I had nearly identical problems. I went over a year though before I spotted my grounding injector wires. The slit on the bottom of that black ribbed deal let a few wires out on the bottom. Nice that it will really go when you floor it eh? Once mine backfired out the intake and blew a mouse nest out the front grille. Drove through the confetti. RIP mouse

That tin shield would expand with heat and sometimes ground a few wires a little. Whatever your setup, those wires from the injectors to the PCU can do that if they ground.

(retyped after having my text just vanish)

 

Check your harness for chafing as Flintstone describes.

At idle, wiggle the harness along the valve cover and over under the MAP sensor. See if the idle changes.

There's a possibility that your sensor ground circuit in the harness is faulty also. That won't necessarily show up in the wiggle test but can be tested in about 20 seconds with a cheap meter.

Have you ever refreshed your grounds at the engine dipstick tube stud? Very critical to do so as the ECU itself and other very important sensors ground there.

And you're correct, Renix does not store codes.

 

Just wanted to jump in in this, mines an 89 original renix with 270k, and has the same problem. She runs good at highway speed but just off idle and in traffic its horrible. I will be watching this thread closely...

Also, one thing I didn't see mentioned here was the fuel pressure regulator, its a pretty cheap part and could cause the higher rpm problems, and probably right off idle too. Didn't work on mine tho lol...

 

If fuel pressure is suspected, check it to verify.
TPS can be adjusted and tested.
Grounds are a mandatory starting point. Period.

 

I have read several thread, and i have seen you mention this in several threads. So I did, I checked out everything, all looked good. one wire looked like the wire my have been broken so i spliced it. Put thick electrical tape on spots the might have a rubbing problem later on down the road. Poor mouse, I bet that was a sight to see.

Yes any ground I could find, really gave the block ground a good cleaning. Also the one on the drives side apron. cleaned the paint off and put a new bolt in. The strap from the firewall to the intake.

Thank you for all your suggestion, I have tried alot of things. Sorry I forgot to put alot of this in the first post. Tomorrow I am going double check alot of this. Thanks every one again. I wish this problem was something simple and quick to fix.

 

Another thing I have been thinking about, but I dont know for sure, does the renix have transmission control module. The box under the glove box. Does that control the engine at all?? or just the transmission?? I can put it into park or neutral, and with the gas pedal steady at 2000 rpms it runs fine. No miss, no hesitation, nothing, purrs like a kitten. ONLY DRIVING and the RPM's are at a steady 1800-22000 RPM's is when I get the hesitation. Any thoughts??

 

YEa! You busted me. After all that chugging and bucking for over a year (now and then), I really want to try to share that. A wire hiding under my nose and all this brainy stuff to suspect. Interesting that it will still blast off like a rocket when floored. Maybe the signal to the injector is strong enough then to over whelm the wiring fault there. Maybe Crusier or somebody less clueless than myself can comment on that.
Also, I'm pretty sure Crusier meant to be double sure the ground from the back of the valve cover to the fire-wall is clean and fresh, and to consider ADDING a ground from the dip-stick tube mount bolt to the stud below the shock mount. I added mine from a small bolt on the AC compressor to a rad bracket bolt. Not as neat, but a 2'nd ground anyway.( Oh, I see now you covered Grounds)

My 90 does have a transmission control module.,,,,no clue,,,

Boy Bigz, sure sounds like mine. Ever put the right edge of your right foot against the carpet to hold the pedal "just there", below bucking but still throttling some?

Just re-read your thread. Really have to suspect wiring. I know nothing about checking injector voltage/signal except it would be a ***** for an intermittent problem that pops up at speed. Short of a dinomoniterer I wonder if a guy couldn't run a jumper from an injector into the cab and watch voltage while it's F#%*ing up?

 

Well it finally stopped running. Had to tow it home. I know its getting fuel to the rail but that's all I know. A big storm came through so didn't get to start figuring it out. I hope this is related to the hesitation and all problems fixed at once. Keep my figures crossed. I does turn over and start for a split second. Then dies. I will check for fire and check the fuel pressure tomorrow.

 

you can get the codes (if you want to call them that) there is a diagnostic port under the hood. chrysler shops usually have the old machine that plugs in to it, and can figure it out. Maybe somebody on this forum may have the machine.

 

Not that I have any reason to think it's likely, but that test Cruiser came up with for your new cps sounds pretty easy. I haven't done it but it looks like just a few minutes. Mine only did a complete no-start while I was dating an unusually attractive blonde, Tracy. As soon as she left it started right up.

 

I have the DRB-II and it pretty much gives you some tests to do but it's best at reading live data. No codes are stored!!!

 

I am HIGHLY suspect of the new CPS's output. Seen it too many times. Why skip a 20 second test? Only one way to know.

And yes, I advocate putting an additional ground cable from the dipstick tube stud directl to the stud on the inner fender. What better place to attach it on the block than the stud that holds the most critical grounds?

 

After a very long day, a couple of friends and I got it running again. We went to swap a coil ,out of my friends jeep, and put it in mine. That's when he saw a spark from the ratchet to a wire. One of the wires going to a silver box that mounts to the relay bracket was burned in half. It also had a fuseable link. So we rewired it with a new fuse and she started up. I don't know if that was actually the problem or if we knocked the coil to working order again. Time will tell

BUT IT DID NOT FIX THE HESITATION PROBLEM!!!! Today we checked the fuel pump, changed the fuel filter and ran new rubber hose from fuel pump to metal lines. Checked the CPS, injectors and moved to the coil and that's when we got it running and called it a day. So now back to guessing on what this hesitation problem is.

 

Do a compression check. If one cylinder cannot perform, the results will be less evident at higher RPMs. Compression tests are a quick and easy thing to do and can save you TONS of time and money later. Each cylinder should be within 10% of the others (i.e. they won't match each other exactly)

Compression testers are about $20 at your local parts store. Be sure to get one with multi-sizes of nozzles included.

Remember: You need fuel, spark, air----and compression in each cylinder, all at the right 'time'.

 

I'm still stuck on your problem being a wire, solely based on that it was on mine! I think the injector wires run to the PCM. I found this below in another post,;

A friend of mine, and an excellent tech, did this to fix an intermittent problem on his 88. He removed the ECU., unplugged it, sprayed the connectors on the ECU and on the Harness with a good electrical contact cleaner. Before putting it back together, he used a small pick to tighten up the female connectors that grab the pins. Never had the problem again.

That now reminds me of something I like to do on any newly acquired Jeep. I take about 20 minutes and go through the engine bay unplugging connectors and relays, inspecting the terminals, spraying out the connections with a good elictrical contact cleaner, applying a bit of dielectric grease, and putting them back together. Everyone you can find!!


I see now/again you changed the PCU. With a new one? With pretty new connectors?
Does anyone know is there an over-ride, or circuit, that fires the injectors, goes flat out when you floor it? The carb. equivalent of secondaries.