Hello, I have been monitoring this board for a while and there seems to be a lot of good information floating around. I come to you with a diagnostic question. I have a 1978 Jeep CJ-7 with a 1985 TPI 350 converted to speed density. On my last trip to the mountains, I had an overheat situation (230-250 degees) and had no choice but to keep the motor running due to a seized starter (whole other story!). The motor ran fine despite the high temerature for the better part of 3 hours until we reached the fire road down the mountain. Once I got the Jeep up to speed on the fire road, the motor began to cool down, but as it did, it developed a miss. For the rest of the drive home (2 hours on the freeway), the motor felt (and sounded) like it was running on 6 cylinders. When I got home, I started going through everything I could think of and here is the progress (or lack thereof) I have made:
-148 psi compression is all 8 cylinders
-new spark plugs and distributor (the original external coil distributor was in awful shape)
-new coil
-new CTS/TPS/IACV/O2 sensor
-re-adjusted valve lash
-new EGR valve and solenoid (today)
-new spark plug wires
-fuel pressure holds 42 psi before startup, drops to 38 after startup
-set timing at 8 degrees BTC (with esc unplugged of course)
-no trouble codes
-injectors ohm out at 14.8

I have tried about everything I can think of so I'm hoping someone here can give me an idea of the next logical step to take (and selling the Jeep is not an option ...neither is another motor swap). BTW it sounds like there may be a vacuum leak, but I cannot find it. All the intake bolts are tight.
Anyways, sorry to make my first post here so long, but I'm just trying to give as much info as possible. thanks in advances

Blake

P.s. the motor is run by the 7730 computer.

 

In my 91, I run 6 deg of timing and it has been that way for a long time. Also I have 42 psi fuel pressure when running at around 46 when WOT.

 

Try spraying starting fluid on the bolts where the plenum and runners meet , and runners and intake manifold meet and any other place you think there may be a vacuum leak.(while the car is running) The motor should rev up if you have a vacuum leak

hope this helps

 

Thanks for the input. I'll try that tomorrow. Is there any possibility that a fuel injector is sticking open or closed but still ohming out ok?

 

Sure, but you will never know unless you can take it out for a spray test. That or try reading the spark plugs for a lean or rich condition. Plug reading is not really good as it gives you a rough idea.

 

When I checked the plugs, I found considerable carbon deposits on #2 and moderate fouling on #4 and #6. I was frightened at the amount of fouling on 2, but that may be because of a spark problem...I don't know. I pulled the heads a couple weeks ago and everything was fine. Leakdown was at an acceptable level. Maybe we can brainstorm: what causes a miss?
-spark
-major vacuum leak
-injector problem

I appreciate the help so far.
Thanks
Blake

 

I had a similar problem. Try with a long extension or screwdriver touching the injector body and the other side up to your ear (careful not to short out the injector) , run around to all 8 injectors and see if one injector is not ticking along with engine rpm (dead injector) . I had a stuck injector and it ohmed out just fine.

Good luck

 

After almost a month of avoiding the fuel injectors, I decided to disassemble the fuel rails as a last ditch effort. I found that all of the injectors had become clogged by a fine rust powder (time for a new tank). Several injectors were clogged so badly that I'm surprised the motor actually ran. Anyways, I cleaned all of the injectors out and I can once again burnout with 36 inch tires! Thanks again for the support.
Blake

here's a picture of my baby in case anyone cares:

http://kahuna.sdsu.edu/~darling/imag...icon/ledge.jpg

http://www.jeepcjtech.com/photogallery/Blake1.jpg

 

How did you clean it out? Injectors cannot just be done with a can of spray air. Send it out for a professional job where they balance it and change the pintle and the filter.

 

Where can I have that done? I've been to all of the "competent" speed shops in my area and all they do is sit on their thumbs. Any suggestions?

 

http://www.lingenfelter.com/lingenfe...=17&pf%5Fid=71

When in doubt, call Lingenfelter

 

www.cruzinperformance.com for the injector cleaning. I've never had Rich do my injectors, but I've bought accel parts from him and I was very pleased with the whole transaction. Rich is VERY highly reccomended on thirdgen.org and on the corvette forum.

Anyway... nice jeep. My cousin has a 78 that we've been to hell and back on. We swapped an MPFI 4.0 out of a 91 cherokee in, then he got an 88 4 cylinder jeep cheap. He installed a ford 9" rear with a dana 60 front diff, the 88 4-banger frame, a coil spring 4-link suspension (amazing suspension), and the 78 front clip. Once he gets paint on it, he's going to have an amazing offroad jeep.