Renix woes

[camjeep3]

Ok guys, where to begin.

My truck has been running kind of rough lately. doesnt have a steady idle, lacks power, sounds terrible too. It got worse after A recent off road trip where the vac line pulled off the front axle. No water was pulled in or anything like that, but I ran sea foam through the system and it didnt seem to help. Next I did a full tune up with rotor cap wires and plugs. Still not there. I pulled the IAC off the throttle body and cleaned it. It had some hard buildup on it that i had to scrape off with my nail and shoot it with cleaner. Still not running where it needs to be though. My next plan of action is pull the TB completely and clean it up good and see where that gets me, as well as a new fuel filter for good measure. My question is after doing this, what should my plan of attack be? how would you go about diagnosing the problem? I can't explain well what the truck is doing but under load it doesnt sound right, and the idle is bouncy.

Sorry for the long post, but all help is appreciated

[ComancheKid45]

Checking the adjustment on the TPS (theres a writeup somewhere on here) sounds like a direction to take next. A new o2 sensor probably won't hurt either ;)

[cruiser54]

After a thorough throttle body cleaning and reinstallation with a new gasket, check your TPS as suggested. Also make sure your intake manifold bolts aren't loosened up along with checking your EGR operation.

Write-ups on TPS and EGR are below.

 

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

 

 

TESTING THE EGR VALVE FOR 87-90 4.0 ENGINE

 

Valve Opening Test

1) With engine at normal operating temperature and at idle,

rapidly open and close throttle. Open throttle sufficiently to obtain

at least 1500 RPM. Movement should be noticed in EGR diaphragm.

2) If diaphragm does not move, probable causes are: faulty

vacuum signal to EGR, defective EGR diaphragm or defective

backpressure sensor diaphragm (if equipped), or leaks in vacuum lines

or connections.

Valve Closing Test

1) With engine at normal operating temperature and at idle,

manually depress EGR valve diaphragm. RPM should immediately drop,

indicating that EGR valve is not leaking and had been properly cutting

off exhaust gas flow at idle.

2) If there is no change in RPM and engine is idling

properly, exhaust gases are not reaching combustion chamber. Check for

plugged passage between EGR valve and intake manifold.

3) If engine idles poorly and RPM is not greatly affected by

manually moving diaphragm up, EGR valve is not closing off exhaust gas

flow. Check for carbon between pintle, leaking EGR valve gasket or bad

EGR valve.

***************

[camjeep3]

Awesome info. I'll lOok into this after work. Thanks guys

[camjeep3]

cleaned the TB really good and it runs like it should now, it also doesnt have an unsteady idle now. It just idles high, I guess this has to do with my CPS? I drove it around and its idling about 1000 1100

[Pete M]

high idle might indicate vacuum leak somewhere. shouldn't have anything to do with the crankshaft position sensor. usually when that goes bad, the engine won't run.

[Comanche County]

http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm

[camjeep3]

high idle might indicate vacuum leak somewhere. shouldn't have anything to do with the crankshaft position sensor. usually when that goes bad, the engine won't run.

sorry pete. I meant TPS :roll: hmmm I guess I will start going though the vacuum lines and see what I come up with.

[Pete M]

a trick for finding vacuum leaks is to start the engine and carefully spray a flammable liquid (one that evaporates quickly, like starter fluid) along the lines and seams. an unlit propane torch works too. if you find the vacuum leak, the stuff will get sucked in and the idle speed will change.

 

obviously have the means to put out a fire close at hand :yes: , but I've not yet heard of anyone catching their truck on fire using this technique.

[comanchecravin]

they do make seafoam for you vacuum system i feel like that would be safer

[cruiser54]

they do make seafoam for you vacuum system i feel like that would be safer

 

Carb cleaner, propane, water are all fine as are a host of others.