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Old 02-19-2012, 09:18 PM
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I'm truly stumped.

Hey everyone, new here.

I've been having a very long saga with my friend's early 99 7.3. Hopefully someone will take the time to read all of this and maybe point me in the right direction with things. I'll try to make this as non-boring as possible haha.

Basically, a few months ago my good friend bought a sick early 99 extended cab f250 on brand new 38's, wheels, trans and garrett GT38 among other goodies. Honestly, even if this thing needed an entire motor, I personally think its worth the $4400 he got it for. The reason for the cheap price was that the motor misfired like a mofo. It was down AT LEAST one cyl, possibly more. The guy swore up and down that his mechanic said it was down on compression on a cyl (dont remember which) and needed a HEAD. Motor was still pretty strong for a 7.3 did not lose coolant or oil, although i knew it should still make alot more power. It shook alot at idle, but smoothed out quite a lot when you ripped on it. I should also add that this truck has 170k on it.

So we got it home and got to work. Now guys, I totally realized I SCREWED UP BIG TIME HERE, no need to tell me lol. I was dumb and took the guys word for it, and i was cheap and didnt get the glow plug compression test adapter. I just went ahead and tore into the motor, expecting to just throw a head on.

First I wanted to see if I'd get off easy and it would just happen to be a loose rocker pedestal. Nope, all were tight and no cylinders have bent pushrods or wiped out cam lobes. Damn, onto the next thing, injectors (which one of my friends who owns a diesel shop suggested after hearing it run) the tips looked pretty crappy, but not wasted. All injector solenoids ohmed out to like 3.1 or 3.2 which is good.

So what does my dumbass do next? I RIP THE HEADS OFF turns out, all the crosshatching is pretty ok in the cylinders, headgasket looked fresh as new, and all the valves seal like new Okay, now Im realizing that Im a total moron at this point, but life goes on. Brand new gaskets go in along with valve stem seals (valve guides were fairly tight too). May I also note that on the driver side, 3 pistons were pretty black, and one was clean. Passenger side had 3 clean and one black. None had very clear "star patterns" on top.

So, onto the injectors. We took the risk and bought the infamous ebay 40hp DIY nozzle and o-ring kit. The rebuild went smoothly, and everything looked pretty nice inside the injectors, although a few plunger/barrel assemblies were a little chewed up (possibly a red flag here) and one injector had a really really tight amplifier piston, possibly seized, i couldnt move it myself but maybe HPOP pressure still could? (and what im thinking is an even bigger red flag here). So everything gets thrown back together, and she starts up. It runs *a little smoother* and its *a little quicker* but it still idles like @ss, exactly the same as before, maybe a liiiiitle smoother, but not really. okay so at this point IM PISSED.

Before replacing the one injector that had the tight amplifier piston, and then after that if its not better, doing all of the plungers and barrels, I finally looked into possible electrical issues. I started with a cylinder contribution test. Injectors on cyls 1,4,5, and 7 contribute alot, and give a healthy squirt of oil out of the little exhaust chutes. 3 and 2 barely contribute and dont squirt too much either. Let it be known that number 2 is the one with the suck amplifier piston. 8 and 6 barely contribute as well but seem to squirt. (by the way, my contribution test is just unplugging one injector at a time at idle and watching for a change in rpm/idle quality, not sure about you guys).

Now onto interrogating the IDM as much as possible. I know it's technically not possible to measure idm output with a regular multimeter, but what i do know is the center pin on the valve cover harness with the key on and engine not running should definitely read the same voltage on both sides, and it doesnt. driver side has 4.4vdc and passenger 1.5vdc. that's quite a big difference (and im thinking another huge red flag). Now from what I've heard, IDM's tend to fail by taking out an entire cylinder bank at a time, but the piston color/squirt/contribution tests dont suggest such a pattern. Oh, I also ohmed out the valvecover harnesses and everything came out fine.

So I figured the next step was to get serious and whip out the oscilloscope and check the idm output waveform, injector flyback current, ckp sensor, and cmp sensor. Went out and bought a sweet brand new probe to use with my old Heathkit IO-14 scope only to find out that all the caps had shorted with age and I was beat- no scope tests for me.

So, here I am. I know, I'm a total goon and should have done more research and testing before diving in, and I probably should have just exchanged injectors for remans. BUT that's the past and I'm here now. So should I throw an IDM at it? Any other tests I should try first? I'm really pulling serious hairs out over this. If anyone has ANY suggestions, I would appreciate it SO MUCH.

Thank you for taking the time to read all of this!


Last edited by zukirider21; 02-19-2012 at 09:25 PM.
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Old 02-19-2012, 09:31 PM
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Man that is alot!!! Lol


this almost seems like a waste to suggest and i dont mean to insult but have you given any thought to the CPS? Seems like guys have similar symptoms and it is the culprit.
I too would be suspicious about that injector with the plunger hanging up especially since it isnt pumping as much.

Was this a stock engine when you got it besides the gt38?
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Old 02-20-2012, 06:00 AM
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after reading all of that, based on the limited oil flow coming out of several injectors... i would quit jacking around and put a new set of injectors in it. especially if the pistons/walls looked good, valves/seats/guides checked out ok...

to me, it seems farfetched as to why you would pull the heads if you could already see that several injectors were not contributing fully...
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Old 02-20-2012, 07:14 AM

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I agree with the CPS its cheap insurance my truck was missing like crazy failed contibution tests I was about to throw injectors at it until I did some research on here. When and got an IH CPS and it cleared everything up. $30 bucks well spent.
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Old 02-20-2012, 02:58 PM
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Old 02-21-2012, 04:15 AM
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thanks for the replies guys. a new cps is on it's way. i know these trucks have been known for issues with them. and im not just going to throw a whole set of injectors at it now at this point. i did not do the contribution test before doing the heads. a $150 gasket set and a little of my time is one thing, but $1200 of rebuilt inectors is another. much more investigation needs to be done before that happens. is anyone else concerned about the very different idm voltages between cylinder banks?
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Old 02-24-2012, 06:07 PM
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any other input? Im gonna throw in the sensor tomorrow morning and report back, fingers crossed.
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