[erik49051]

1990 F250 7.3 IDI 265,000

I have been asking a lot of questions and you all have been very helpful. I want to re ask this question in a thread of its own.

I started noticing a rough idle and discovered an issue with the valves, low compression on #8. Decided to do a valve job. Had 7 bad valves and a severely worn guide on the #8 cylinder. Got it all back together and I still have a rough Idle. The injection pump is fairly new and the injectors are newer. I cracked the lines at the injectors and they all seem to effect the idle the same. Almost no smoke at all. The little I notice, black, is when you get on it.

I have two different brands of injectors, 4 from a diesel shop and 4 from autozone. Could this be the cause?

I haven't checked the compression since the valve job but I don't see any blow by so I am assuming its OK.

I have the timing mark set about 3/4 line advanced.

Any suggestions?

 

[cdnsarguy]

What is the hot curb idle set at........

Auto trans in gear........ 650
Manual trans in nuetral........650

 

[erik49051]

By the tach on the dash 750

 

[drinkypoo]

Matched injectors are preferable but not critical. Bad injectors WILL cause rough idle and may cause smoke. A little black smoke when you are running at load is normal. The timing mark is a ballpark kind of thing; in order to measure timing you need a checker box with a magnetic pickup and a piezoelectric pickup (7.3 method) or a timing light adapter with an optical pickup that replaces a glow plug temporarily (6.9 method... works on 7.3 though supposedly, I haven't tried yet.)

 

[erik49051]

I am going to do a compression test, if ok then I will adjust the timing a little, if that dosent help then I will pull all the injectors and have them tested and matched as you recommend at the diesel shop. Sound like a good plan?

If that same cylinder still has low compression, you will see a grown man cry!

Is it possible to have low compression without blowby?

Thanks for the help!

 

[drinkypoo]

Unless an injector is seriously hosed, it shouldn't affect your compression unless it's improperly seated.

Does sound like a good plan, though.

Low compression pretty much equals blow-by. There is always blow-by...

 

[erik49051]

Thats what I thought, bad valves also cause low compression, wich I had and fixed. Blow by seems very minimal, at least by observing the oil fill tube while running. I can feel a slight suction when I place may hand over the fill tube.

 

[drinkypoo]

Thats what I thought, bad valves also cause low compression, wich I had and fixed.

Yeah I actually read your post I know that sort of thing is not in style but...

 

[LMJD]

You can have low compression without excessive blowby due to bad valves or carbon under a valve and seat (which should not be your case) or due to a head gasket leak. Low compression with excessive blowby would be broken, stuck, worn piston rings, scored cylinder wall/piston skirt.

I will pull all the injectors and have them tested and matched as you recommend at the diesel shop.

A diesel shop won't match them, they'll check to see if they're within specs, you have to take them to an injection shop and pay for extra labor. Without looking up the specs, IIRC the popoff pressure has to be within a 150-200PSI range of each other for a perfectly running engine. Pop off pressure is somewhere around 1600-1800PSI, and a diesel shop can determine that. Some forum people have decided they have to be individually dis-assembled and matched, but any diesel mechanic, injection pump shop guy, or engine shop manual will tell you you're good to go if all injectors whether old or new are in the proper range and your spray pattern is correct, otherwise they need replacing.

 

[erik49051]

Thanks. Will do some checking and post the result.

How durable are the injectors? My helper dropped one on the garage floor.

 

[LMJD]

If it hit directly on the nozzle that's possibly big trouble. If it hit on it's side or top, no big deal. If in doubt you might check out the tip with a strong magnifying glass. The spray holes are very tiny and you wouldn't want to smash one closed.

 

[erik49051]

Compression test is good! All at 450psi give or take 10 psi. Injectors to be tested next.

 

[erik49051]

I'm getting frustrated!

Injectors tested good. Diesel injection shop in St Lous Taylor Diesel recommended replacing the gromets on the fuel line from the filter to the pump. Did that and it seemed to Idle better. Drove to Tulsa, developed a fuel leak, replace cracked fuel line, still running rough.

What to look for next!?

 

[cdnsarguy]

Do you have the fuel line clamps on the steel lines in the correct places...... which line cracked.

 

[erik49051]

Not sure what you mean, "clamps on steel lines"? What clamps on what steel lines? Please explain.

It was the #2 cylinder injector line that cracked.

Doing a clear fuel line test next to see if air is getting in, if i can find the right size fuel line.

Thanks for any suggestions you might have.

 

[chuckster57]

Not sure what you mean, "clamps on steel lines"? What clamps on what steel lines? Please explain.

It was the #2 cylinder injector line that cracked.

Doing a clear fuel line test next to see if air is getting in, if i can find the right size fuel line.

Thanks for any suggestions you might have.

Pete is talking about the line clamps on the lines from the IP to the injectors (sorry for the fancy text, Photobucket editing):

 

[erik49051]

Did the clear fuel line test, no air bubbles. I connected the clear line from the bypass rail up to the filter. It did drain back to the bypass line when I shut it off. Is this normal?

 

[chuckster57]

I haven't done the clear line test to know what it normal, but I believe the line should stay full of fuel when you shut it off. I would guess that you have an air leak somewhere in the return system. I would maybe take another look at the caps for deformaties, or the "O" rings..air can get in where fuel can't get out.

 

[erik49051]

Really, I could have an air leak without a fuel leak? That really complicates things!

 

[erik49051]

I have a video of the engine ideling. How do I post it? Maybe my wifes right, I shouldn't expect perfection out of 20 yr old vehicle? It just bugs the crap out of me though!