86 2.5 Periodically Runs Poor

[87Warrior]

I tested my grounds prior to doing the ground refresh. I unplugged all sensors I could around the intake to check the grounds.

 

Before (ohms)

Firewall - Battery: 1.5

Head bolt (strap) - Battery: 1.7

All sensors - Battery: 1.6

All sensors - Dipstick: 1.5

 

After (ohms)

Firewall - Battery: 0.9

Head bolt (strap) - Battery: 1.2

All sensors - Battery: 1.3

All sensors - Dipstick: 1.2

 

Hard to say if it helped as the temperature this afternoon was almost 70. My coolant temperature gauge still read 140 on a hot motor after a test drive.

[cruiser54]

And the cold weather performance?

[87Warrior]

cruiser54, on 02 Dec 2013 - 18:22, said:

And the cold weather performance?

Unable to determine at this time. A cold front is forecasted to come through on Wednesday so I hope to give her a try then.

 

Is there any way to test the CTS with an ohm meter?

Is there any way to test the MAP with an ohm meter and vacuum pump?

 

When unplugging sensors on the intake, I determined the CTS is at the rear side of the intake manifold. There was another sensor threaded into the manifold, on top, inline with the #3 cylinder intake runner. Any idea what that one could be? My thought was Incoming Air Temperature, but was unable to find one listed for the Renix 2.5.

[cruiser54]

There is a test for both and I have a chart with ohms values. Unfortunately, I have not ventured into posting photos here.

I'll email it to hornbrod and see if he'll post it up in this thread.

Unscrew the IAT and have a look at the tip. If real dirty, it can cause some issues and can be cleaned carefully with carb cleaner.

[Comanchemodder]

There was another sensor threaded into the manifold, on top, inline with the #3 cylinder intake runner. Any idea what that one could be? My thought was Incoming Air Temperature, but was unable to find one listed for the Renix 2.5.

 I believe that is the manifold air temperature sensor (MAT).  In the attached link it describes this sensor about half way down the page.

 

http://www.4wdmechanix.com/Tuning-and-Troubleshooting-the-2.5L-Jeep-TBI-Four.html

 

From the link:

 

The manifold air temperature (MAT) sensor threads into the intake manifold. This signal indicates the air/fuel temperature in the intake manifold. The resistance should read less than 1000 ohms with the engine warmed to normal operating temperature. Check resistance between the two MAT sensor plug contacts. Though not as accurate as a mass-air flow sensor, the MAT signal proves valuable in helping the ECU set proper fuel flow and spark timing under various engine and atmospheric conditions.

[cruiser54]

 

There was another sensor threaded into the manifold, on top, inline with the #3 cylinder intake runner. Any idea what that one could be? My thought was Incoming Air Temperature, but was unable to find one listed for the Renix 2.5.

 I believe that is the manifold air temperature sensor (MAT).  In the attached link it describes this sensor about half way down the page.

 

http://www.4wdmechanix.com/Tuning-and-Troubleshooting-the-2.5L-Jeep-TBI-Four.html

 

From the link:

 

The manifold air temperature (MAT) sensor threads into the intake manifold. This signal indicates the air/fuel temperature in the intake manifold. The resistance should read less than 1000 ohms with the engine warmed to normal operating temperature. Check resistance between the two MAT sensor plug contacts. Though not as accurate as a mass-air flow sensor, the MAT signal proves valuable in helping the ECU set proper fuel flow and spark timing under various engine and atmospheric conditions.

MAT and IAT are interchangeable terms in the Renix world. Hopefully the chart shows up in this thread today. 

[Oyaji]

If you have access to an exhaust gas analyzer, you could disconnect sensors and manually substitute known good values as you check the effect of each sensor in turn to isolate (a) bad one(s), but I am guessing that is beyond the capability of most owner/mechanics.

 

I think you should start by fixing what you know is broken and could be the source of your problem rather than starting to replace things that seem to be functioning fine (after all, you did report good running and plenty of power, with just an intermittant problem). Despite the comments that deny or minimize the value of understanding the background of how things actually work and instead endeavor to derail the quest for a fix for the problem at hand, it is no less true that understanding the way things work really does help in troubleshooting and finding the solution to a problem.

 

If after replacing your cracked exhaust manifold you still have the problem, you are no worse off for having completed an easy repair you had to do in any case, and can still continue checking other avenues of solving the problem at hand. If it fixes the problem, you are saved what would otherwise have been a fruitless task of exploring what would have been dead-end avenues.

 

Please keep us updated and let us know of the solution you find.

[HOrnbrod]

Here they are:

 

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FWIW, a few years ago I installed a threaded bung in my CAI tube and installed an additional IAT sensor there. During the summer I plug the IAT connector into this location; then back to the manifold for the winter. It seems to help mileage marginally and smooth the idle a bit, but it's not earth shattering. Might help more with the Renix.

[87Warrior]

Oyaji - I do agree the manifold should be replaced. A new one should be arriving on my door step within a few days. I doubt, however, it will be easy. I suspect a rusty bolt or stud will break off in the head and I will have to remove the head to remove broken bolt. With the head removed I will probably want to take it to the machine shop to get it decked with a few new valves (as needed) and new seals and guides installed.

 

Don - Thanks for the chart. I will remove, test and clean the IAT/MAT this evening. I notice the Renix era IAT/MAT sensors are no longer available but a folks seem to have good luck using early HO sensors.

[Oyaji]

Couple of practical suggestions for you:

 

Use of a good penetrating oil will reduce the chance of twisting off a stud; chase it with a heavier oil as you disassemble. Also take care to wire-brush the threaded potion of any fastener you can reach; doing a good job there will help get the nut off more easily. Finally, be patient and move the nut only a little, alternately tightening it after every bit you loosen it. "Rocking" the nut back and forth will work it loose by stages, and minimize the risk of twisting it off. Replace the nuts with (1-use) copper-coated nuts to make disassembly easier next time, too.

 

Also, for any vehicle you plan on keeping for the long term, it pays to have back-up parts in your own inventory for when it's time to work on it. A spare head would allow you to spec it out to your satisfaction during your spare time (porting including match-porting the manifolds if you have spares of them too, "CCing" the combustion chambers, and multi-angle valve jobs come to mind here. :)). A head swap is much less time consuming when you don't have to wait for the machinist, and cuts the amount of time your vehicle is off the road.

[HOrnbrod]

Don - Thanks for the chart. I will remove, test and clean the IAT/MAT this evening. I notice the Renix era IAT/MAT sensors are no longer available but a folks seem to have good luck using early HO sensors.

 

Brett, here's the IAT/MAT temp vs. ohms chart for the early HOs. This is from the 91 FSM. As you can see, the ohm values are quite different throughout the temp range. I don't know how well this sensor would work in a Renix system, and how much weight is assigned for the IAT signal by the Renix computer. Aren't the connectors different too? The Renix and HO IAT's are completely different animals.

 

I think cleaning the tip up with Berryman's carb cleaner and a Q-tip would be best to try first. Ans aftermarket IAT sensors are still available as I'm sure you know. HTH..........

 

 

[87Warrior]

Houston, we have a problem. The MAT sensor will not ohm out, at all. If I 'jump' the contacts in the tip of the sensor the ohm meter responds. I tried to see if I could get a reading by applying heat with a heat gun, no go. I also put the MAT in the freezer for 1/2 hr, no go.

 

I have scoured all parts stores and can not find a MAT/IAT listing for the 86 2.5 Renix.

[HOrnbrod]

Ah yes, part number 33002382. I have searched for these before and could not find one. All the TBI 2.5's through 1989 used this sensor. Some Dodges and Plymouths too.

 

Have you seen this? It's a good article on that MAT sensor and it does list a substitute that looks like it might work for the TBI engine.

 

http://forums.4wdmechanix.com/topic/225-jeep-yj-wrangler-25l-tbi-troubleshooting/

[cruiser54]

Oyaji - I do agree the manifold should be replaced. A new one should be arriving on my door step within a few days. I doubt, however, it will be easy. I suspect a rusty bolt or stud will break off in the head and I will have to remove the head to remove broken bolt. With the head removed I will probably want to take it to the machine shop to get it decked with a few new valves (as needed) and new seals and guides installed.

 

Don - Thanks for the chart. I will remove, test and clean the IAT/MAT this evening. I notice the Renix era IAT/MAT sensors are no longer available but a folks seem to have good luck using early HO sensors.

If it tests bad, clean it before replacing it. 

 

And, I THINK the CTS and MATs are the same as the 4.0.

 

I wouldn't rush out and procure a spare head, exhaust analyzer, penetrating oil or copper coated nuts, and I'd hold off on the manifold since you've discovered through proper testing procedure that the MAT is not working. 

[HOrnbrod]

Found a NOS Mopar unit on Ebay here:  http://www.ebay.com/sch/6000/i.html?_nkw=33002382&_dmpt=Motors_Car_Truck_Parts_Accessories&_rdc=1

 

Last one in the civilized world.  :yes:  Appears the seller knows it too.

[Comanchemodder]

About a year ago when refreshing my 2.5L I debated replacing that MAT, but at the time my MAT "seemed" okay with resistance in the 1000 ohm range at operating temp.  Not knowing much about MAT, I just figured they were pretty much created equal and at the time found a company which seemed to make an equivalent.  They state 100k Ohm @ -40F and 50 Ohm at 300 F, which kind of matches Hornbrod's table for RENIX.  Today, I sent them an e-mail requesting a couple more data points in the operating range.  I will re-post if they seem favorable.  At first glance, the sensor seems a closer match than the HO unit.  $30 minimum order is kind of expensive to "try" however.  Also, please confirm the 3/8" NPT thread is correct.

 

http://www.injector.com/cart/pc/Air-Charge-Temperature-Sensor-Part-No-1814-12p65.htm

[Oyaji]

 

Don - Thanks for the chart. I will remove, test and clean the IAT/MAT this evening. I notice the Renix era IAT/MAT sensors are no longer available but a folks seem to have good luck using early HO sensors.

 

Brett, here's the IAT/MAT temp vs. ohms chart for the early HOs. This is from the 91 FSM. As you can see, the ohm values are quite different throughout the temp range. I don't know how well this sensor would work in a Renix system, and how much weight is assigned for the IAT signal by the Renix computer. Aren't the connectors different too? The Renix and HO IAT's are completely different animals.

 

I think cleaning the tip up with Berryman's carb cleaner and a Q-tip would be best to try first. Ans aftermarket IAT sensors are still available as I'm sure you know. HTH..........

 

 

Image Not Found

 

 

FYI: that chart has Fahrenheit and Celsius headings reversed - make sure to remember that if you ever use it.

[Oyaji]

About a year ago when refreshing my 2.5L I debated replacing that MAT, but at the time my MAT "seemed" okay with resistance in the 1000 ohm range at operating temp.  Not knowing much about MAT, I just figured they were pretty much created equal and at the time found a company which seemed to make an equivalent.  They state 100k Ohm @ -40F and 50 Ohm at 300 F, which kind of matches Hornbrod's table for RENIX.  Today, I sent them an e-mail requesting a couple more data points in the operating range.  I will re-post if they seem favorable.  At first glance, the sensor seems a closer match than the HO unit.  $30 minimum order is kind of expensive to "try" however.  Also, please confirm the 3/8" NPT thread is correct.

 

http://www.injector.com/cart/pc/Air-Charge-Temperature-Sensor-Part-No-1814-12p65.htm

 

 

Connect 3 of them in series and it would be a lot closer to proper resistance, it appears.

[HOrnbrod]

Image Not Found

 

FYI: that chart has Fahrenheit and Celsius headings reversed - make sure to remember that if you ever use it.

 

Noted and corrected on original. Good catch.

[Jeep Driver]

My 2.5 runs fine.

 

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[HOrnbrod]

Guess you know that the MAT sensor for the MPI engines?

[Jeep Driver]

Guess you know that the MAT sensor for the MPI engines?

Yeah, I know.

 

But it's what's available........that was well over a year ago and it still runs well.

[gogmorgo]

Found a NOS Mopar unit on Ebay here:  http://www.ebay.com/sch/6000/i.html?_nkw=33002382&_dmpt=Motors_Car_Truck_Parts_Accessories&_rdc=1

 

Last one in the civilized world.  :yes:  Appears the seller knows it too.

He's in Canada. That's not a particularly outlandish price up here...

[87Warrior]

Don - That would be the sensor. The eBay sellers price is on target with the going rate for a 2.5 Renix CTS.  :nuts:  I did come across that troubleshooting thread, was a good read. Waiting to see the final result. 

 

If it tests bad, clean it before replacing it. 

 

And, I THINK the CTS and MATs are the same as the 4.0.

 

I wouldn't rush out and procure a spare head, exhaust analyzer, penetrating oil or copper coated nuts, and I'd hold off on the manifold since you've discovered through proper testing procedure that the MAT is not working. 

I did clean the MAT with carb cleaner and Qtip. A lot of black gunk came out. After the cleaning I could not get it provide any resistance. 

 

No worries on me jumping into the manifold replacement  :wrench:

 

My 2.5 runs fine.

 

<snip>

I tried something like this tonight. Stole the IAT sensor off a non running 4.0HO, cleaned it, then cut a pigtail off of a junk engine harness. Spliced the 4.0HO pigtail to the 2.5 Renix MAT plug. The pigtail ohm'ed to 1600 at 70 degrees. 

 

The truck idles a touch smoother with the new set up. I noticed the truck idled the same as always with either MAT disconnected. Tomorrow I will know if any of this has done any good with a forcasted high of 30 degrees. 

[HOrnbrod]

 

Found a NOS Mopar unit on Ebay here:  http://www.ebay.com/sch/6000/i.html?_nkw=33002382&_dmpt=Motors_Car_Truck_Parts_Accessories&_rdc=1

 

Last one in the civilized world.  :yes:  Appears the seller knows it too.

He's in Canada. That's not a particularly outlandish price up here...

 

You're right, that's not a bad price. It retailed for a bit over $50 when they were plentiful. Shipping seems a bit high, but maybe that's how it is with Postes Canada.  :dunno: