onlyinajeep726 Posted February 18, 2013 Share Posted February 18, 2013 I have an '86 Comanche 2.5L with Throttle Body Injection and a AX4, 4-speed manual. The engine is not the original Comanche engine, but one from a YJ Wrangler from what I would assume is similar in year and function. Anyway, I was driving it the day before last to work and it was doing fine until it warmed up. All of a sudden, it just acted like it wasn't getting gas when I pressed the accelerator. It idled back down and was running rough, but as soon as I tried to give it gas, it would spit/sputter and bog down. It shut off on its own, so I gave it a few seconds and then I started it back up and the problem went away, for a little while anyway. I got about 2 miles further down the road and then the same thing. That time, I cut the engine off and restarted it about 10 seconds later. I made it all the way to work from then on without hesitation. On the way home from work, the same thing happened 3 more times. Anyone have any ideas on what this could be caused by? It has new spark plugs, a clean air filter, fuel injector cleaner and Iso-heet (water remover) in the gas. Edit... I took it for a test drive today with my dad to see what he thinks, and it did it about 4 times just going a couple miles down the street. We both feel as though it something fuel related or sensors starving it of gas. I have noticed a pattern, however. When it begins these spells of bogging down, I will turn of the engine and start it again while I'm coasting (did that all 4 times during today's drive). Once it's been restarted, it runs and drives perfectly fine for a little while until the issue arises again. It's the damndest thing because I don't have a clue how to begin sourcing the problem... I imagine just strictly looking at the fuel system, there are really only four main components: Fuel pump, fuel filter, pressure regulator and TB injector. The FP seems to prime fine and I can hear it running when idled and what not, though I haven't tested it for the 14-15 psi pressure that's needed. The fuel filter looks to have been recently replaced by the previous owner as it appears new from the outside. The TB injector seems to be spraying good and in a conical fashion. I haven't put a vacuum meter on the regulator, but that's next. Also, it's been suggested on CherokeeForum that it could be my TPS. I will be checking that with my digital multimeter. The O2 sensor appears to have been replaced by the PO. So, as far as sensors go, I don't know what else could alter the A/F ratio. I guess the most confusing part of it all is that when I cut it off and restart the engine, it runs fine for a little while. It's very random when the symptom occurs. Anyway, sorry for the long post, but I really need to figure it out soon because I'm about to stop driving my XJ to swap in a stroker. Any help or advice on this MJ issue would be greatly appreciated. Forgot to mention, the PO removed the cat and just ran a pipe to the muffler, so a clogged cat can't be an issue. Sorry if speaking of this is against forum rules, I am simply mentioning it to eliminate that as a potential issue... Link to comment Share on other sites More sharing options...
Comanchemodder Posted February 18, 2013 Share Posted February 18, 2013 You checked the O2 sensor. Did you check the MAP sensor voltage? I found the following link very helpful in learning and diagnosing problems with the 2.5l: http://www.4wdmechanix.com/Tuning-and-Troubleshooting-the-2.5L-Jeep-TBI-Four.html Link to comment Share on other sites More sharing options...
onlyinajeep726 Posted February 18, 2013 Author Share Posted February 18, 2013 Thank you for the response and the link. I will be reading over it thoroughly after work and see what all I can derive from it. I hope it's something simple; of course, don't we all? haha. Link to comment Share on other sites More sharing options...
Eagle Posted February 19, 2013 Share Posted February 19, 2013 I imagine just strictly looking at the fuel system, there are really only four main components: Fuel pump, fuel filter, pressure regulator and TB injector. The FP seems to prime fine and I can hear it running when idled and what not, though I haven't tested it for the 14-15 psi pressure that's needed. The fuel filter looks to have been recently replaced by the previous owner as it appears new from the outside. The TB injector seems to be spraying good and in a conical fashion. I haven't put a vacuum meter on the regulator, but that's next. Sounds to me like a CPS issue. The 2.5L TBI system is a Renix system, and it uses the same CPS as the Renix 4.0L. Link to comment Share on other sites More sharing options...
onlyinajeep726 Posted February 19, 2013 Author Share Posted February 19, 2013 Sounds to me like a CPS issue. The 2.5L TBI system is a Renix system, and it uses the same CPS as the Renix 4.0L. Does it matter if I pull a CPS off of an '89 4.0L with an automatic tranny? Link to comment Share on other sites More sharing options...
cruiser54 Posted February 19, 2013 Share Posted February 19, 2013 Does it matter if I pull a CPS off of an '89 4.0L with an automatic tranny? No. But why not test your. Ever read this?Renix CPS Testing and Adjusting Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark. Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad. The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark. Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected. You should get a reading of .5 AC volts. If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer. Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off. A little trick for increasing the output of your CPS is to drill out the upper mounting hole to 3/8” from the stock 5/16”, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts. Revised 01-26-2013 Link to comment Share on other sites More sharing options...
onlyinajeep726 Posted February 19, 2013 Author Share Posted February 19, 2013 Yes lol. I actually went through your entire Renix Tips list last night. I plan on testing it and looking for any crude that may have built up on it. I will also check the TPS and MAP... probably everything while I'm at it. Link to comment Share on other sites More sharing options...
onlyinajeep726 Posted February 23, 2013 Author Share Posted February 23, 2013 So, I spent part of the day and some of tonight to diagnose the issues I've been having from this 4-banger... Needless to say, no luck as I am back here for suggestions. What I've done so far: - Swapped the TPS to a brand new one - Removed, cleaned and reinstalled the CPS on the transmission. (Was dirty as hell, just like Cruiser suggested) - Replaced the MAP sensor - Replaced a couple vacuum hoses that were torn Also, I found that the WOT switch was plugged into the CTS on the intake manifold and the harness end of both plugs were plugged into one another, if that makes any sense at all. Evidently, when the original owner had the YJ engine swapped in, they hooked those up wrong. Anyway, now the thing is worse off than it was before... seemed to be fine when I done these things (idled fine in the garage), but the moment I took her out on the road, it ran even worse and I have no idea where to go with it next. Any help will be highly appreciated. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 23, 2013 Share Posted February 23, 2013 Wonder what kind of fuel pressure you have. Link to comment Share on other sites More sharing options...
johnr Posted February 23, 2013 Share Posted February 23, 2013 complete shot in the dark. i had fuel pressure problem. it was only putting out 12 psi. ok no problem its the fuel pump. bought one, took down the tank (just because) pulled out the sending unit to find that the short piece of rubber fuel line that ran from the pump to the hard line on the out side was almost completely disintagrated and was more like a sprinkler than a hose . i replaced the hose & the pump problem solved. to check the fuel line pressuer i put a gauge inline just in front of the filter. i can't remember if i could not find the shrader valve or i just did not have one but anyhow i hooked it up statred the truck and it was pretty obvious that there was low pressure. Link to comment Share on other sites More sharing options...
onlyinajeep726 Posted February 23, 2013 Author Share Posted February 23, 2013 Wonder what kind of fuel pressure you have. I was thinking about it last night after I made my previous post, and thought more on the subject. I will see if I can test it for correct pressure. I guess the reason I haven't focused on the FP more is because it idles fine and will take off fine, but then randomly, after I get up to speed, the Jeep just goes nuts (and it doesn't always do it right away or sometimes not at all). Question for you... if it tests fine in idle, is there a way I can test it safely on the side of the road if it starts bogging down and sputtering? I guess what I'm saying is that I assume you have to hook up the fuel pressure meter while the ignition is off so I guess there's no way to do that with the engine running, IE. I can't exactly see if it's the fuel pressure when it begins its spells of erratic running. Either way, I will start doing a round of tests and get back to you. Thank you for your help so far. Link to comment Share on other sites More sharing options...
onlyinajeep726 Posted February 23, 2013 Author Share Posted February 23, 2013 complete shot in the dark. i had fuel pressure problem. it was only putting out 12 psi. ok no problem its the fuel pump. bought one, took down the tank (just because) pulled out the sending unit to find that the short piece of rubber fuel line that ran from the pump to the hard line on the out side was almost completely disintagrated and was more like a sprinkler than a hose . i replaced the hose & the pump problem solved. to check the fuel line pressuer i put a gauge inline just in front of the filter. i can't remember if i could not find the shrader valve or i just did not have one but anyhow i hooked it up statred the truck and it was pretty obvious that there was low pressure. I just saw this post after I made my last one. I didn't think about an inline fuel pressure gauge, but that's a good idea. I could just leave it there and take it for a drive, thus being able to see pressure readings when it starts wigging out. Link to comment Share on other sites More sharing options...
onlyinajeep726 Posted March 4, 2013 Author Share Posted March 4, 2013 Ok, haven't been able to work on the MJ since I've been tied up swap in a stroker into my XJ... Anyway, I started the MJ yesterday to move it and while I was at it, I just decided to do a little snooping under the hood. I swapped the two relays on the passenger side, the one that controls the fuel pump and whatever the other one is. Both looked original and were corroded. Thought I was on to something but was disappointed as expected. However, while tinkering under the hood I found another pattern when the engine decides to die. If I push on the TPS lever and let off, and do that repeatedly, as though I was pushing the accelerator but without giving it gas, it will idle fine for anywhere from 30-60 seconds and then begin to slowly lose RPM's, then surge, then bog down again. It goes through this roller coaster of varying RPM's for about 20-30 seconds until it finally cuts off. Then, like I stated before in a previous post, I can restart the engine and it idles fine until the next round. I haven't been able to check fuel pressure coming from the pump and after the regulator, so that could still be it, I just don't know yet. Do these symptoms ring any bells for anyone? Link to comment Share on other sites More sharing options...
Egm89 Posted June 11, 2013 Share Posted June 11, 2013 I currently have the same symptoms on my 86 mj, I already changed the fuel pump, fuel filter, did a full tune up, yet no progress. Changing the tbi next, lucky enough to find one in the JY for 75 bucks. Link to comment Share on other sites More sharing options...
randomguy310 Posted June 12, 2013 Share Posted June 12, 2013 I had an 86 2.5 and was doing the same thing and the intake had came loose.. may not be your problem but doesn't hurt to make sure the intake bolts are tight Link to comment Share on other sites More sharing options...
cruiser54 Posted June 12, 2013 Share Posted June 12, 2013 I had an 86 2.5 and was doing the same thing and the intake had came loose.. may not be your problem but doesn't hurt to make sure the intake bolts are tight NEVER a bad idea to check those bolts. Link to comment Share on other sites More sharing options...
onlyinajeep726 Posted June 12, 2013 Author Share Posted June 12, 2013 I did the top ones already, but need to check the bottom ones. Link to comment Share on other sites More sharing options...
onlyinajeep726 Posted June 12, 2013 Author Share Posted June 12, 2013 Think I may have solved my own conundrum. Read... http://comancheclub.com/topic/39042-could-this-be-my-issue/?p=393332 Link to comment Share on other sites More sharing options...
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