7.3 idi turbo missing/bucking and weird exhaust pop

[DeadSlowAhead]

Hi all, first time poster and newer member. I’ve got a 1992 f250 7.3 IDI turbo ZF5. Truck is acting up and steadily gotten worse, but what is weird is the issues get worse when hot. Noticed truck misfired intermittently at low RPM, but went away. Now truck starts fine, surges a bit right around 1500 when cold, but when warm it bucks/shakes and when letting off throttle it falls a bit below idle and stutters for a second then comes back up. It has also started popping out of the exhaust intermittently at idle when warm, about every 5 seconds it’ll pop. My main thought is air intrusion, but it’s been rock solid for months. I’ve ran new supply lines from FSV forward and have an electric lift pump. I have 240k miles and as far as I know the injection pump and injectors are original, so I’m prepared to change those. I am away for a work trip so can’t test anything for a week but any insight is appreciated. I can’t seem to attach a video of the exhaust pop but I do have one.
Thank you all,
Rohan

 

[Nero]

If the fuel pump and injectors are original, theres a good chance they are worn, but probably not the culprit. Last time I heard one like this it was a loose valve guide, pull the valve covers and see if one is notoriously dirtier than the other?

 

[DeadSlowAhead]

Nero,
Thanks for the response. I’ll definitely pull those when I get home and take a look, thank you

 

[IDIBRONCO]

Last time I heard one like this it was a loose valve guide, pull the valve covers and see if one is notoriously dirtier than the other?

This was my first thought as well. The problem is that it happens about once every 5 seconds on a warm idle. If it was valves guides, I think that it should happen more often. I'd still lean toward the fuel system. I know that these don't all sound like fuel system problems, but with 240,000 miles, who knows? I remember one rebuilt IP that I put on that sounded like it had an injector knock. We tried diagnosing the noise and got to the cylinder where it was coming from. I replaced that injector, still there. Replaced the one before and after it in the firing order, still there. Swapped injectors around, still there on that cylinder. Replaced all of the injectors, still there. Pulled the engine and put in another reman engine with the same pump and injectors, still there. Finally, I swapped IPs and the noise was gone. It was sent back to the rebuilder and the only answer we got was "it was a bad crush washer". After all of that, I agree that it still wouldn't hurt to pull the valve covers and look around. Be sure to check all of the rocker arm bolts while you're there too. One could have come loose or broken (don't ask me how).

 

[DeadSlowAhead]

IDIBRONCO,
Thanks for the help.
New injectors are on the way and buying an injection pump soon. Hopefully a R&D if they got one in stock, otherwise a moose pump. I’m gonna do testing for air when I’m back but the fuel system is definitely worn and in need of replacement.

 

[DeadSlowAhead]

This was my first thought as well. The problem is that it happens about once every 5 seconds on a warm idle. If it was valves guides, I think that it should happen more often. I'd still lean toward the fuel system. I know that these don't all sound like fuel system problems, but with 240,000 miles, who knows? I remember one rebuilt IP that I put on that sounded like it had an injector knock. We tried diagnosing the noise and got to the cylinder where it was coming from. I replaced that injector, still there. Replaced the one before and after it in the firing order, still there. Swapped injectors around, still there on that cylinder. Replaced all of the injectors, still there. Pulled the engine and put in another reman engine with the same pump and injectors, still there. Finally, I swapped IPs and the noise was gone. It was sent back to the rebuilder and the only answer we got was "it was a bad crush washer". After all of that, I agree that it still wouldn't hurt to pull the valve covers and look around. Be sure to check all of the rocker arm bolts while you're there too. One could have come loose or broken (don't ask me how).

Like you said, the popping is not in time with the engine firing. Could a bad/failing injection pump cause surging and bucking?

 

[IDIBRONCO]

Could a bad/failing injection pump cause surging and bucking?

I sure can't say yes, but I can't rule it out either. I think that the best test for that is replacement. Then you'll know for sure.

 

[DirtyWood]

Do you hear any light ticking in rhythm with the engine?
I'd break out the stethoscope and start poking around.

 

[DeadSlowAhead]

Do you hear any light ticking in rhythm with the engine?
I'd break out the stethoscope and start poking around.

I haven’t heard any ticking but have not really listened for it. I am sure my injectors are shot and probably pop at all random pressures with their age and mileage. I’ll take a listen when I’m back home. Thanks.

 

[DeadSlowAhead]

Do you hear any light ticking in rhythm with the engine?
I'd break out the stethoscope and start poking around.

DirtyWood,
Finally got home and started messing with it. No ticking but after running it for a while it will barely stay running. Takes more cranks than it should to fire off, kinda like there is air in it, but throttle response is horrible and it had a lopey idle now. I don’t think it’s air but I got some clear fuel line I am going to throw on tomorrow. Also going to fill it with ATF and let it sit in case the pumps insides are gummed up, but I’m leaning toward injection pump replacement.

 

[IDIBRONCO]

Have you tried advancing the timing? That sounds an awful lot like how the used pump I just put on mine was acting. I advanced the timing as far as I could without loosening the lines and it is better. I'll have to loosen the lines and advance it some more.

 

[DeadSlowAhead]

Have you tried advancing the timing? That sounds an awful lot like how the used pump I just put on mine was acting. I advanced the timing as far as I could without loosening the lines and it is better. I'll have to loosen the lines and advance it some more.

I advanced about a dimes width 6 months ago and made a pretty big difference. I’ll try and do it again, it’s free rather than $1000. I noticed the RPMs also take a while to come down when I rev it in neutral.
This is my first diesel and IDI, and while I’ve been learning a lot I really appreciate the help.

 

[IDIBRONCO]

You may be able to limp it along for a while longer so you have time to save the money for new parts. If it's hard to turn, you may have to loosen the injector lines where they come out of the pump. It is a task. You'll need a crow's foot to get to the lower lines.

 

[DeadSlowAhead]

Advanced timing, it sounds better, a little bit of rattle but sounds healthy but no improvement in idle. Swapped injectors and they were stamped 1991 so they were original. Injection pump had a similar date stamped on it so pulled it and ordering a new one soon. I am still going to test supply/return with clear fuel line to look for air but seems like worn out fuel system parts with 240k miles on it. She’s been neglected a lot so it’s needed to replace these parts. Injectors looked pretty bad with a lot of carbon buildup and injection pump leaked out of a few places.