It sounds like the distributor is a tooth ahead? But I thought the cps was responsible for ignition sequence?

 

Had not given much thought to distributor not being in sync with crankshaft, but your suggestion is worth pursuing. I'm going to investigate. I'm also going to take a much closer look at the condition and installation of the crank sensor Thanks!

 

Go to jeepslimited.com, create an account, and then you can download the FSM.

Ignition timing is based off the crank sensor input to the PCM.

It should run without detonation on 87 octane, so something is up.

 

Thank you for responding. My apologies for the slow response. Been offgrid.

I really appreciate the steer to the FSM. Lets see what the factory says. Will report back when I have something worth saying.

 

What does “.25” mean?
.25 is the solution to 17:68

 

I'd kinda like to know what year the jeep is, what engine it has, as well as a picture of the rotor with the distributor cap off, with the engine at TDC Compression stroke.

 

So, have you removed the distributor or the timing chain? Did you inherit it this way? Or did something change?

I had an arduous journey with timing on my 4.0L recently…very arduous.

 

I am intrigued by your comment "arduous journey with timing. . ." Care to share the story?

 

This is a 94 or 95 4.0L, correct? If so, where are you getting a base timing spec of 9.5* from? The timing is not adjustable, therefore there should be no spec and I cannot find one.

In the real world, and lets use a 4.2L carb engine in a Jeep. You set base timing to about 8 or 9* and then you plug the vacuum advance back in like it is supposed to be and it is now 20 some degrees at idle. When you give it gas the intake vacuum lowers and the timing drops off.

Fuel injection runs the same basic way. It has more advance at idle and when you give it gas the MAP detects the lower intake vacuum and drops out some of the timing.

Does the check engine light work? Do you see it when you turn the key on? If yes, is it on while driving? If yes, have you checked the codes. If the check engine light does not work, it needs to work. Any codes need to be noted.

If it has good power and pinging going up hill it could be carbon build up in the combustion chambers, a bad O2 sensor that is shifted and causing it to run lean, or a MAP sensor.

 

Thank all you folks who took the time to post and offer up suggestions.

Big shout out to JKP for steering me to a site that allowed me to download a mostly complete '95 Chrysler Jeep FSM. This is the piece of the puzzle I was missing. Mucho gracias my man.

The vehicle in question is a 1985 CJ7 4.2L with a dealer installed Mopar Performance kit #P5249610, necessitated by its move from TX to CA, circa 1997. See the attached photo of a prominent decal required by C.A.R.B. (California Air Resources Board) for exemption from smog testing in the state. A summary of this kit is to replace the original carburetor with MPFI and computerize all engine control functions and emission accessories so as to meet the requirements of California smog legislation. That the vehicle runs better, produces more power, gets better fuel economy and is generally more reliable is a happy bonus. The instructions for this kit specifically states THE TUNE UP PROCEDURES AND ENGINE SERVICE ARE THE SAME AS A 1994/1995 4.0 LITER JEEP WRANGLER. Thus my reaching out to this forum for some help finding the necessary FSM.

The vehicle recently came to me as is, with a reputation for dealership and concierge quality maintenance and repairs. There is no reported recent major repairs or mechanical "customizing," and I have not found any evidence to the contrary. As noted in my original post, it runs flawlessly except for the severe pinging under light to moderate loading.

In an earlier post I reported a 9 degree BTDC timing specification at idle. That was wrong. As Boojo35 correctly pointed out, there is no manually adjusting the ignition timing. Install the distributor per specification and let the computer do all the work.

The kit included a new wiring harness, but no MIL plumbed into the dashboard. I assume there must be a OBD1 or 2 port somewhere, I just haven't got that far yet. But its on my list.

Attached are photos of the distributor in its undisturbed state and after I removed and re-installed it. Note that yes, I did re-install with the indexing lock pin. And also note the re-installed configuration wasn't much different than the undisturbed state. Cold starts still easy and runs as well as before. Still getting the same severity of ping under load. Advanced timing at idle was modestly lower (16+/- degrees) and at no load 2000rpm it was off the scale to somewhere around 30+/- degrees. The delta of 14 degrees between the two is a defensible number for an unmodified 8+/- : 1 compression ratio factory engine on 92 octane, so I'm thinking the PCM is not failing in that portion of its firmware.


Investigating the O2 sensor and MAP are good suggestions. Gotta find the OBD first to cut down on the guess work. Then I want to look into it.

Louie 4: "an arduous journey with timing" sounds intriguing. Do tell.

Again, thanks all for the assistance. I value your input.

Jim

 

you can adjust the timing a couple degrees each way with a drb 2 scan tool, but good luck finding one

 

FIND A REAL SHOP
SAY FIX IT.
You did it all wrong.

 

AGAIN

 

YOU DID IT WRONG

 

YOU DID IT WRONG

 

YOU DID IT WRONG

 

Well, that was quite helpful. Thanks for responding to my post.

 

@Boojo35 I apologize for the long post jokes. The end.

 

I apologize for the long post jokes. The end.

Its all good. My wife tells me that I like the sound of my own voice.

 

A quick note for you about the check engine light, there is a link on the Hesco website with the MPI instructions, Step 29 talks about the check engine light. Sorry first post so cant attach links.

 

Have you tried reaching out to local dealerships or looking into online databases that specialize in such things? Sometimes, automotive schools and libraries have resources that could help you as well.

 

Maarklarius: thank you for responding and the suggestions.

Update: I have gathered up a number of factory tech documents that have allowed me to more fully understand what the ECM is designed to do (and also not expected to do), how it does it, and performance specifications for the various sensors and devices that constitute the system.

Upon a better understanding of the system and closer inspection of the vehicle, there is indeed a Check Engine Lamp (CEL) mounted in the dash. Further, it is functional. It does not illuminate when driving. The only DTC(s) via the CEL is 12 and 55. I have disconnected the battery a number of times for other reasons in the recent past which explains the 12. In this instance DTC 55 signifies the end of the DTC file within the PCM. I am currently driving the vehicle to get past the magic 50 ignition cycles required to fully populate the internal file with any DTCs to be certain I did not erase data when disconnecting the battery power. I have also located the OBD1 socket.

While I have not ruled out incorrect timing between the crank and cam gears, I want to eliminate other 'lower hanging fruit' before pursuing this.