letinsh

87 wagoneer limited
201k miles
Aw4
In the last 3k miles:
New plugs, cap, rotor, plug wires, refreshed grounds, 4 hole injectors, and just got done doing fuel pump. Fuel filter has been replaced, but I don't have specifics...with in the last year.

At idle, there's never a problem. At speed or when pulling away, there is an occassional hesitation/false start that used to happen then pass, but has started taking longer for the motor to "bounce back". Letting off the pedal helps, gassing it does not. Going over bumps, it has several times just died -no sputter, gasp, etc. Just quit. It's not an electrical issue, as the radio, lights, etc never die. Just the motor. I was thinking it was the pump, but clearly that didn't solve the issue. (I have good, solid fuel pressure at the rail)
It's not cool trying to make a left turn or cross an intersection wondering if the heep will quit on you....

Any suggestions on what next to try?

hankthetank

What brand of fuel pump?

letinsh

Put in an entire airtex sending unit with pump, without reading the reviews on here, but it leaked like a seive (lost 10 gal between 2 fillups trying both included seals) and was loud as *****, so I pulled it, installed a Bosch pump (69302).

cruiser54

Test your TPS next.

RENIX TPS ADJUSTMENT
Before attempting to adjust your TPS 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.
IMPORTANT NOTE: Using the positive (red) lead of your ohmmeter, 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.
MANUAL TRANSMISSION:
RENIX manual transmission equipped XJs have a three-wire TPS mounted on the throttle body. This manual transmission vehicle TPS provides data input to the ECU. The manual transmission TPS has three wires in the connector and they're clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. 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. Adjust the TPS until you
have achieved this percentage. If you can't achieve the correct output voltage replace the TPS and start over.
AUTOMATIC TRANSMISSION: RENIX automatic transmission equipped XJs 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 the manual transmission equipped vehicles—FOR 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. Key ON, measure voltage between "A" positive and "D" ground. 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 AUTOMATIC TRANSMISSION RELATED ISSUES. Check the four-wire connector side of the TPS.
If you have ENGINE issues check the three-wire connector side of the TPS. 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.
Revised 05-20-2012

cruiser54

And since it's an 87, do this:
Renix Jeep C101 Connector Refreshing
　
The C101 connector on 1987 and 1988 Renix Jeeps was a source of electrical resistance when the vehicles were new. So much so that the factory eliminated this connector in the 1989 and 1990 models. The factory recommended cleaning this connector to insure the proper voltage and ground signals between the ECU and the fuel injection sensors. We can only imagine how this connector has become a larger source of voltage loss and increased resistance over a period of almost 25 years. The C101 connector needs to be cleaned at least once in the lifetime of your vehicle. Chances are it’s never been done before.

Almost every critical signal between the engine sensors, injectors, and the ECU travel the path through the C101.
The C101 is located on the driver’s side firewall above and behind the brake booster. It is held together with a single bolt in it’s center. To get the connectors apart, simply remove the bolt and pull the halves apart. You will find the connector is packed with a black tar like substance which has hardened over time.
Take a pocket screwdriver or the like and scrape out all the tar crap you can. Follow up by spraying out both connector halves with brake cleaner and then swabbing out the remainder of the tar. Repeat this procedure until the tar is totally removed. This may require 3 or more repetitions. Wipe out the connectors after spraying with a soft cloth.
If you have a small pick or dental tool tweak the female connectors on the one side so they grab the pins on the opposite side a bit tighter. Apply a true dielectric grease, not the stuff that came with your brake pads, to the connection and bolt it back together.
　
　
Revised 11-29-2011

letinsh

Right on - I appreciate the guidance. I cleaned the TB really well when I did my injectors.
For the above proceedure, is it performed Key ON as the other 2 TPS tests or does it not matter? It also seems to say to unplug the connector and probe the harness side. That makes sense to me as we're checking that harness ground, but wanted to verify before making a fool of myself.
Since we're on the subject, if you could post that harness repair proceedure you just mentioned, that'd be great -then it'll be on hand when I need it

DFlintstone

Yes, have it on, yes like you say, the "Jeep side" to check the ground. I suppose he was talking about the "Ground Refreshing" he wrote. It's in the link in my signature...Cruiser really knows those Renix! Your CPS signal goes through that C-101, so even if it tests good it still has to get through there.

mud'njeep

Try putting in a new crank sensor. i had problems like this and it turned out to be a simple fix. i replaced alot of the same things you did and turned out i didn't need to.

cruiser54

Key on to test the TPS. Key off to test the sensor ground circuit.

cruiser54

The OP is testing his way to a solution and not throwing parts at his Jeep. That way he won't have to throw any parts at it hopefully, as it may be a wiring harness connection issue.

DFlintstone

X2, I wouldn't be hasty to spend that $50. On these Renix Jeeps you can test that CPS in the time it takes to tie your shoes!

letinsh

Now the trick is finding the time to do the checks...
Thanks for the suggestions. When I get data, I'll post it.

For what it's worth, these last few days haven't been nearly as bad as it was pre-pump swap.

letinsh

Woot for the scientific process! Cruiser, you are an invaluable resource. Did the resistance to ground check on the TPS and everything looked fine (.2ohm) until I touched my grubby paw to that c101 connector. That needle on my multimeter started swinging left and right faster than a politition in an election year. Next step is to carve out some time to perform the cleaning proceedure...I seem to remember reading about a c101 bypass/removal proceedure somewhere....

cruiser54

The cleaning may very well fix it. Tweak the pins, too. Check it afterwards.

If it's not better, bypass it with the sensor ground. I've got a hokey write-up with an even hokier diagram if you wanna use it. It also addresses the poor crimps in the harness for all the other sensors. More I think about it, that may be the best thing to do, along with cleaning the C101 because of all the other signals that go through it.

letinsh

Ok, a few weeks back I cleaned out my c101....what a mess.

Yesterday, I was able to chase that ground issue with the TPS. B terminal to bat. neg. was varying anywhere btwn 8 and 300ohms, depending on where I wiggled. Pulled everything apart, found the engine side brown/white splice and cleaned it via brass brush and electronics cleaner (no soldering iron). Taped everything up again, and now I'm at 1.8ohms +-2-3ohms as I wiggle the c101 (good enough for me - I'll chase that issue another day).

Now to test the TPS:
My reference was 4.95VDC X .17 = .84VDC for the proper output voltage.
My output voltage was .54VDC, so I adjusted it up to be in-spec.

Let's see if this helps my hesitation issues...
Will report back as I get more data.