Running Issues And Parts Questions?

[nhrocker]

Since I've owned my MJ I've been battling pesky little problems. Many of which I've figured out over time. Between the repairs, upgrades, and modifications I've done it's like a whole new truck, but it still has issues. For reference it's a 1990 MJ, 4.0 Renix, 5speed, NP231.

 

I'll start with the remaining issues.

 

Upon startup the majority of the time it starts fine. Once in a while it will either rev high (as high as 2000rpms) then drop down to normal, or start extremely low and take a while to speed up to normal idle. Out of starting it multiple times a day, every day, it will do one of those two conditions maybe a couple times a week.

 

The next issue is a high idle, but not consistent. When cold it does not idle high, but as it warms up, the idle increases. It used to idle at around 1500rpms consistently, but with work I've gotten it down to around 1200rpms. It doesn't always do this, some days it will idle at 1000rpms or less.

 

Those issues alone don't worry me too much, since during normal driving they don't seem to affect it at all. The biggest concern is a hesitation it gets at 50-55mph and above, when either holding speed or decelerating. It feels like a hesitation, stumble, mis, or something like that, which you can feel. The whole truck feels like it pulls back each time it does it, but it doesn't make any extra noises or anything. I've found if I'm going down a hill at any speed and leave it in gear to help hold speed down or decelerate it does a similar hesitation. It only seems to do this when up to temp.

 

Now onto what I've done so far. In working on the truck to repair and upgrade it I've replaced or modified a lot. Almost everything I've done has improved something about the way it drives or its performance.

 

For the intake, I made an adapter to run a conical oiled filter. It hooks into a HO throttle body I bored to 60mm straight through. The TB is bolted to an aluminum adapter/spacer to allow it to bolt on to the Renix intake manifold. I also made an adapter to allow the stock TPS to be bolted back on to the HO TB. Along with that I installed a later model HO valve cover with an upgraded gasket.

 

The EGR system has been removed and a blockoff plate was used on the side of the intake manifold. All vacuum lines relating to the egr, transfer case, and front axle have also been eliminated. What vacuum lines remained in the engine compartment have been either replaced or checked for leaks. So far I have not found any leaks (there could be some from movement/vibrations during driving). The valve system for the heater lines has also been eliminated. I still do not have heat, but believe it to be from a clogged heater core.

 

The catalytic converter has been removed, and a Dynomax Super Turbo muffler was installed with an elbow off the back of the muffler going throught the frame rail exiting just under the front of the bed.

 

It has recieved flow-matched 4 orifice fuel injectors, new IAC valve (old one came out in pieces), and new O2 sensor. While checking and resoldering the ground connections in the harness, I also added an extra ground direct to the firewall, as well as cleaned the grounds to the dipstick mount bolt on the block. I've replaced the oil pump with a high flow unit while in there doing a new rear main seal, as well as an upgraded oil pan seal. While in there I did find some large deposits in the bottom of the pan, no metal though. Roughly 3 to 4 tablespoons of deposits. I found no water in the oil, and have never found oil in the coolant.

 

When I first purchased the truck it never got up to operating temp. I found that someone had installed a 160 degree thermostat. I imediately replaced that with a 195*. I also converted it to an open system using an inline filler neck in a new upper radiator hose. After issues with that blowing hoses off I replaced the water pump, and put in another new 195* thermostat. It has been fine since and temps respond as they should, checking both the guage inside and verifying with an IR thermometer.

 

I have also been paying attention to the mechanical end of it. Both axles were replaced with a set of D30/Chry 8.25 out of a 99XJ with 4.10 gears. Both were fully cleaned/rebuilt as needed before install and within the past 2 months have been reopened and checked. They're in great condition. All u-joints have been replaced within the last 2 years or less. Transfer case was replaced a couple months ago as well. The only things that leaves I feel could have any affect on these issues is the transmission (I did drain and upgrade the fluid while swapping the t-case, fluid looked fine), clutch, or internal mechanical issues with the motor.

 

 

So I'm narrowing this down. Things have been improving. Like mentioned, it used to idle at 1500-1700rpms, and it also used to get the hesitation as low as 35mph. Somehow through all this work it is getting better. The fact that the issues are not conistent has me hoping its still just an electrical/sensor issue and not something mechanical.

 

I've pretty much decided to replace the TPS, since adjusting it doesn't seem to make a difference at all. I'm also thinking the MAT sensor and/or coolant temp sensor need replacing since many of the issues still seem to be temperature related. Thats where the confusion comes in.

 

I can't seem to find MAT sensors available anywhere. Am I looking for the wrong term? Parts stores and Rock Auto don't show them at all.

 

For the coolant temp sensor, everything I find seems to be the sender for the guages, not the one in the block. Again, looking in parts stores and Rock Auto has me coming up empty.

 

Then theres the TPS. When searching Rock Auto they show one under the 2.5 engine that looks identical to mine, and for less than $20. For the one that looks correct under the 4.0 its $106.79! Will the one for the 2.5 work on my 4.0?

 

Sorry for writing a book on this guys. Just hoping with as much info as possible someone out there can help me with this. I love my truck but am getting really frustrated with these issues.

[Eagle]

Fast idle on start-up is often caused by a dirty IAC (Idle Air Controller).

 

For the hesitation, I'd guess that you made too many mods to the intake and exhaust, and it's now flowjng enough that the 19-lb injectors aren't supplying enough fuel. The hesitation sounds exactly like what I felt in Bob Salemi's Renix stroker when he first put it on the road. He cured it with a set of HO injectors, IIRC.

[nhrocker]

The starting issue isn't the fast idle. It will briefly rev up to over 2,000rpms, but then drop back down to a normal idle. Other times it will start sluggishly and idle at around 200rpms. About 75% of the time it starts and idles fine. The fast idle only occurs after its been running for a little while and comes up to full temp. I originally thought IAC as well. When I pulled it to clean it it came out in pieces. I replaced it with a brand new one and it still does it. I believe the combination of new IAC and re-grounding the harness is what brought the idle at temp from 1500-1700 down to its current 1200rpms. Better, but still not where I'd like to be.

 

The injectors I used were purchased from Precision Auto Injectors. They are the upgraded 4 hole style that are rated for Renix or OBD1 HO motors (running stock 39psi at the fuel rail) already. I had called and spoken with him on the phone and listed all the modifications to my MJ and he was confident that larger injectors weren't needed unless I was going stroker or forced induction.

 

I don't think I'm reaching duty cycle on them, because its only under partial or no throttle that I have the hesitation. If I'm into the throttle more, either to accelerate or if I'm trying to hold speed up an incline, the issue completely goes away. I would think if I was at duty cycle already at partial throttle, wouldn't there be nothing more to give if I stepped on it? My thought process was if its throttle related TPS and o2 would be the largest culprits. Both appeared to be original. I used to get the hesitation as low as 35-40mph. When I unplugged the o2 and drove it for a couple weeks, it got rid of the hesitation below 50mph. I installed a new o2 sensor and the hesitation below 50 hasn't come back. So I was thinking the remaining hesitation over 50-55mph should be TPS related?

 

I was thinking if the $20 2.5L TPS from Rock Auto will work for my 4.0, I would pick it up. And with the high idle related to the engine temperature, either the coolant or manifold temp sender must be faulty. But those I can't even seem to find available at all.

[cruiser54]

TPS should be checked. It's probably bad.

Also, check the sensor ground circuit. There are some crappy crimps back up in the harness that affect multiple sensors.

 

Cruiser’s Renix Sensor Ground Test

 

This sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate.

Set your meter to measure Ohms. Be sure the key is in the OFF position. 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 runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.

You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well.

Revised 06/12/2012

[cruiser54]

^{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: With the Key OFF, and 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 only a flat three-wire TPS mounted on the throttle bodyand it provides data input to the ECU. It 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. 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.}

^{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, 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. 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 square four-wire connector side of the TPS.}

^{If you have ENGINE ISSUES check the flat 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 09-22-2012}

[nhrocker]

As mentioned in the first post, I've already opened and checked the harness grounds. I soldered the connections, and while there soldered in an additional ground that's connected to the firewall. Both the block to battery and block to firewall grounds have been upgraded to much larger cable with solid end lugs. Originally the grounds at the TPS and IAC were reading around 1.8ohms. I got them down to a very minimal number (can't remember what at the moment). It's a '90, so no c101 to worry about.

 

Sounds like I'm on the right track thinking the TPS is on its way out. I tried testing it in the past and couldn't get a good reading. I was thinking I might have been doing something wrong, but maybe it really is just faulty. You mention the auto TPS being usable, which is much better priced and available. I may just pick up one of those and try tuning that in instead of messing with mine anymore.

 

And no input on the temp sensors? Seeing that all my running/idling issues are temperature sensitive I'm pretty sure one if not both of them are faulty, but don't know why I can't find them available anywhere.

[cruiser54]

Get the TPS ruled out first.

[nhrocker]

Get the TPS ruled out first.

TPS is now brand new, and set properly. Ground at plug shows 0.0ohms. It made no difference in the hesitation or idle issues.

 

I did find excess oil in the TB and intake. I'm running a HO valve cover and grommets/hoses which are all clear, no plugged ports. The oil appears to be mainly coming out of the front hose off the valve cover which connects back to a barb fitting on the adapter I made to run a conical filter.

 

Since my last post I also had both the ignition switch and cylinder die. While sitting to replace those I found the fuel tank was leaking. It now has new ignition cylinder/switch, new gas tank/straps/pump/screen/filter/soft lines, and new spark plugs. The color on plugs 1 and 5 were a little darker, and when I checked they had just over a .040 gap. I know they were .035 when installed. New plugs set to .035 and the hesitation is still there, but didn't feel as bad to me (it may be just me hoping for any improvement at this point...).

[nhrocker]

Well, with the truck back on the road finally I had a chance to try some things. I've found that the hesitation will occur in any gear once its at or above 2,100rpms. Still only if its either holding speed or decelerating. If I'm into the gas at all it seems to go away till I let off.

 

It also doesn't like cold starts. It never had this problem before. If its cold at all I have to leave the hand throttle up a little to keep it idling or RPMs drop too much and it stalls out. Once its up to full operating temp it still idles between 1000 to 1400rpms.

[nhrocker]

So the hesitation got even worse. It was doing it as low as 1800rpms, and when it got really bad started bucking as well. I found that the fuel pressure regulator was junk when someone suggested I check it. I pulled the vacuum line off and gas started coming out. I just replaced it with a brand new one. The hesitation is still there, but is much less noticeable and it no longer "bucks" at all. It still only under decel or holding speed, issue goes away under full throttle.

 

The low idle on a cold start is still there. The colder it is, the worse it is. A few days this week it wouldn't stay running it was so low without giving it a little throttle. Once its up to temp its back to idling at 1500rpms again.

[cruiser54]

Worth a try. Remove your IAT and clean it carefully with a toothbrush and carb cleaner.

 

I wonder if someone,at some time, messed with the throttle body butterfly stop screw.

[Biotex]

On deceleration, and above 1200 rpms the system goes into open loop. In open loop, the A/F is determined primarily by the MAP, CTS and engine speed.

You stated you did not replace the coolant temperature sensors. I would start there...

[nhrocker]

Worth a try. Remove your IAT and clean it carefully with a toothbrush and carb cleaner.

 

I wonder if someone,at some time, messed with the throttle body butterfly stop screw.

Cleaning the IAT is worth a shot. I like free ideas at this point. I've dropped way too much money into fixing this with no real results yet. :???:

 

The stop screw itself has not been played with. It is not a renix TB just for reference. It's a HO off of a friends stock '99. I bored it out to 60mm myself. I did not mess with where the butterfly "seats" so to speak. Only took off the restricted section. It's sitting on a .538" thick aluminum adapter I also machined to 60mm to match the TB.

On deceleration, and above 1200 rpms the system goes into open loop. In open loop, the A/F is determined primarily by the MAP, CTS and engine speed.

You stated you did not replace the coolant temperature sensors. I would start there...

The coolant temp sensor was one of my earliest questions. The one on the top/rear of the head for the gauges was replaced when I first got the truck and swapped in a full gauge cluster. The one on the side of the block looks original and no parts store in town even lists/shows a replacement for some reason. I believe I've found the correct one through Rock Auto (the one with the two wires coming out to a plug).

 

It's around $17, so not too bad for me to try. Truck is about to hit 180k miles, so it would need to be replaced at some point anyway. Can you tell I'm used to trying to justify why I'm willing to do what I do to my Jeeps? :cheers:

[nhrocker]

I need to give a HUGE thank you to cruiser54 and his Renix tips! Thanks to him I finally have good news, the hesitation is gone!

 

I spent a lot of time doing research on my problems, and things kept relating back to timing issues. On the suggestion of a friend I had pulled the cap/rotor to inspect them and found burn marks. They had only been in there for about a year. All the internals of the distributor looked corroded and it seemed to have more play than what I would expect, so I ordered a new one. Since the new one came with a new cap/rotor, I cut open my old one to check the indexing of the distributor, per cruiser's write up. Guess what, it was WAY off, about 3/8" off actually. So after cutting the tabs off the new one, properly indexing with a set of feeler gauges, and installing the new cap and rotor, it no longer has the hesitation!

 

It still has a problem with cold starts and a 1500rpm high idle once its up to temp, but I haven't touched the temp sensors yet. I also picked up a new intake/exhaust manifold gasket to try at some point. I haven't been able to find any external vacuum leaks, but I'm wondering if it's leaking between one of the exhaust ports and an intake port.

[cruiser54]

Cool news. Was the cap that only lasted a year one with aluminum instead of brass terminals?

 

Looks like you need to test the TPS on the engine side (flat connector) next and check the sensor ground circuit while you're at it.

[nhrocker]

Cool news. Was the cap that only lasted a year one with aluminum instead of brass terminals?

 

Looks like you need to test the TPS on the engine side (flat connector) next and check the sensor ground circuit while you're at it.

Yes, it was aluminum terminals. If they were brass they may have lasted longer, but it still would have been just a "band aid" over the real problem.

 

I mentioned earlier in the thread (somewhere in the encyclopedia's worth of text I wrote) that I've soldered the sensor ground circuit splices, cleaned the connections on the block, and added an additional ground to the firewall. The block to firewall and block to battery grounds have also been upgraded. The new TPS tests perfect and the ground on the flat plug now reads 0.0 ohms.

[cruiser54]

Anybody ever screwed with the throttle butterfly stop?

 

Intake manifold bolts tight?