Help!

[Jackh37097]

I recently purchased an ‘89 jeep Comanche sport truck with the 4.0 l motor with the 5 speed gear box and 4wd. The Jeep has sat up supposedly untouched since 2005 according to previous owner. Since buying it we dropped the fuel tank and we’re using a temporary gas can with a new fuel pump and lines. We took off the fuel rail and cleaned it. We checked all injectors and cleaned them out and put it all back on the truck. We check for spark and checked all plugs and it is getting enough spark for the engine to start. We checked compression on all cylinders and are getting around 130-150 on all cylinders except the back one which is getting around 90, albeit low, but not low enough to stop from running. We of course cleaned out the air box and stuck a new filter into it. At about this point of cleaning and checking and making sure, we try to start the vehicle and it successfully ran for a few seconds and shut off due to the brake clean sprayed into the holes while the fuel injectors were out. For the life of us, we can not get it to start. We have gone through and done all the checks previously stated and have accomplished nothing. We inspected closer and found the crank sensor was damaged and replaced it with a brand new one that we tested and installed, but still we get nothing. If you have run into a similar issue or have a lot of knowledge on these Comanches, please write back. I can provide pictures and additional info, but a point in any direction would be greatly appreciated. 

[ghetdjc320]

Have you checked your fuel pressure? If so, what are you getting at the fuel rail?

[scaleless]

If it ran on brakleen, it's definitely fuel.  Run down to the parts store and rent a fuel pressure guage.  Grab a new fuel filter while you're at it.  That said, it might run with one cylinder down so much on compression, but probably not too well.  Could also be an indication of more serious issues, and I would bet is the reason why it was parked.

[JMO413]

2 hours ago, ghetdjc320 said:

Have you checked your fuel pressure? If so, what are you getting at the fuel rail?

This is the first place to start. IMHO

[Jackh37097]

4 hours ago, ghetdjc320 said:

Have you checked your fuel pressure? If so, what are you getting at the fuel rail?

I’m getting 40 psi at the rail with pressure regulator unplugged, but it drops fuel pressure right as it’s about to start 

 

[Jackh37097]

2 hours ago, JMO413 said:

This is the first place to start. IMHO

I’m getting 40 psi at the rail with the regulator unplugged

[Jackh37097]

2 hours ago, scaleless said:

If it ran on brakleen, it's definitely fuel.  Run down to the parts store and rent a fuel pressure guage.  Grab a new fuel filter while you're at it.  That said, it might run with one cylinder down so much on compression, but probably not too well.  Could also be an indication of more serious issues, and I would bet is the reason why it was parked.

We tried checking if it would run on brake clean again after it initially ran for a few seconds and got nothing from it 

[JMO413]

http://cruiser54.com/?p=50

 

Test the CPS now that it's installed. Would be my next step.

[JMO413]

Filling out your signature will help everyone know what your working on.

 

 

[JMO413]

The 88 electrical manual is on this link. It's a great thing to have. 

 

 

[Jackh37097]

31 minutes ago, JMO413 said:

http://cruiser54.com/?p=50

 

Test the CPS now that it's installed. Would be my next step.

Tested it before we put it on, it’s known good

[JMO413]

19 minutes ago, Jackh37097 said:

Tested it before we put it on, it’s known good

Read the link from cruiser on how to test it. The only real test is installed and testing for volts AC.

[Jackh37097]

13 minutes ago, JMO413 said:

Read the link from cruiser on how to test it. The only real test is installed and testing for volts AC.

I will do that, thanks for the advice!

[JMO413]

The hose from the throttle body to the MAP sensor likes to fall off if you look at it wrong. Double check it's hooked up and not cracked. Your welcome. 

[JMO413]

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm#:~:text=RENIX vehicles use a SEPARATE,(See bottom of page.)

 

This sight is also amazing. Sensor locations and test procedure and values.

 

[ghetdjc320]

So, safe to say injectors aren’t firing. Doesn’t the injector firing rely on the cam signal in the dizzy or is renix different. 

[scaleless]

3 hours ago, ghetdjc320 said:

So, safe to say injectors aren’t firing. Doesn’t the injector firing rely on the cam signal in the dizzy or is renix different. 

Yes, however the computer is pretty good at guessing the injector timing if the distributor ring burns up.  Probably wouldn't cause a non-start, but anything is possible.

[Jackh37097]

On 6/27/2021 at 6:26 PM, JMO413 said:

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm#:~:text=RENIX vehicles use a SEPARATE,(See bottom of page.)

 

This sight is also amazing. Sensor locations and test procedure and values.

 

I am back with good and bad news. We tested the CPS and it's good. We fixed some wiring on the injectors and have injector pulse while cranking, we threw in a new ignition coil and have good spark, we have good enough compression to run and we have air. We are able to run it on brake fluid, but we found that we have no injector pulse at all once it starts running off of the brake clean. I'm thinking maybe it's the ECU at this point but we really aren't sure. Have you heard of any similar problems before and possible solutions? thanks again for the point in the right direction, we are closer now! I can feel it!

[Ωhm]

1 hour ago, Jackh37097 said:

We are able to run it on brake fluid, but we found that we have no injector pulse at all once it starts running off of the brake clean.

 

Check your Fuel Pump Relay. Swap it out with one of the others or jumper Pin_1 to Pin_4 with relay removed. Check your fusible links at starter relay.

 

 

[JMO413]

Have you bypassed the ballast resistor yet? 

 

[scaleless]

I would listen for the fuel pump when the key is on.  It's fairly loud if it's working.  You can also get a rough idea of fuel pressure by depressing the Schrader valve on the fuel rail and seeing how forcefully it vents.

[Jackh37097]

9 hours ago, JMO413 said:

Have you bypassed the ballast resistor yet? 

 

Yeah we have the fuel pump wired to 12v with a switch, we use the switch whenever we crank it

[Jackh37097]

10 hours ago, Ωhm said:

 

Check your Fuel Pump Relay. Swap it out with one of the others or jumper Pin_1 to Pin_4 with relay removed. Check your fusible links at starter relay.

 

 

We replaced it with a brand new relay, but we will definitely try to jump it! We were headed in this direction yesterday before we stopped working on it so this sounds good

[gvthnks]

Just went through something similar with an 87 that had sat for 11 years.  Be sure your injector wires are hooked up to the correct injectors.  On mine there was enough room for there to be confusion. 

If it'll run on starting fluid, it's a fuel issue.  On mine, I ended up with the head off and engine out to replace all the freeze plugs and lifters but the injectors were so fouled with gunk on the bottom where the fuel was supposed to come out, that even if they were firing correctly, it wouldn't have been good. 

 

Like others have stated, check that map hose not just where it plugs into the map sensor, but also where it plugs into the throttle body.  Mine was sucking air there too causing issues.  Check all the other vacuum ports too and make sure the EGR valve isn't stuck open.  Crack the throttle just a hint when you're cranking.  I've seen the idle air control valve so badly dirty that it wasn't letting anything through and the engine can't run without air.  Cracking the throttle will bypass the IAC and allow enough air in to let it start and run.  Clean the IAC and throttle body when you can.  Nothing will work correctly if the TB unit is very dirty.  As a matter of course, I clean the IAC and throttle body on every one of these engines I work on, cause they're all dirty.  Then you've alleviated that as a possible issue and I guarantee you it needs it anyway. 

Mine would run on 4 cylinders when I first started trying to get it going, but I had to crack the throttle some to get it to crank.  That told me the IAC was dirty or non-functional.  Easy fix. 

 

Lastly, don't fret.  If it ran before, it'll run again.  Go over Cruiser54's list and read through all the comments on his page.  There's more knowledge there that's renix specific than anywhere else I've found.  I've had probably 15 of these 6 cylinders over the years but avoided the renix versions.  After reading some theory about how it works and the common failure issues, it isn't so bad.    The info here has helped me tremendously getting mine resurrected.  It's not on the road yet, but we're getting close. 

[75sv1]

Sort of a simular issue on a 2000 XJ. I replaced fuel pump and all sensor except O2. Also, had a spare coil pack for it. I put a Noid light on the first or #1 Injector. Cranked, and cranked, no light came on till I let the key off. Then the Noid light pulsed. A friend at work said it might be the ignition switch on the steering column. I replaced it with a NAPA Echlin one. Took a few tires and some starter fluid. Then it ran, then ran some more, then ran on fist turn of the key. I also replaced the injectors with 12 hole ones.