I have a 1990 F-Super Duty with the 7.3 IDI; I recently (2 weeks ago) put all new Delphi injectors in. Today while the truck was going down the road, atleast one of the injectors went bad or is sticking. Blue smoke out the tail pipe, bad knock on the top of the engine, and the unmistakable smell of raw fuel in the exhaust. It's not as bad at idle as it is when at running speed. I could be wrong but it appears to be a new injector gone bad.

I have not replaced the I.P., that will be done when I get the money.

I am looking for an easy way to isolate the bad injector and replace it with out replacing all 8 injectors again.

 

Stethoscope. Touch it to the nut that connects the fuel line to the injector and you will hear the knock on the bad injector. You can get the scope for like 3 bucks at orielly auto parts. Good luck

 

You could also try cracking the fuel lines at each injector to see if you can notice a change. You will get a little fuel on the motor, but not much.

 

Thanks, I like the stethoscope idea, i will give it a try first, if that doesn't work then I will busting the injector lines loose.

I think i know the answer, but I am going to ask the question anyway; is there any chance the I.P. is causing the problem? I personally don't thinks so, but I am not willing to rule anything out yet!!!

I bought this truck in september, overall it has been a good truck. I wanted to change out the injectors before we got into the Florida summer and the A/C running all the time. I have done injectors before on my '91 F-SuperDuty. FOr those of you keeping score at home, I have two, A 1990 and a 1991. I wish I had just put a new engine in the 1990 when I bought it, it took 2 days to get out four stuck that seperated the top from the bottom sleeve in the injector bore. I finally figured out my own trick that works really well, too bad it took 2 days to think of it!!!

All 8 had carbon build up, but the four that separated were the worst. I took an old injector and ground off the large threads, threaded it into the lower sleeve, soaked the injector with seafoam to loosen the carbon, then soaked in PB Blaster. I then using a cordless impact, spun the injector clock wise while gently pushing up on the injector under the socket. The injectors walked right out!!! I thought about a slide hammer, but you can not get it on #7 or #8.

 

If you put in new injectors in a worn out pump your timing is going to be wayyyy off....white smoke I would advance the pump...

 

I've been in a similar situation, turns out I didn't get one of the injectors screwed in all the way and it separated in the middle. It eventually would not start, period. If you think it is a bad injector, I would suggest to pop test them. It's simple enough to do, I have pics of the process if you need them. As for the IP, I would do that relatively soon, best to do them in pairs, but new injectors won't destroy it right away unless it was in really bad shape.

 

After youve had it running a bit, the injector line to the bad injector will be hotter than the others too.

 

Oh something else I remembered is that if an injector isn't firing correctly, over time it will cause the glowplug on that cylinder to go out. You can test those with a light tester. Positive to battery, ground out at the glowplug post. No light, bad glow plug.

 

Not sure i would trust that

 

I found the method on this forum and it worked for me, found one bad glow plug. Don't try it if you don't want to.

 

I didnt mean to offend, but i dont see a miss-firing injector taking out a GP, i suppose its possible. But really what i was getting at, the odds of having a burnt out plug just because its burnt out vs. the plug at the bad injector could still be working.

Easiest way to do it is crack lines until the knock goes away... same deal as pullin the plug wire on a gasser to find a miss. Can tell you a weak cylinder, missing cylinder, if you have a rod knock, which hole its in etc etc.

 

No offense taken, I should have been more specific too. It's more to identify if an injector is under the spec pop off pressure, from what I understand it doesn't burn the fuel the way it should and cause the glow plug to go out. I'm not sure if that's 100% true, I read it here, but the light test is definitely a way to find out if they are bad or not. I hope OP figures out what is going on though.

 

Well here's an update; I got a stethoscope, and tried to listened to all the injectors, I failed at it as I really wasn't hearing what I was looking for. I also have a case of diesel ear. I moved on and cracked all the fuel lines one at a time, turned out it was #7. I replaced it with another new injector, and re did o-rings. I am starting to think this engine is tired, and may need replacing, I am going to try to make it through the summer and then rebuild it or put a rebuilt one in it.

 

Hmm... how many miles are on this motor?

 

You just asked the million dollar question; First off this is not a personal daily driver, it's an F-DuperDuty Flatbed tow truck. I bought the truck in september of 2012, and the place i bought it from claimed there was only 70K on a ford rebuilt done by a dealer. I knew what I was buying, and I paid a great price for this type of truck, ($6500) so I am not complaining. I have seen the same truck, in worse condition going for double that.

Given the amount of carbon build up in the injector bore, I am guessing the injectors had not been touched in several years. Since I have owned the truck, I have put about 15k on it, I was hoping to extend the life of the engine by doing injectors and then the I.P.

I did replace the G.P.'s when I first bought it, well most of them. I found the #5 G.P. had been broken off clean, and no hope of getting it out with out removing the head. It appears to be rusted in place, I have a picture of it somewhere and will try to post it later today.