railroad sam Posted March 29, 2021 Share Posted March 29, 2021 My 1987 Comanche 2.5L starts for a second then shuts down. Will do this countless times. Will not continue running. I have 15 psi fuel pressure. Have replaced filter. Also getting fuel to throttle body. Have cleaned crankcase position sensor. Ran great then this problem occurred. Any suggestions. I'm not a mechanic. Can do a little. Had this truck since new. Thanks, Railroad Sam Link to comment Share on other sites More sharing options...
eaglescout526 Posted March 29, 2021 Share Posted March 29, 2021 Are you sure you’re getting fuel after the start up sequence? I only ask because the fuel pump relay is bypassed for the priming sequence. Link to comment Share on other sites More sharing options...
89 MJ Posted March 29, 2021 Share Posted March 29, 2021 If you know that you are getting fuel, I'd check to make sure that you are getting spark. It sounds like the timing could be off too. Link to comment Share on other sites More sharing options...
ghetdjc320 Posted March 30, 2021 Share Posted March 30, 2021 39 minutes ago, eaglescout526 said: Are you sure you’re getting fuel after the start up sequence? I only ask because the fuel pump relay is bypassed for the priming sequence. Sounds like it has power on crank but not run. Does it sound like it just sputters out? Link to comment Share on other sites More sharing options...
railroad sam Posted March 30, 2021 Author Share Posted March 30, 2021 Thanks for reaching out with help. Yes I've disconnected both fuel lines one at a time to throttle body. Turn key to on and I'm getting fuel. Even dropped fuel line at filter. Turn key and getting fuel. Spliced in fuel pressure gauge at filter area. Get 15 psi right on spec. Thanks, Railroad Sam Link to comment Share on other sites More sharing options...
railroad sam Posted March 30, 2021 Author Share Posted March 30, 2021 Truck will start for about a second or two then dies. Saw a video. Showed disconnecting battery and reconnecting might reset ECU. Link to comment Share on other sites More sharing options...
eaglescout526 Posted March 30, 2021 Share Posted March 30, 2021 I would put money on a bad fuel pump relay. The Renix system bypasses that relay to prime the fuel rail and once you going into crank position, the system switches the fuel pump power to the relay. So you could be getting fuel every where just from the priming but not for the engine to run. Link to comment Share on other sites More sharing options...
railroad sam Posted March 30, 2021 Author Share Posted March 30, 2021 Wow. That is something I will look into. I did notice also with fuel pressure gauge attached that immediately after turning ignition to off my 15 psi would went to zero psi quick. I will look for that relay and replace it. Thanks so much, Railroad Sam Link to comment Share on other sites More sharing options...
railroad sam Posted March 30, 2021 Author Share Posted March 30, 2021 Thanks for all the help to those who answered. Will replace fuel pump relay a d let all know if we are up and running. Railroad Sam. Link to comment Share on other sites More sharing options...
87MJTIM Posted March 30, 2021 Share Posted March 30, 2021 Does the 2.5 have an IAC? I had the same problem with my 4.0 in my CJ. It would start up but died once I let off the gas. I took the old IAC out and cleaned it (ended up replacing it). It runs fine afterwards. (Mine is a 93 4.0 HO. ) Link to comment Share on other sites More sharing options...
eaglescout526 Posted March 30, 2021 Share Posted March 30, 2021 1 hour ago, 87MJTIM said: Does the 2.5 have an IAC? I had the same problem with my 4.0 in my CJ. It would start up but died once I let off the gas. I took the old IAC out and cleaned it (ended up replacing it). It runs fine afterwards. (Mine is a 93 4.0 HO. ) No, us Renix 2.5L’s have the ISA motor. Similar to the IAC but bigger and on the front of the TB Link to comment Share on other sites More sharing options...
railroad sam Posted March 30, 2021 Author Share Posted March 30, 2021 Well Men I replaced the fuel pump relay this morning. Fired right up. Got it home. Restarted and ran. Later went to start it. Doing the same thing. Starts for a second and dies. Cleaned the solenoid connections as well. Retried starting same thing. Thanks for everyone's input. Railroad Sam 1987 Jeep Comanche 2.5L 4WD Metric Ton Package. Original owner Link to comment Share on other sites More sharing options...
eaglescout526 Posted March 30, 2021 Share Posted March 30, 2021 So for a quick minute it ran and drove just fine? But now it’s doing it again? @Ωhmis it possible for something to kill a relay like this? Link to comment Share on other sites More sharing options...
Ωhm Posted March 30, 2021 Share Posted March 30, 2021 37 minutes ago, eaglescout526 said: is it possible for something to kill a relay like this? BORG cube relays are pretty tough, but can also be the problem. Remove FP relay from its relay block and jumper PIN_1 to PIN_4. Does vehicle START and RUN? Link to comment Share on other sites More sharing options...
eaglescout526 Posted March 30, 2021 Share Posted March 30, 2021 1 minute ago, Ωhm said: BORG Assimilate. Link to comment Share on other sites More sharing options...
jdog Posted March 30, 2021 Share Posted March 30, 2021 I don't have the manual in front of me but I r would be checking power and ground at the relay, then checking to make sure the PCM is grounding the relay Link to comment Share on other sites More sharing options...
Ωhm Posted March 30, 2021 Share Posted March 30, 2021 1 minute ago, jdog said: I don't have the manual in front of me but I r would be checking power and ground at the relay, then checking to make sure the PCM is grounding the relay If it RUNs with the jumper, that's next step. Link to comment Share on other sites More sharing options...
Jesse J Posted March 30, 2021 Share Posted March 30, 2021 20 hours ago, railroad sam said: Had this truck since new. are you an original owner? Link to comment Share on other sites More sharing options...
railroad sam Posted March 31, 2021 Author Share Posted March 31, 2021 Proud owner since new. Yes Link to comment Share on other sites More sharing options...
cruiser54 Posted March 31, 2021 Share Posted March 31, 2021 Sam, have you ever visited my website and completed Tips 1 through 5? Link to comment Share on other sites More sharing options...
railroad sam Posted April 1, 2021 Author Share Posted April 1, 2021 Thanks. I will try that. Have read your tips in the past. Not familiar with Tips 1 thru 5. Also not not good with a multimeter. Will give it a try. Out of town working right. Thanks, Railroad Sam Link to comment Share on other sites More sharing options...
cruiser54 Posted April 1, 2021 Share Posted April 1, 2021 Reading doesn't do any good. You must complete them. Leap of faith is all you need. Please do them before throwing any more time and money at your Jeep. Need a meter tutorial? I have one somewhere that I could link you to. Link to comment Share on other sites More sharing options...
railroad sam Posted September 3, 2021 Author Share Posted September 3, 2021 Hello y'all, Been working on my 87 Jeep Comanche again. The problem was will crank and want start. Pour gas in throttle body and it will start until gas is gone. Since I've replaced the starter relay, new fuel pump and filter, crankcase position sensor and I even put a kit in throttle body with new fuel pressure regulator. Still no start. I've disconnected fuel lines and hit start. Gas goes every where. Fuel pump pressure is on spec of 15 psi. After rebuilding and cleaning throttle body I was hoping it would start. Big no. Doing same thing. Cranks and no start. Pour gas in throttle body and will start until gas is gone. I did some of cruising 54s suggestions. Cleaning fuel pump ground, block to firewall ground. Opened and cleaned c101 connector. I don't get what causing truck not to start. I'm no count with a multimeter. No clue how to use one. Wondering if my injector or ECM could be bad. Any suggestions would be appreciated. Thanks for your help. Railroad Sam Link to comment Share on other sites More sharing options...
eaglescout526 Posted September 3, 2021 Share Posted September 3, 2021 Go rent a injector noid tester and plug it into the injector plug. See if you get a light or not. Should be dim(or bight, one of the two) and pulsing. If it does then the ECU is good. If nothing then it’s bad. But the injector and ECU are close in price these days so I’m willing to bet it’s the injector. Rarely they go bad but there is a 25 page epic on how we came to the conclusion that the injector was bad despite testing within ohm’d specs. Link to comment Share on other sites More sharing options...
railroad sam Posted September 3, 2021 Author Share Posted September 3, 2021 Cruiser54, I want to thank you for all your advice. Also the hard work you put into on your tips page. Thanks again. I have since new a 87 Jeep Comanche. 2.5l. Truck was running great. Went to visit granddaughter a mile away jeep wouldn't start. Someone suggested replacing fuel starter relay. I disconnected battery. Put in new starter relay. Fired right up and got truck back home. It also restarted. Later in the day. Tried to start it. Starts, runs a second and dies. Well I tested fuel pump 15 psi. Good. New fuel filter installed. Pour gas in throttle body it will start. This was in March 2021. Now In August. I replace crankcase position sensor. I had had trouble like this before and the CPS was the culprit. Well I went ahead replace fuel pump. Put in throttle body kit. Including new fuel pressure regulator. I've cleaned the fuel pump ground, dipstick grounds, coil contacts, block to firewall ground, opened c101 up and cleaned it. Didn't splice it though. Surely after the throttle body kit it would start. Because when I disconnect fuel line and hit start gas is being pumped up to throttle body. So I thought it had to be fuel pressure regulator. Nope. Still won't start. Pour gas in throttle body and it will start. Like I've said I own a old Greenlee multimeter but have no clue as how to use it. Watched some YouTube on it. Didn't really help my specific model the man tested it's capacities until he fried it with great delight. Anyway thanks again for all you do, Railroad Sam Link to comment Share on other sites More sharing options...
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