No go under hard acceleration

Well.. I need help guys. I'm at a loss here.

1994 4.0L with auto. Just had trans serviced and coolant flushed. After that, it will not move under hard acceleration. Expecially on the freeway (passing, going up hill, etc). I've done cap, rotor, plugs, wire, O2, MAP. While it also seems that the she will not rev over 4K in neutral either. Was hoping it was just a voltage drop somewhere, but at this point, I'm lost and brain fried. I did pull 13 and 14 codes, that was the reason for the MAP replacement. No help there. The only other thing that bugs me is the mechanic that did the service "hosed down the motor" to clean it up. But I can't see this causing a problem with the TPS or IAC, but I could be wrong. And while at low speeds it seems fine... I just have a hard time on the express way. HELP, please.

TIA
Steve

Getting the TPS wet is a sure recipe for a failed TPS. What you describe could well be attributed to a bad TPS. Do a search on how to diagnose a bad TPS.

Could be a dying fuel pump too. That could explain the lack of power at higher speeds/engine loads.

x2 on checking the TPS and fuel pump. Both easy
BSD

Plugged Cat will kill acceleration. I had similar symptoms once, after 40 or so mile on very bumpy roads. After pulling back onto the highway, it was hard to get above 50--certainly impossible to pass anyone! In my case, after the Cat cooled for the night, everything seemed OK until 10 minutes, or so on the road. Then the same thing--no power.

Think I got the problem... going to run her for a short bit while going to the Moto show. When I get back.... IF it's still running good, I'll post my findings.

Thanks !!
Steve

Ok.. so let's start with.. it's not fixed yet. Now.. this all started with me wanting to do maintenance on the ol girl because the thought of new Jeeps make me cringe :gag:

So the big stuff I let my mechanic handle and the smaller stuff I do (most based on time and he has a lift). So I wanted to fix the little things bugging me. Like the lack of heat. I knew that was a plugged heater core, just didn't have the time to do it myself. Had him flush the coolant and while in replace the 2 hard trans lines that have been leaking on my driveway, then do a screen and flush... no big deal right.

After I got it back from him she started shifting strange... didn't really notice it on the way home taking surface streets. But once I got on the freeway, I knew a problem was a foot.

Figured it was from him washing under the hood... maybe bad wires or TPS or some other sensor. So.. let's get to what I've replaced thus far.

1. plugs (champion .035 gap), Bosch wires (lifetime warranty), Accel cap, Mopar rotor.

These didn't help the problem. They seemed to help smooth out the acceleration/idle some.

2. Pulled the codes and was pulling 13/14. Replaced the MAP.. figured.. hell.. I'm in it anyway and did the O2 (only have the one).

These didn't help the problem. Again, seemed to help smooth out the motor a little bit more.

3. This morning... figured damnit... I hate that damn TPS (been through a couple already in it's life with me) and got to Murray's when they opened and got the TPS and Cam Position Sensor (under the cap one).

These did help some, but while on my way to the Motorcycle show (again, on the freeway) she didn't have the passing power. I've also noticed she will NOT shift right unless I "pedal it" or back off the throttle. I do notice that it runs upto about 3K and stays.. will not shift. This seems to be the consistant right now.

NOW... I've called the mechanic (after being up until 2am reading to find that he DIDN'T put Dex III in it, but Mercon V. So.. I'm back to this being a trans problem and not anything mechanical or sensor related. HE IS going to get this back in the morning and flush once more with Dex III as the manual requests, then we'll go from there.

But.. I do have a couple questions still.

1. Not knowing if this is the original trans (bought it with 128K/blown motor... now has 208K) is it possible that the valve solonoids could be showing breakdown?

2. I know that last trans service it had got ATF+3 and didn't have a problem (that was about 20K/2 years ago), but as the debate continues elsewhere, will ATF+3 hurt the trans or is that a comparable substitute?

3. If it's not ANYTHING of the above, WTF is it???? I do know that my CAT is now hollowed out, but the shield still rattles until warm (damn annoying I tell you) but has NEVER shown any signs of causing problems to the driveablity. Muffler is good, that was just done last summer. The ONLY other thing done recently was the ingition switch (on top of the GM column) because it was locked solid from heat. (yes, I fixed the connector problem it had).

I'm at a total lose here. I've read on this wonderful site of damn good info, read the manual front to back, and used logic to figure this out. I'm out of options... short of buying a new Jeep and turning this into a buggy (WAY down the line with a different motor). I really like being without a car payment.. so please.. any suggestions are REALLY welcome.

Thanks
Steve

Hmmm... did I upset people?? Not used to not seeing nothing posted.

But anyway... had the mechanic change the fluid out again. This time using ATF+3 synth blend. This DID correct 99% of the issue. Only thing now is WOT has a bit of a stumble over 3500 RPM before shifting. That to me is acceptable for now... but going to give it a day with the fresh fluid. Then check prices of the valves.

Any other opinions would be helpful.

Steve

TealV6 said:

3. If it's not ANYTHING of the above, WTF is it????

Click to expand...

Check the vacuum line going from the MAP sensor to the throttle body. If it has cracks/leaks, the MAP sensor will give the ECU a reading which does not correspond with current engine load.

I had a similar problem.
The problem is the fuel pump pressure (2psi). The ideal is about 5psi.

DOuble check the numbers on fuel pressure. I believe tehy should be closer to 30 psi without the fuel pressure regulator attached. However, search to be sure.
BSD

Sorry.
My fuel pressure was 2 bar (not psi) and the ideal is about 3,4 bar

I have posted this time and time again... DON'T SERVICE A TRANS OVER 100,000 miles.... It really sounds like the trans is slipping. If It has 208,000 and you changed the tranny fluid its done. Tranny Fluid is very high detergent. It cleans really well if you don't belive me get your hands greasy and put some tranny fluid on them it will remove the grease and grime. Over time and many miles clutch material looses its grip on the clutch plates. Over time the tranny fluid looses its ablity to clean. When you change the fluid after 100,000 miles it usually cleans off the clutch materal off of the plates and thats why it slips. Also the crap that has come off almost always gets in the valve body and makes it stick. I have seen it happen. My bet would be your tranny will get worse and eventualy not move. At that point you need a new tranny. There is no quick fix or magical additive. Its like you trying to add rubber to your tires, won't happen.

Well.. after seeing the last post. I'll throw a few more details that might have been missed somewhere in the translation.

Let's go back to Monday. I did have him remove the Dexron or Mercon V he put in, only problem was, he put in a synth atf+3 now. I am running MUCH better. Only having problem I'm having at this point now is in OD trying to pass at high speeds or up hills. It kicks down, revs to 3K and does not move. If i shift it into 3rd manually, then it goes beyond 3K and pulls. Still not sure why it will not push to redline on a WOT pedal?? Going to read over the AW4 manual I have this weekend and do a few more tests.

As for not servicing over 100K, I've heard that before too. But everything I read is contradiction of the other. I've heard of guys going 300K on the original trans with service being done. (mind you, I DO NOT know if this trans is orig or ever been cracked open). So.. I might drop the synth fluids and find the Dex III stuff and try that with some other voodoo.

I'm still open to any suggestions. And I will be looking at fuel pressure too!

Steve

Ok.. haven't had much time (thanks to job) to get some testing done. But I have been trying to pay attention to shift points, where/when i'm having issues.

I'm starting to think at this point some of this might be motor related.

I say that because just in general, it will not go above 3K rpms. Even in neutral (just trying a theory) it would bog out at 3K and then run like crap for a few moments afterwards. While doing all the other things trying to run this problem down. I still have yet to replace the coil (will try to find time this weekend) but if anyone can confirm that the distributor shaft has 1-2mm of movement with the rotor off of it....

This and the coil are a friends thoughts.. but I just have a hard time seeing even 2mm of play causing this much issue. It seems to be more of a "ignition dropping" problem at 3k... like something is just not able to handle the signal fast enough compared to low speeds.

Any thoughts??