cruiser54

Yes, it will and will be fine. Run a quality oil filte rlike Wix or Napa gold and some good oil.

Never had this before?

Hang on for a bit. We'll likely soon get a complete term paper on the evolution of sending units.......

Vacuum leaks could affect it as could a dirty throttle body and IAC. Have you ever cleaned the TB and IAC? Did you do the sensor ground test before adjusting the TPS?

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.

Dave, click on the link in my signature and do the Ground Refreshing, Connector Refreshing, and the C101 Refreshing. Seems like you might have a burned terminal at the ignition switch brown wire terminal also. CPS can be tested also. That's also in the link.

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.

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.

Hope we haven't lost him, and I use the term "we" loosely.

Getting back to the OP's questions, which Ford 4-holers injectors do you have? If you have the 24# version on a non-aspirated stock engine, they will not help your MPG, especially with the Renix computer. Also have you checked your fuel pressure at the rail with a gauge set, and what gear ration are you running? Why would we want to do that? Stick to the subject at hand, that is. Isn't this forum turning from a "help the guys out" forum into an ego driven pontificating distraction instead?

That doesn't answer my question.

And the cold weather performance?

Was the speed limit 55 in 1987? It was 65 here in Arizona.

Maybe it is on the intake. I've got a brand new one up in the attic with a throttle body and stuff on it. I should go look. Do the sensor ground test while you're at it. 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

The CTS on a Renix 4.0 is in the lower left block and the temp sender for the gauge is at the back of the head on the same side. The Renix Jeeps will run acceptably with a bad O2 sensor. many folks wuldn't even notice. A MAP sensor on the other hand has a major part in fuel/air ratio. Second in line is the CTS, followed by the Intake Air Temp sensor, The reason I'm encouraging the ground refreshing is that the CTS, TPS, IAT, and MAP share the same ground circuit terminating at the engine dipstick tube stud. If the grounds are bad, so are the signals sent to the ECU. We took it upon ourselves to clean the firewall ground, especially on the 4 cylinders at first opportunity, due to the excellent results we got in drivability.

I've got them in Prescott.

I just grabbed that part out of an XJ at the JY and it fit perfectly into my MJ. $14. Even came out of a Laredo with rocking seats. Same part number on it, too.

But it runs okay in warm weather? That kinda rules out all this O2 sensor stuff and exhaust cracks then, doesn't it? The 4 cylinder TBI engines have an issue with cracking/split vacuum lines near the throttle body. That will screw with the MAP sensor which can cause a drastic change in air/fuel ratio much greater than a failed O2 sensor. Regardless, do the ground refreshing. You have my instructions? They're for the 4.0 for the most part, but they do share some commonalities and it's worth doing.

He's had the crack for awhile. If the sensor was in a single tube or before all the tubes come together, maybe. Even so, the OP's issue is new.

I suspect the coolant sending unit must be bad. The tstat housing read 198 on a hot, running, motor with an IR heat gun, so I know it is running at the proper operating temperature. As I understand it, the Renix 2.5 has a gauge sending unit and a ECU sending unit. I plan to replace them for good measure, but am doubtful they will cure the issue.I have not removed and cleaned the braided strap from the firewall-head bolt or cleaned up the two dispstick grounds. I plan to do that the first chance I have. I do realize that a cracked manifold can lead to inaccurate O2 readings resulting in poor fuel mileage, etc. I doubt that a 20 degree drop in air temperature would cause so much of an issue with something that regularly has 400+ degree exhaust flowing through it. Progress. Keep in mind that the Coolant temp Sensor grounds at the dipstick tube stud as do other critical sensors. Don't wait to refresh the dipstick tube stud grounds or the braided strap. Actually wouldn't hurt to clean the strap and it's contact point at the engine side also. The theory of exhaust pulses should be at the bottom of your list or better yet, not even on it.

I think we need to stick to the original poster's issue at hand and help him get his Jeep fixed. Practical solutions are what this community is looking for, not heady pontificating responses that just muddy the waters and inflate people's own egos. Isn't that what we're about here?

I'm not sure it does. With 3 to 5 more cylinders in the equation, I don't see how a vacuum can be created by 1.

I'm not buying it because that theory is for a one cylinder two stroke engine. On an inline 4, there will always be pressure there. Ever hold your hand over a tailpipe? Did you feel anything pull your hand closer to the pipe? No. I've done the dollar bill test numerous times to check for burned exhaust valves. If none are burned, the dollar bill will NEVER get sucked up to the pipe.

Yep. I'll bet that's what it is.

Why is the coolant temp so low? Should be about 190*. Renix O2 sensors go into closed loop very quickly, generally in less than a minute regardless of thermal conditions. Ever taken that braided strap off the firewall and cleaned it up real well as well as scrape the paint off the firewall? I have a hard time subscribing to cold air getting into an exhaust manifold which is under pressure......