co-MAN-che

I purchased a 4wd comanche a month ago, and I knew it was going to need repairs done, I had no problem with it. But since then, I've run into a problem that I have done everything within my mechanical knowledge boundaries to fix, yet I can't correct the issue. The truck will idle all day just fine, and if in park or neutral, you can bring it all the way to rev limiter, put it in gear and it will idle fine as well, but give it gas and it will hesitate and stumble so bad it can't even move forward (reverse is O.K., but just ok). I have replaced EVERY. SINGLE. SENSOR on this thing and cannot seem to fix it. I replaced my fuel pressure regulator, distributor, coil, cap, plugs, wires, and stator pickup wire as well. The only thing I can think of left is the ECU itself went bad, but before I spend 125+ dollars on that I would like some confirmation from fellow jeepers.

ZJMAX

Check wire continuity from each sensor all the way to the ECU. Check all your grounds. Check the sensors to make sure they are all within specs (new parts don't always work properly).

Max

1arunem

TPS comes to mind. Would check the new one.

Bustedback

Check the fuel pressure and for exhaust restrictions before throwing any more parts at it.

co-MAN-che

ZJMAX: can do boss

1arunem: How do I go about testing the sensor itself?

Bustedback: Exhaust is free of restrictions, but my same thread under comanche tech said check my fuel pump because it can properly feed an idling truck, yet put under load it chokes because the pump itself fails under certain current loads, I happen to have a brand new fuel pump so I'll go ahead and replace it

cruiser54

Whoa big fella!!!

Click on the pink link in my signature and do Tips 1 through 5 before spending another nickel.

1arunem

Do Cruiser's suggestions first.

Check TPS with a meter to make sure it is within spec throughout the range.

co-MAN-che

I am in the process of performing cruiser's tips, but I tested the tps per 1arunem's suggestion and found pitifully low voltage coming from my tps signal output wire. If I'm not mistaken I should have between .4 and .9 DC volts idling and between 3.5 and 4.5 DC volts when wide open throttle. with the key on, engine off, I am reading 0.02 volts idling position and 0.12 volts wide open. Figured this is my problem and am tracing this wire down while cleaning and refreshing connections and grounds

DFlintstone

Since it works in reverse I'd check the engine to tranny bolts. (seriously) Also I suppose that could be an engine ground issue.

As far as the TPS voltage...make sure you read the process correctly, and you have your meter set on DC Volts. On most meters that would be using the 20 Volt scale.

ehall

My bet is on fuel pump

cruiser54

Here's how to test a TPS.


RENIX TPS ADJUSTMENT

Before attempting to adjust your TPS, there are two things that need to be done.

1) Be sure the throttle body has been recently cleaned. It's especially important that the edges of the throttle butterfly are free of any carbon build-up.

2) With the Key OFF, and using the positive (red) lead of your ohmmeter, set on the lowest scale, probe the B terminal of the flat 3 wire connector of the TPS. The letters are embossed on the connector itself. Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it parallels the valve cover and also over near the MAP sensor on the firewall. If you see more than 1 ohm of resistance, or fluctuation in your ohms reading, some modifications to the sensor ground harness will be necessary. The harness repair must be performed before proceeding. I can provide an instruction sheet for that if needed.

TPS ADJUSTMENT FOR ENGINE ISSUES

Both RENIX manual and automatic transmission equipped XJs and MJs have a flat three-wire connector to the TPS which provides data input to the ECU. The three wires in the connector are clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. DO NOT UNPLUG THE CONNECTORS !! Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors. Note the voltage reading--this is your REFERENCE voltage. Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For example: 4.82 volts X .17=.82 volts. Loosen both T-20 Torx screws attaching the TPS to the throttle body and rotate the TPS until you
have achieved your desired output voltage. Tighten the screws carefully while watching to see that your output voltage remains where it is supposed to be. If you can't achieve the correct output voltage, replace the TPS and start over.

Sometimes, after adjusting your TPS the way outlined above, you may experience a high idle upon starting. If that happens, shut the engine off and reconnect your probes to B and C. Start the engine and while watching your meter, turn the TPS clockwise until the idle drops to normal and then rotate it back counterclockwise to your desired output voltage.

TPS ADJUSTMENT FOR AUTOMATIC TRANSMISSION ISSUES

RENIX automatic transmission equipped XJs and MJs have a TPS with two connectors. There is a flat three-wire connector, same as the manual transmission vehicles have, and it is tested the same as outlined above—FOR ALL ENGINE MANAGEMENT RELATED ISSUES.

However, the automatic TPS also has a square four-wire connector, clearly embossed with the letters A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module. THIS SQUARE FOUR WIRE CONNECTOR IS USED FOR TRANSMISSION/SHIFTING RELATED ISSUES ONLY. First off, DO NOT UNPLUG THE CONNECTORS !! Key ON, measure voltage between "A" positive and "D" ground by back-probing the connector. Note the voltage. This is your REFERENCE voltage. Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage. For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage. If you can't, replace the TPS and start over. So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and the other side feeds the TCU.

For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced. The square 4 wire connector is just not used.
Revised 12-15-2013

co-MAN-che

Cruiser: My throttle body is clean, for it is new. I tested the resistance of the signal wire (lowest setting on my meter is 200) and got 00.3 ohms. When I wiggled the wires, and I wiggled the $#!t out of the harness in multiple locations and got no fluctuation. I have an HO model rather than a RENIX, so my TPS isn't adjustable

co-MAN-che

I have repaired my grounds and checked for excessive resistance in my wiring between my TPS. I am still feeling it is my ECU because of no change in vehicles performance.

DFlintstone

So Cruiser is wasting his time because you didn't fill out your info. Isn't that special. HO has a PCM, not an ECU Btw. Best of luck....

CCKen

Change the "ECU".