull it just by removing the filter

 

[Antigrav1117]

Pulled valve cover. Cyl#1 is my issue-found absolutely nothing wrong. Springs good, pushrods look and feel good, rotated engine, intake and exhaust rocker arms seem to move completely through their cycles- that's relieving- that at least suggests the cam shaft may be ok. So- I'm back at square one, except I have new injectors and a new IP pump (which, to be fair- makes the truck run NOTICEABLY better- if only on 7) my pump was clearly worn. Sigh- what's next? I guess I start over and re-assess my symptoms.

 

[gandalf]

Where did you buy the injectors and the IP? That can make a huge difference. Not all retailers are equal.

 

[Antigrav1117]

Injectors and IP bought from Pensacola Diesel. I'm considering that as a very low possibility, because the basic symptom did not change after these parts were installed. #1 cylinder not firing. Ha- can't positively rule em out, don't have a way to test the IP cylinder one shot. But #1 injector tests exactly like all the rest, has a good pop and spray pattern.

 

[Antigrav1117]

Is there any way- that the little pick up unit on #1 for the clamp used to set the timing could be causing this? It's an odd little piece, only on cylinder 1. You can blow through it, but if there was some kind of bladder or expansion chamber in it that could defeat the IP pulse... hell I'm fishin I know...

 

[Antigrav1117]

Ok, so back at square 1, I've ordered a couple extra injector lines, gonna pull #1 and use the extra line as a test line, put an injector on it and see if it pops it and flows. That will at least verify fuel delivery, and positively test the IP output for that cylinder.

 

[Thewespaul]

The timing adapter won’t affect anything, Pensacola is known for less than quality parts, ill let others fill in the details
With engine idling, crack injector line 1 and 4. They should both be seeping a similar amount of fuel, if not the pump is bad.

 

[Antigrav1117]

Ok- so here's what I did. I ordered a spare #7 & #8 fuel line. I removed #1 fuel line from IP (problem cyl) and found that the #8 worked perfectly as a test line, came up above the engine where I re-installed a spare injector (that I already tested opening at 1800, the fuel return cap and with a single piece of hose, reconnected the return lines. Oh I also added the pulse sensor on the test injector. Guess what? the IP pump works perfectly. Squirt Squirt Squirt. So- if anyone ever needs to, this is a valid test of the general health of the IP, as installed on the truck. Fuel is being delivered. And- since the pump only has two injection pistons, and the other 7 cylinders all operate- the quantity of fuel pretty much has to be correct. Not a lean nor a rich burn- zero smoke.

So- my last question. I have to make a trip of 80 miles, one way. What are the risks with driving it anyway.

 

[Thewespaul]

The db2 has two plungers, but it has 8 different passages in the head for each cylinder, yes the injector is firing fuel but it doesn’t mean that delivery is in time with the others, which would cause a misfire. If it want delivering fuel at all it wouldn’t misfire, you would just have a cold cylinder.

 

[Antigrav1117]

Don't know where you got MISS-FIRE from. It's a MISS, as in cold cylinder. Pretty sure you cannot "time" a difference between the pump outputs, as these are all milled metal parts. Not adjustable- insofar as I can tell. Thanks anyways.

 

[Thewespaul]

If there’s an issue with any of the passages in the pump’s head for each cylinder then the timing could be off for that line. It would have to be very off for it to be a cold cylinder, but it’s possible. Especially since the pump came Pensacola I would lean towards that being an issue. No these pumps are not just milled metal parts, take one apart and read through a service manual you will learn a lot.

Do you have any chuffing out the exhaust? Does the cylinder ever get heat in it or is it always cold?

 

[Antigrav1117]

Ok everyone- truck is fixed. Turns out- I had a cracked fuel line. Couldn't believe it. #1 line developed a severe leak- I thought I had damaged the face, so I resurfaced the "cone"... if you take your time, this works, the face is pretty malleable and will, upon compression, re-develop a sealing "face". However after carefully resurfacing, and re-installing, it was quickly evident that I still had a major leak. So I tightened the nut as much as I dared, still leaking...so I pulled on the tube, absent minded like, and pow- the tube came out, minus the end!!! Now what!?!? Fortunately, the #8 line I had used for a test line was long enough, so I took 2 hours to re-bend it to fabricate a new #1 line (minus the timing sensor). Re-installed and WOWSA - we hittin on all eight!! WOOHOOOOO freakin cracked line. Funny I didn't even see fuel coming out before it got really bad...I guess it was just sitting in the nut...