1986 TBI 2.5 no start/crank

Hey Y'all,

I am still stumped. I have been trying to get my 1986 4cyl TBI 2.5 started for the past three months!!

Here's what happened:
I was driving down the road and the car died. I have had it die while idling before, but never while giving it gas. So I tried to start it and nothing happened. Towed it home. Decided to check spark and found my #1 Cyl plug was bent at the end, as if the piston or something had hit it. They are champion coppers and were the correct length. After replacing spark plugs and wires I verified I had a strong, blue spark, fuel, and compression. I verified spark by removing the plug, reattaching it to the wire, and holding it against a ground while a buddy cranked it. I verified fuel by not only watching the injector spray fuel into the throttle body while it was being cranked (TBI!!) but also spraying starter fluid into the throttle body while it was being cranked. The latter did 'rev' it up a bit more and made it 'closer' to catching, but it still wouldnt start.

Verifying both fuel and spark, I checked the cap and rotor. (I had a problem with the distributor and timing before, but that was solved.) They are both good and functional.

Deciding it was a sensor, I replaced the Stepper Motor (Equivalent to an AIC valve). When that didn't work I took off the throttle body, scrubbed it hard, replaced the TPS, and put that back on. Nothing. I replaced the CTS but realized later that the one I replaced was for the gauge inside the cab and not the ECU. I am willing to replace the CTS for the ECU but I can't seem to find it. Online and in Haynes it says on the drivers side of the block, but I don't see anything down there. (BTW the reason I replaced these sensors is I was told by a mechanic friend that these were the most likely culprits, in the order I replaced them.)

I posted here and someone suggested the CPS, despite the fact that I had both fuel and spark. Replaced that, still no start.

So, to summarize, I have replaced:
CPS
TPS
Stepper Motor
plugs
wires
fuel filter
fuel regulator
Coolant temp sensor (For gauge, accidentally.)

How have you verified timing?

I haven't since it starting not running. To do so I would just set #1 to TDC and check the position of the rotor, no? It should be at cyl 1, right? I could do that tomorrow.

Cut a window in an old dist cap at #1. Set #1 TDC on compression stroke, verify compression.


Look up- indexing 2.5/4.0

I'd double check the timing. I guess if you've got good compression the timing chain hasn't broken

This 86 is essentially a renix right ? Any renix problems that might explain this?


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No it is not a Renix. Renix started in 1987. His is a throttle body injection abortion with 50,000 vacuum lines and gadgets attached to the throttle body.

I had one we played with about 6 years ago.

Lets start here.

https://www.google.com/search?q=jee...jection+vacuum+hose+diagram&ie=utf-8&oe=utf-8

I suspect it is bad timing. I have no idea what kind of timing advance they used, but my older cars used a vacuum advance and a centrifugal spring in the dizzy.

Could be flooding if the injector is feeding too much fuel, or low fuel pressure, too little fuel????

I had no start issues and idle speed issues from a bad IAT, Intake air temp sensor, but I do not know if the 86 had any kind of computer at all?

Green Mesa XJ said:

I'd double check the timing. I guess if you've got good compression the timing chain hasn't broken

This 86 is essentially a renix right ? Any renix problems that might explain this?


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Click to expand...

OK scratch that link, maybe this one?

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=0ahUKEwi23bLzztvSAhUGy2MKHWe7DRsQjRwIBw&url=http%3A%2F%2Fwww.jeepforum.com%2Fforum%2Ff8%2Fneed-help-fuel-system-wires-vac-lines-beer-me-677648%2F&bvm=bv.149760088,d.cGc&psig=AFQjCNF2t96VCLMjw476LkfmCuw4I_PHww&ust=1489774027235052&cad=rjt

They do not seem to be well labeled, and Google seems to pulling up all sorts on non jeep stuff

Yep that is a cj 1987 throttle body here is the thread

http://www.jeepforum.com/forum/f8/need-help-fuel-system-wires-vac-lines-beer-me-677648/

Well I'll be a suck egg mule, I just learned something real interesting.

http://www.4wdmechanix.com/Tuning-and-Troubleshooting-the-2.5L-Jeep-TBI-Four?r=1

Seems the 2.5 L had most of the Renix sensors, maybe even a computer as well? EDIT: Yes he claims the 86 was the first Renix year for the 2.5 Liter. But it was a throttle body injected, not MPI, Multi Port Injected like the 4.0s. The 4.0 MPI started in 1987

But I thought my 85 was non Renix, just a carburetor version upgraded to throttle body with all the old out of control Medusa looking carburetor control crap on it.

Green Mesa XJ said:

I'd double check the timing. I guess if you've got good compression the timing chain hasn't broken

This 86 is essentially a renix right ? Any renix problems that might explain this?


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Click to expand...

I need you to elaborate on this

" (I had a problem with the distributor and timing before, but that was solved.)"

Are you sure that the spark is f=not firing on the exhaust stroke instead of the compression stroke?

The 2.5L 85 had a Carter YFA carb on it. The carb had what they called a Solevac that controlled the jet in the carb. They had a very common problem that I ran into. It also used an electric choke. The issue was with the hold down on the plastic piece with the heater inside. The hold down would corrode and the heater path for the choke would go bad, such that the heater didn't work and the engine would always run horribly rich. If it is running rich, pull off the plastic cover on the electric choke and use a twist tie to hold the choke open and see if things improve.

I put the 86 tbi on the 85 motor. It worked great. From years of working on these engines, I have constantly seen vehicles that did not start, get flooded. For some reason, this engine, including the 4.0 tend to wet foul the plugs and they simply won't fire even after they are "dried" out. I always keep a cheap set of Champion plugs around for just this reason.

Interesting, that reminds me on the 87-9? and maybe on his 86, if it is flooded, cranking the engine with the gas pedal floored, at WOT, tells the ECU to cut off the injectors and it dries the plugs quickly and easily. That tells you pretty fast if it was flooded when it fires up after cranking at WOT for about 20-30 seconds, then at idle if fires and catches.

old_man said:

The 2.5L 85 had a Carter YFA carb on it. The carb had what they called a Solevac that controlled the jet in the carb. They had a very common problem that I ran into. It also used an electric choke. The issue was with the hold down on the plastic piece with the heater inside. The hold down would corrode and the heater path for the choke would go bad, such that the heater didn't work and the engine would always run horribly rich. If it is running rich, pull off the plastic cover on the electric choke and use a twist tie to hold the choke open and see if things improve.

I put the 86 tbi on the 85 motor. It worked great. From years of working on these engines, I have constantly seen vehicles that did not start, get flooded. For some reason, this engine, including the 4.0 tend to wet foul the plugs and they simply won't fire even after they are "dried" out. I always keep a cheap set of Champion plugs around for just this reason.

Click to expand...

Alright, a lot of replies, I will try to answer everyone. If I miss someone call me out.

Green Mesa, I don't have an old dist. cap lying around, can I do it without messing up my current cap?

Ecomike, mine definitely has an ECU and is a renix. I have all the sensors a regular renix has as far as I know. And to clarify, I was doing regular maintenance and tried to replace my rotor but it was rusted onto the distributor. SO in the process of getting it off I broke my distributor (an inch of vertical play). I took it out without marking it and could not get the new distributor to work and get on the right tooth. Sent it to a shop and they fixed it right up, got it running good, better than it ever has in fact. That was about 4-5 months ago, and it has been running fine since then, havent messed with the timing since.
I don't know how to tell if the plugs are firing on the compression stroke or not.

If the WOT sensor is broken would that not dry the plugs? I have tried starting it with the peddle to the floor and everywhere in between.

Great feed back and congrats on having one of the oldest and most fuel efficient Renix jeeps ever made. I am jealous.

OK, so we 100% rule out the timing as an issue now. The WOT sensor is the end of the TPS sensor itself. It too can be tested with an ohm meter. PM your email and I can get you the testing process data in a pdf.

Also go to Cruiser54.com and you will find a treasure trove of testing and mini-fixes... how toos on our Renix rigs.

The first thing to verify before testing sensors, is to test the sensor grounds one at a time!!!! Anything over 1 ohm from the sensor to the battery negative post on the ground wire is a problem. Make sure all the vacuum lines are properly connected and air tight.

Then test the FPR vacuum connection end for any sign of fuel (if you find gasoline or smell gas it is one of the problems or the problem), and test the IAT Temp sensor, O2 sensor, MAP sensor, and CTS temp sensor and lastly the TPS sensor. Also you should test the fuel pressure early to make sure it is between 29 and 39 psi while the pump is running (cycling the ign switch triggers a pump timer for about 3-4 seconds) or the engine is running. Low fuel pressure might kill atomization and make flooding easier, or high pressure deliver too much fuel.

I listed them in order based on the most likely, imho, to cause the flooding no start and rich operation wet carbon film on ALL the spark plugs.

Bad O2 sensor or O2 sensor network, wiring, relay etc will not cause a no start. It should start with the TPS disconnected and O2 sensor disconnected. I know a bad or dirty IAT temp sensor in the intake manifold will cause your issues. Funky ground wires to sensors will cause every know sort of gremlin there is, LOL

The IAC valve does need to be working and set properly by the ECU and shut timer....

How can we rule out timing if I haven't checked it, or are you assuming it isn't it since I haven't messed with it since my distributor broke?

I have a separate WOT, I am not sure what you mean that its on the end of the TPS... I will PM you for that info.

Damn, that website is great, I will use it to test the sensors. Could you clarify this: "Anything over 1 ohm from the sensor to the battery negative post on the ground wire is a problem." Are you saying to use the negative battery post and the positive on the sensor to test it?

I did replace the FPR when I cleaned the TB, but I will check that too. I will test those sensors, I assume by using the positive on the sensor and the negative on the battery?

I have tested the fuel pressure on a MPI, but isn't checking it different on the TBI?

What is an IT temp sensor? If everything else fails I will clean my grounds, will probably do it anyway.

This model of Jeep has no IAC, instead it has a Stepper Motor, which I have replaced.

stardust2280 said:

How can we rule out timing if I haven't checked it, or are you assuming it isn't it since I haven't messed with it since my distributor broke?

I have a separate WOT, I am not sure what you mean that its on the end of the TPS... I will PM you for that info.

Damn, that website is great, I will use it to test the sensors. Could you clarify this: "Anything over 1 ohm from the sensor to the battery negative post on the ground wire is a problem." Are you saying to use the negative battery post and the positive on the sensor to test it?

I did replace the FPR when I cleaned the TB, but I will check that too. I will test those sensors, I assume by using the positive on the sensor and the negative on the battery?

I have tested the fuel pressure on a MPI, but isn't checking it different on the TBI?

What is an IT temp sensor? If everything else fails I will clean my grounds, will probably do it anyway.

This model of Jeep has no IAC, instead it has a Stepper Motor, which I have replaced.

Click to expand...

You need to check your timing before anything else.

stardust2280 said:

How can we rule out timing if I haven't checked it, or are you assuming it isn't it since I haven't messed with it since my distributor broke?

I have a separate WOT, I am not sure what you mean that its on the end of the TPS... I will PM you for that info.

Damn, that website is great, I will use it to test the sensors. Could you clarify this: "Anything over 1 ohm from the sensor to the battery negative post on the ground wire is a problem." Are you saying to use the negative battery post and the positive on the sensor to test it?

I did replace the FPR when I cleaned the TB, but I will check that too. I will test those sensors, I assume by using the positive on the sensor and the negative on the battery?

I have tested the fuel pressure on a MPI, but isn't checking it different on the TBI?

What is an IT temp sensor? If everything else fails I will clean my grounds, will probably do it anyway.

This model of Jeep has no IAC, instead it has a Stepper Motor, which I have replaced.

Click to expand...

You have a switch on the TBI itself, correct?


How did you set the fuel pressure when you swapped the regulator?

stardust2280 said:

How can we rule out timing if I haven't checked it, or are you assuming it isn't it since I haven't messed with it since my distributor broke?

I was concerned you might have installed the Dizzy based on TDC at the exhaust stroke instead of compression, it which case it would have never started and run. You would have a weird crank sound if the timing chain was busted.

I have a separate WOT, I am not sure what you mean that its on the end of the TPS... I will PM you for that info.

In that case the WOT switch could be bad, and could be a problem or the problem. With out the manual I have no idea for sure if can cause a no start, but it could keep WOT cranking from drying out the engine!!! It should be an on/off electrical switch, easy to test with an ohm meter. On later Renix rigs the ECU sees WOT on the TPS sensor. They have no separate WOT switch.

Damn, that website is great, I will use it to test the sensors. Could you clarify this: "Anything over 1 ohm from the sensor to the battery negative post on the ground wire is a problem." Are you saying to use the negative battery post and the positive on the sensor to test it?

Yes on the negative battery post, but the other end needs to be just the wiring harness ground connection at each sensor. I disconnect the sensor and test the loose ground connector (not positive) on the harness to the battery negative post to avoid errors.

I did replace the FPR when I cleaned the TB, but I will check that too. I will test those sensors, I assume by using the positive on the sensor and the negative on the battery?

NO, the ground on the sensor is the sensor connector harness wire that connects to the battery negative post. Just disconnect the sensor. One wire should read under 1 ohm, the other wire should have a huge Ohm resistance (ignition must be OFF!!!!!).

I have tested the fuel pressure on a MPI, but isn't checking it different on the TBI?

Seems it is, and may be 14-15 PSI from 3 refereces I found so far. http://www.4wdmechanix.com/Jeep-Fuel-Pressure-Requirements?r=1

Yes that may be, so you need to check the 86 TBI fuel spec then. Where is the fuel pump? Is it on the side of the engine block running off the Cam shaft or in the gas tank?

What is an IT temp sensor? If everything else fails I will clean my grounds, will probably do it anyway.

The Renix 4.0 Jeeps had their worst ground problem on the sensor wire contacts near the oil dip stick bolt passenger side near the oil filter area.

The IAT is an Intake manifold Air Temperature sensor. The ECU uses it and the MAP sensor data and to some extent the CTS temp data and TPS data to set the fuel rate for cranking. I had a bad/dirty one, they can be cleaned!!!!, that caused temperature sensitive cold morning no starts for me, and also cause random run away idle events.

This model of Jeep has no IAC, instead it has a Stepper Motor, which I have replaced.

Click to expand...

What does the stepper motor do? Move the throttle plate? The 4.0 IAC is a stepper motor valve assy.

Jeep Driver said:

You need to check your timing before anything else.

Click to expand...

The timing is controlled by the ECU on Renix and HO jeeps. Are you suggesting the timing chain may have jumped?

Jeep Driver said:

You have a switch on the TBI itself, correct?


How did you set the fuel pressure when you swapped the regulator?

Click to expand...

I thought he had the 4.0 style FPR which is not adjustable except for the automatic vacuum adjustment. But now I am not sure since some other stuff is not all the same as 87-90 Renix. I thought I saw images in stuff I posted here yesterday showing the 4.0 FPR on the 86, but his question about fuel pressure has me wondering what they did use in 86? And I did read about a WOT switch on the throttle body on earlier 2.5s but I thought that was the non Renix, carb versions. Now I am wondering if it has a TPS?

So the question now I guess is just what Renix parts did they use and not use in 1986?

Okay, I haven't been able to get around to testing the things I need too due to midterms, but I can answer some of your guys' questions.

The fuel pump is inside the gas tank.

I'm not sure if my jeep has an IAT or not.

Idle Stepper Motor (Or Idle Speed Actuator) is explained here: http://www.4wdmechanix.com/Tuning-and-Troubleshooting-the-2.5L-Jeep-TBI-Four?r=1 I Think it serves the same purpose as the IAC.

Jeep Driver, I never set the fuel pressure after I removed the TB, didn't realize I had to. My WOT switch looks like it does in the previous link, it is mounted of the throttle bracket, I haven't messed with it.

Yeah, pretty much everything you need to know about my particular Jeep is on that link, including the stuff about the different FPR. It has a picture of it but doesn't mention it; if you ctrl-f 'oe-' the picture above is it.

Not sure what specific Renix parts they used, but I am 100% sure i have a TPS, as I have changed it out.