Idles great - wont take throttle

I am at my wits end on this and am trying once more to get some clue as to what is causing my problem. All of what I have done has made absolutely no difference.

I had posted about this a couple weeks ago, got some suggestions. All have been checked and implemented to no avail.

I thought I would start another new thread so that anyone who might have some advice doesn't have to wade through the other posts.

Vehicle:
1989 Cherokee 4x4
4.0 litre
RENIX computer control system
232,568 miles

Symptoms:
- Engine stalled at a traffic light. Wouldn't restart (cranked but no fire)
- Towed across the street and there I installed a new Crank Position Sensor
- Engine then started as it should, idles great but would not take any throttle without breaking up and backfiring badly.
- Seems to be a timing/spark/timing advance type issue. Also seems to be very rich mixture problem as the exhaust smells very rich.

Whats been done/checked/replaced:
- New Crank Position sensor (as mentioned above, not another one since)
- New spark plugs
- Checked fuel pressure (32psi with regulator vacuum, 39psi without vacuum)
- Fuel pressure readings are at idle as the RPM's will not go above 1200rpm
- Replaced MAP sensor
- Replaced TPS
- Replaced ignition control module and coil
- Replaced O2 sensor (used one out of known running engine)
- Checked and found no vacuum leaks anywhere
- EGR has been removed from this engine two years ago. Not the problem.
- Catalytic converter was removed one year ago. Not the problem.
- Timing chain replaced two years ago.

cap, rotor and have you checked the bolt that holds the tab on the dost .

I do want to add that I did the three following things and these are the results:

- Unplugged MAP sensor connector. Engine immediately died.

- Unplugged MAP vacuum line. Engine RPM's went down to lower than normal idle speed.

- Moved the TPS wiper arm while at idle. Engine sputtered a bit but did not do much else.

PolishX said:

cap, rotor and have you checked the bolt that holds the tab on the dost .

Click to expand...

Cap and rotor are not that old and are high quality NAPA gold series. The inside of the cap and rotor button dont look new but are not that bad.

Distributor tab is present and is tight.

still might check for a crack it is plastic . may be worth the time to pull dist and see if that gear at the bottom is tight or gnawed up ,is an 89 OBD 1?

Yes, it is OBD1

I am just stupified that it can run perfectly one moment, stall, and then run like absolute hell 30 minutes later.

The only things I have not done is replace the cap rotor, distributor itself and the ECU.

is it throwing codes ? do you have a code reader ?

Tally_XJ said:

Yes, it is OBD1

I am just stupified that it can run perfectly one moment, stall, and then run like absolute hell 30 minutes later.

The only things I have not done is replace the cap rotor, distributor itself and the ECU.

Click to expand...

A few things pop into mind, do an ohm test on your CPS, when the motor is hot. Do a resistance test on the CPS wires, you will have to unplug the CPU and will need a good diagram.
Check the reference (input) voltage to your MAP. What is the voltage in and out for your TPS?
Remove the vacuum line for the MAP, plug one end with your finger and blow, check for leaks. Blow into the hole in the side of the TB, where the MAP ülugs in, see if it is plugged or restricted. Make sure you don't reinstall the vacuum line into the blind hole in the side of the TB, there are two possiblilties.
I'd do an ohm test on most every sensor wire. And check the harness where it runs down the front fo the motor and underneath to the engine temp. sensor, the O2 sensor and the knock sensor. The front harness has been known to cook onthe manifold and cause shorts. Some of the sensors share a common power supply, if there is a short to ground someplace, the values are gonna be screwed.
Alldata has most of the sensor tests listed and also has a breakdown of the wiring in sub sections. Alldata is a bit easier to understand than the FSM on occasion.
I most always check the connectors and harness first, before replacing any sensors. Everything from your injectors to your CPU and TCU ground at the dipstick holder. Excessive resisitance in the ground circuits, will cause you grief.

check that the distributor is not loose. Problems with the distributor gear would make the motor act like it wasn't indexed properly, and would lead to off idle problems, much as a timing chain one tooth off would.

PolishX said:

is it throwing codes ? do you have a code reader ?

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I am not sure how to get the codes. I dont have a reader for OBD1. There is no check engine light on anywhere on the dash but I am not sure it even has one.

8Mud said:

A few things pop into mind, do an ohm test on your CPS, when the motor is hot. Do a resistance test on the CPS wires, you will have to unplug the CPU and will need a good diagram.
Check the reference (input) voltage to your MAP. What is the voltage in and out for your TPS?
Remove the vacuum line for the MAP, plug one end with your finger and blow, check for leaks. Blow into the hole in the side of the TB, where the MAP ülugs in, see if it is plugged or restricted. Make sure you don't reinstall the vacuum line into the blind hole in the side of the TB, there are two possiblilties.
I'd do an ohm test on most every sensor wire. And check the harness where it runs down the front fo the motor and underneath to the engine temp. sensor, the O2 sensor and the knock sensor. The front harness has been known to cook onthe manifold and cause shorts. Some of the sensors share a common power supply, if there is a short to ground someplace, the values are gonna be screwed.
Alldata has most of the sensor tests listed and also has a breakdown of the wiring in sub sections. Alldata is a bit easier to understand than the FSM on occasion.
I most always check the connectors and harness first, before replacing any sensors. Everything from your injectors to your CPU and TCU ground at the dipstick holder. Excessive resisitance in the ground circuits, will cause you grief.

Click to expand...

I didnt list it in this post, but I did in the one I mentioned before.
I have already checked the voltage at the MAP and TPS. All were good. CPS ohm's are good.

Tally_XJ said:

Yes, it is OBD1

I am just stupified that it can run perfectly one moment, stall, and then run like absolute hell 30 minutes later.

The only things I have not done is replace the cap rotor, distributor itself and the ECU.

Click to expand...

The only thing you haven't done is systematically test the sensors and then the harness. Then basic power supply voltage to the componenets and check other basic automotive stuff.
You said the EGR has been plugged? How so?
CPS is heat senstive, sometimes the motor won't start at all when the CPS is going bad. Sometimes they will not start, start hard and if they do start will run like absolute crap, when the CPS is hot and near the outside of it's resistance envelope. The CPS values change with resistance, you really have to figure the resistance at the CPU plug, you may be picking up excess resisitance in the harness or a connector someplace, which is causing the CPS signal to get flacky.
No spark is often the CPS *circuit* (circuit means the CPS and associated wiring). Fuel problems at idle (way to rich) are often the MAP, MAP circuit or MAP vacuum. If the vacuum is plugged (or leaks) to the MAP or is really restricted, it can cause grief.
I've rarley heard, buying and installing componenets as being an efficient way to troubleshoot a system. It's called getting lucky and actually doesn't happen often.
For every sensor I've ever replaced, I've found 3 or 4 connector, ground or harness problems.
I'm getting frustrated just reading your post I'll have to read back through a little more carefully. Have you checked the cam position sensor for input voltage, pulse and shorts?

8Mud said:

The only thing you haven't done is systematically test the sensors and then the harness. Then basic power supply voltage to the componenets and check other basic automotive stuff.
You said the EGR has been plugged? How so?
CPS is heat senstive, sometimes the motor won't start at all when the CPS is going bad. Sometimes they will not start, start hard and if they do start will run like absolute crap, when the CPS is hot and near the outside of it's resistance envelope. The CPS values change with resistance, you really have to figure the resistance at the CPU plug, you may be picking up excess resisitance in the harness or a connector someplace, which is causing the CPS signal to get flacky.
No spark is often the CPS *circuit* (circuit means the CPS and associated wiring). Fuel problems at idle (way to rich) are often the MAP, MAP circuit or MAP vacuum. If the vacuum is plugged (or leaks) to the MAP or is really restricted, it can cause grief.
I've rarley heard, buying and installing componenets as being an efficient way to troubleshoot a system. It's called getting lucky and actually doesn't happen often.
For every sensor I've ever replaced, I've found 3 or 4 connector, ground or harness problems.
I'm getting frustrated just reading your post I'll have to read back through a little more carefully. Have you checked the cam position sensor for input voltage, pulse and shorts?

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Sorry my post frustrates you 8Mud. All of those parts that I "threw" at it didnt cost me a dime. I have availability to many parts donor Cherokees that are known/currently running Jeeps. The CPS is the only new part I purchased.

My model year didnt have a Cam Position Sensor. That started when Renix ended. Mine does have a hall effects type pickup in the distributor, but I just dont think that is the problem. It idles just too well.

I am thinking it is actually a bad (out of the box) Crank Position Sensor. Of all the sensor diagnostics I did, the CPS readings were the only ones that were "on the fringe".

Wow I was just getting ready to post this same exact issue with my 90 XJ 4.0L, A.T., 231 and came across this thread. Mine is doing the same exact thing. It idles fine, rev UP TO 1200RPM and anything after that it just pops and can smell fuel. I was out on a trail ride after 3 hours of continous running we got about 1mile from my house at the end of the trail, took it out of 4wd, moved about 5ft when it backfired and shot out a big puff of black smoke. I haven't had much of a chance to work it, but I did try a few things while off from work last Friday.

Less than 200 miles on new NAPA cap, rotor, wires, coil, and new plugs

Extra KNOWN good parts used to troubleshoot:

spare TPS
spare cap & rotor
spare coil
no vaccum leaks that I could find

Hopefully one of us will figure it out and be able to get our Heeps up and going

Almost forgot about this. I also tried another MAP sensor that was good from a running Heep and no difference

Yeah, your problem does sound just like mine. I am going to try another new Crank Position Sensor since it has a one year warranty and I am in pretty good with the part store I purchased from.

How is this thing a OBDI if its a 89', have you swapped out the RENIX controls, ecm etc?

I would check and make sure that the distributer is set at #1 terminal when #1 cylinder is at TDC COMPRESSION stroke. I had similar problems recently with my 90' missing/stumbling at off idle cold. It turned out to be my new harmonic balancer's timming mark was not at TDC when the piston was. It had me off by a full tooth on the timming. I will never trust another timming mark on a HB again!.

I'm not saying this is your problem, you may have some distrubuter isues, or a timming chain issue, but if you check the indexing it can either eliminate or show a problem.

Jon

have you checked/replace the IAC???

xjtrailrider said:

How is this thing a OBDI if its a 89', have you swapped out the RENIX controls, ecm etc?

I would check and make sure that the distributer is set at #1 terminal when #1 cylinder is at TDC COMPRESSION stroke. I had similar problems recently with my 90' missing/stumbling at off idle cold. It turned out to be my new harmonic balancer's timming mark was not at TDC when the piston was. It had me off by a full tooth on the timming. I will never trust another timming mark on a HB again!.

I'm not saying this is your problem, you may have some distrubuter isues, or a timming chain issue, but if you check the indexing it can either eliminate or show a problem.

Jon

Click to expand...

I guess its not OBD1 then cuz its full Renix unfortunately.

However, I do know, from searching many times, that on Renix engines, the crank pulley TDC mark should NOT be at "0" when the distributor rotor is pointing at #1. My timing is set correctly, its not a distributor out of time issue.

RNMedic said:

have you checked/replace the IAC???

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Yes, I did. However, IAC motor has nothing to do with the engine after the throttle is opened. It only controls the amount of air that is allowed to bypass the throttle plate flap when the throttle is closed.