My buddy is looking at buying a '91 F-350 with a 7.3 from another friend; it is making a noise that we are somewhat concerned about. I have done some searching and poking around and have not found another thread quite like this, so I thought I would see if anyone can offer some insight.

The engine makes a ticking noise which seems to be coming from somewhere near the #1 injector; it increases with RPM's although it gets harder to hear as the engine gets louder. It does not really sound like a lifter or valve noise; it has sort of a squeaky sound to it. The noise goes away when we loosen the fuel line on the #1 injector; it also goes away when we loosen the line on #8 (before #1 in the firing order, as I understand it). It seems to get louder when we loosen the line on either #3 or #5, if I remember correctly.

We suspected the injector, so we pulled the #1 and #8 injectors and tested them; they both open early and should probably be replaced. The #1 injector would squeak loudly as it opened, so we thought we had found our culprit; however, we switched the two and reinstalled them, and the noise did not move - still seems to be coming from #1, still goes away when #1 or #8 is loosened.

At this point, we are suspecting the injector pump as the source of the noise; I am assuming with 128k miles the injectors could all stand to be replaced as well, but we would like to know where the noise is coming from before he sinks too much money into it.

Any theories or suggestions of other things to try? Neither of us was in the mood to be too scientific with our diagnosis today, so I am open to any ideas on how to narrow it down.

 

A injector pump usually won't go bad just for 1 line, so I'd say the injectors are done. Even them switching them around won't do much, they're all worn.


At 128k it's time for a full time up, injectors and IP.

 

Sounds like BOTH #1 and #8 are bad, if they pop early they are hanging open too long and not atomizing the fuel causing the dead tick you hear.

 

Thanks for the feedback guys. I talked to my friend today; he is already figuring on a reman IP and new injectors if he buys the truck. I suspect that will clear up any fuel system issues. It also needs rear brakes and a FIPL sensor, so I think he has some ammo to negotiate the price down! It is a solid truck overall, I think with a little TLC he should be able to get a lot of use out of it.

Thanks again for the help.

 

Fast-forward almost two years. My buddy didn't buy the truck when I posted about it before, but it's for sale again at half the price and he's pretty well committed now.

In addition to the funny ticking/hissing noise, it has always had a serious oil leak from the right front corner of the motor; we were suspicious that the valve cover had been over-torqued and bent, causing it to leak. He pulled the alternator and bracket the other night to get a better look at what was leaking; what he discovered is that the head gasket is the source of both the leak and the tick/hiss. The alternator bracket had been catching all of the spray and deflecting it down; with the bracket out of the way, the leak spray-painted the front of the engine compartment with oil.

So, now that we know what we're dealing with, here's the new question: is it practical to pull the right head off with the engine in the truck, or would we be better off just pulling the motor to fix it?

 

You can pull the head in-truck, just be aware they are HEAVY. Some use an engine hoist to remove and reinstall.
I don't know about the '91, but on my '86 I removed half of the heater/ac box under the hood, it gave me more room to work on the head.
If you're careful you can reuse the intake gasket/valley pan.
No need to remove the IP to pull the head.