2.5L Crank, no start

[GonzoTheGreat]

I have an '89 2.5L TBI, auto tranny, 2WD Comanche

 

After being parked for quite some time, the engine cranks over no problem, but it will not fire. I have watched the fuel pulsing from the injector. I have seen spark at each cylinder. I checked every sensor that I have that corresponds with this site. All values were within the specs listed there (except the TPS which I believe is different for four cylinders. There, I have just under 5v signal at closed, and if I recall it was just under 2v at WOT, which I believe is ok, but I also don't think I'd get a crank, no-start from a problem here). The only sensor related thing I wasn't sure about was the O2 sensor. I have .7ohms across the heater wire, but I don't know how to test it otherwise. I have an REM, and it's reading 0.02-0.04v on the O2 and air/fuel is 13.4. I don't recall what it read while starting when everything worked, so I don't know if these values are good, but I also don't believe that would prevent the engine from firing at all, if there were a problem.

 

I've tried splashing fresh gas down the throttle, thinking maybe the tank fuel is old, but I didn't even get a sputter. Ether also did not cause it to fire, but after I aired out the manifold and unplugged the injector, I could get a little cough with ether, but no proper firing. I know very little about these injectors, but from what I've read in various threads on here, the injector seems to be doing what it's supposed to, and not doing anything it isn't supposed to. I would like to check fuel pressure, but I don't have a way to do that at the moment. It sprays out pretty strong when I disconnect a line though.

 

My only remaining thought is that the spark is too weak. I checked spark by holding the plugs to the block, and it was there each time, but it didn't really fry my hand through the boot like I've felt in the past. I know that's not a good metric, but I'm running out of things to check. I'm trying to track down new plugs/wires/cap/rotor/coil just to rule that out, although none of them are more than 2 years old. It is however extremely hot and humid where the truck was stored and there was a little corrosion on one contact in the dizzy cap, which I've now cleaned up, and the coil has some surface rust.

 

The engine cranks strong, but for the life of me I can hardly get it to cough just a little, let alone fire on all cylinders. I have to put down the tools and do some head scratching now, so if anyone has any input, there's probably something obvious I'm neglecting, and I'd love for anyone to point that out.

 

TLDR: Air/fuel/spark-ok. No bang-bang.

[Ωhm]

1 hour ago, GonzoTheGreat said:

I have .7ohms across the heater wire

 

Is that 0.7Ω or 7Ω's across your O2S Heater? What are your STFT and LTFT values with KEY ON?

[eaglescout526]

How’s the contacts for the coil at the ICM? Those literally stopped my XJ dead in its tracks while driving one day. 

[GonzoTheGreat]

49 minutes ago, Ωhm said:

 

Is that 0.7Ω or 7Ω's across your O2S Heater? What are your STFT and LTFT values with KEY ON?

 

I saw a lot of numbers today. It might have been 7 or .7 with my meter on the wrong scale. I'll double check that in the morning. ST and LT are both 128

 

42 minutes ago, eaglescout526 said:

How’s the contacts for the coil at the ICM? Those literally stopped my XJ dead in its tracks while driving one day. 

 

squeaky clean. Both the pins on the bottom of the coil, and the connectors to the ICM. I had cleaned and greased them with dielectric in the past, and it looks like it held up. Good springiness on the ICM contacts as well.

 

I've cleaned every connector within the last 2 years, and done all the cruiser tips btw. Forgot to mention that in the first post. I've added new grounds where recommended, including replacing the ribbon to the firewall with a new cable, extra fuel pump ground, clean ground behind tail light, etc.

[pizzaman09]

Does it sound like it is making good compression or does it sound like it's cranking too fast? 

 

My only other thought is for some reason is the ignition timing off?  Do you own a timing light?  Are the plug wires in the right order from the distributor?

[GonzoTheGreat]

35 minutes ago, pizzaman09 said:

Does it sound like it is making good compression or does it sound like it's cranking too fast? 

 

My only other thought is for some reason is the ignition timing off?  Do you own a timing light?  Are the plug wires in the right order from the distributor?

Yeah, It cranks over like normal. The only thing I did was park it. It ran fine when parked. I can’t imagine it would lose compression or timing from just sitting, but I’m trying to track down a compression tester just in case. I’m quite a ways from home, and a bit limited on tools, but where there’s a will there’s a way.
 

And again, I don’t see how timing would change from just sitting, but if there was a problem with that, it could explain why I have fuel and spark, but no combustion. I put a new coil/plugs/wires/and rotor in today. New cap arrives Monday. Still no change, and yes both the old and new wires were installed correctly. I don’t have a timing light with me, but I may be able to borrow one. I just don’t know how it could have changed at all from just sitting parked. 

 

On 4/11/2025 at 6:31 PM, Ωhm said:

 

Is that 0.7Ω or 7Ω's across your O2S Heater?

And that’s a solid 7.1 ohms on the connector pins. 

[eaglescout526]

On 4/11/2025 at 3:47 PM, GonzoTheGreat said:

and if I recall it was just under 2v at WOT, which I believe is ok, but I also don't think I'd get a crank, no-start from a problem here)

 

Needs to be 4.6V. Either between 4.62V or 4.65V at WOT. Under 2V is not right.

[GonzoTheGreat]

16 hours ago, eaglescout526 said:

 

Needs to be 4.6V. Either between 4.62V or 4.65V at WOT. Under 2V is not right.

My bad. I had my values reversed. I checked again and it’s 4.7V at WOT and around 1V closed. I think it would settle to the correct .8v if the ISA were retracted. Again though, I don’t think this would be a crank, no-start if it were just a little off. As I understand it, you can even run the engine with the TPS unplugged, it just doesn’t run well. 
 

I'm wondering if either the ICM or ECU is screwing up the timing advance. I am still trying to find a timing light I can borrow, but I did check the rotor at TDC cyl1, and it’s just past the cyl1 pickup in the cap, which I understand to be the correct location, then 3,4,2 to follow.

[eaglescout526]

35 minutes ago, GonzoTheGreat said:

I understand it, you can even run the engine with the TPS unplugged, it just doesn’t run well. 

Yup! Runs ok until you go to rev it. Then it’ll just want to die. 
 

[GonzoTheGreat]

On 4/13/2025 at 4:01 PM, eaglescout526 said:

Yup! Runs ok until you go to rev it. Then it’ll just want to die. 
 

Ok that’s something to note on a running engine, but it doesn’t really help with a no-start condition. 
 

I’m starting to go a little crazy here. I’ve rechecked and recleaned my engine-chassis-battery grounds. I’ve rechecked every sensor, and they’re all giving proper resistances and voltages. I’ve rechecked for fuel and spark, and it’s there. I’m still trying to find a timing light and pressure gauge just to be 100% sure I have the right amount of each. Hopefully that will happen tomorrow. Stuff is a little tricky to find here. 🇨🇷
 

I have now swapped in a known-good, oem ICM and coil, and a known-good, oem ECU.

 

the only part of the ignition system I haven’t been able to find locally is the distributor cap. It’s pretty new, so there’s not much to go bad there, but I checked it anyway. I get about 30ohms between the center post on the outside and the spring-loaded contact on the inside. I didn’t expect to find any resistance there. Can someone with a good dizzy cap check that number? If I push the spring down all the way with the meter probe, it drops to about 3ohms. 

[pizzaman09]

I haven't measured it but 30 ohms makes sense for that connection.  Also 30 ohms is plenty low enough to pass the 30k+ volts that an ignition system runs at.

[GonzoTheGreat]

Thanks @pizzaman09!

 

Ok. So, problem solved. This was not a Comanche specific problem, or anything renix, or even electrical. Just basic mechanics. Compression passed the thumb-on-the-spark-plug-hole test, but leaving it parked for 11 months allowed the rings to dry out, and it wouldn’t hold enough compression for combustion. With enough jumping, cranking, and feathering the throttle, it came back to life. Good to know all my electrical testing was accurate at least 
 

I’ll add a little more detail in my road trip thread (which fortunately, is back on track). But long story short I met a super cool Costa Rican dude with all the renix parts and knowledge you could ask for. It was good to talk through the situation with a knowledgeable person, even despite a language barrier. 

[pizzaman09]

53 minutes ago, GonzoTheGreat said:

Thanks @pizzaman09!

 

Ok. So, problem solved. This was not a Comanche specific problem, or anything renix, or even electrical. Just basic mechanics. Compression passed the thumb-on-the-spark-plug-hole test, but leaving it parked for 11 months allowed the rings to dry out, and it wouldn’t hold enough compression for combustion. With enough jumping, cranking, and feathering the throttle, it came back to life. Good to know all my electrical testing was accurate at least 
 

I’ll add a little more detail in my road trip thread (which fortunately, is back on track). But long story short I met a super cool Costa Rican dude with all the renix parts and knowledge you could ask for. It was good to talk through the situation with a knowledgeable person, even despite a language barrier. 

That's awesome!  I was skeptical of compression.  Engines that sit for a while can have issues like that.  A trick to getting an engine running with stuck rings is to throw a little oil or PB blaster or WD40 down the cylinder to help the rings seal enough to build some compression.