Windsor 90 Laredo

I have a '90 Laredo automatic 4.0 L6. I have new air filter, fuel filter, o2 sensor, spark plugs & wires. I have cleaned the grounds (all I can find), the t.b. and all the electrical connectors. The IAC looked new when I cleaned the T.B. I plan to install a new crank sensor, and cap and rotor.
My issue is the engine (cold or warm) surges at idle. It can jump from 0-1000 rpm and sometimes will stall out. It has stalled while driving in the past when it was also temporarily running high rpm or low rpm. The weird thing is how the severity of the surge will change. It's always their at idle, but being in gear with the transmission can make it way more intense. I know it could be a lot of things. Can't find any vacc leaks. Egr seems ok, anyone have an idea with the transmission changing the effect? While troubleshooting I noticed if I pull the front vacc line off the egr solenoid switch (which is a used part) the idle seems a little better, and once I reattach it the jeep dies. If I plug it there's no difference than letting it openly suck air. The surge in idle is constant, except when accelerating, but the severity of it changes. Once the engine is warm and I come to a stop, it affects braking capabilities, and the surge is most intense, and will possibly stall the jeep; unless I pub it in neutral where it will even out the idle a little bit.

Roler

And just as you thought nobody would respond and are still left down with this, I decided to bump you back to start....
You have a Renix, so I'll keep it short, for others to chime in.
Your stalling etc during driving and the idle issue, assuming that you did also clean out the IAC and grounds,checked for vaccuum leaks etc etc, could warrant a new CPS (take a good quality one).
Not sure what you mean with things affecting your braking capabilities..?

cruiser54

Did you use this to find the important grounds?

Renix Ground Refreshing

The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, failed emission tests, and wasted money replacing components unnecessarily.

The components grounding at the dipstick tube stud are:

Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.

The factory was aware of the issues with this ground point and addressed it by suggesting the following:

Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.

Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.

While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.

Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.

First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4” socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.

A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18” long with a 3/8” lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.

A further improvement to the grounding system can be made using a #4 cable, about 10” long with 3/8” terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.

For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.

If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.


Revised 03-04-2013


Have you checked to see if your intake manifold bolts are loose?

Roler

( I knew you wouldn't be far Cruiser, thats why I thought to keep it short, to make room for your copy/paste

cruiser54

I figured as much.

Roler

What are you saying, are we starting to get to know each other?

XJwonders

Guys. Get a room! Lol

Roler

Haha,...as I posted it, I thought....this may sound like we're in the wrong forum here... LOL

belvedere

Could you elaborate on this? Have you temporarily disconnected & plugged the vacuum line to the booster to see if things improve? Another possibility is the booster is good, but affected by a vacuum leak elsewhere. Your problem makes me think vacuum leak, but refreshing the grounds, as Cruiser suggested, is always a good idea.

salad

It sounds like you could have a vacuum issue but stupid automatics mess things up. It's possible that your engine is simply surging and, with the transmission engaged, it makes braking difficult - as opposed to a vac leak that results in a loss of power boost.

I don't see mention at all of you testing the TPS. This is absolutely critical combined with ECU an sensor grounds. It sounds like your TPS is worn at the shut position and producing an erratic signal.


You can also find sensor diagnostics here: http://www.lunghd.com/Tech_Articles/...iagnostics.htm

cruiser54

Salad, you need the newest version:


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

salad

December?! You sneaky...

cruiser54

Yep. While you were shaking the coal from your stocking..........

salad

Sorry chief I couldn't afford a stocking this year. Spent it all on the Jeep.

Windsor 90 Laredo

I did clean all the important grounds, re checked n cleaned them recently. My negative batt. Ground is on the engine bolt by the dipstick with all the other important grounds, rather than by itself. I assume that's ok? The braking issue was just due to the surge of an automatic in drive. This surge issue went away only to return, now I believe it's from the egr valve opening while at idle. The tps seems to do its job, but perhaps it needs more attention.