Raven Posted June 4, 2020 Share Posted June 4, 2020 1988 MJ 2.5 with manual. One day it just stopped running. So I troubleshoot it down to the fuel pump. Bought a new fuel pump and it ran. Everything was going well and then it wouldn’t start. I can hear the fuel pump turn on when ever I turn on the ignition. I have spark and fuel but it won’t start. I decided to do a tune up. It needed one anyway. Replaced spark plugs, rotor and cap, spark plug wires, the CPS. Even after all the cranking the battery still reads 13.7 vdc. I put new grounding straps in battery to body, body to engine, battery to engine. Still won’t start. when it does try to start it just pops and backfires through the throttle body. Link to comment Share on other sites More sharing options...
224ftlb Posted June 4, 2020 Share Posted June 4, 2020 Popping through the throttle body is timing. Either you got the firing order wrong on the tuneup or the timing chain has jumped or the ecm went bad or Link to comment Share on other sites More sharing options...
eaglescout526 Posted June 4, 2020 Share Posted June 4, 2020 I strongly recommend running through some of the tests here. We boiled it down to his injector being toast but yet still Ωhms out good. Despite being an 86, 87-90 are very much similar other than the Wide Open Throttle switch moving to the P/S pressure switch. Link to comment Share on other sites More sharing options...
AMC86Kid Posted June 4, 2020 Share Posted June 4, 2020 Sounds like your timing is off if it just keeps backfiring Link to comment Share on other sites More sharing options...
Raven Posted June 4, 2020 Author Share Posted June 4, 2020 Ok today I’ll look into the timing and other things mentioned. Link to comment Share on other sites More sharing options...
gogmorgo Posted June 4, 2020 Share Posted June 4, 2020 How much fuel? Popping through the throttle body can also indicate a lean condition. I’ve had interesting things happen after changing a fuel pump, including the rubber hose from the pump failing or coming off, as well as the pump coming out of the sock at the bottom, meaning it starts pulling fuel from the middle of the tank and I would “run out” of gas with still a half-tank left. Link to comment Share on other sites More sharing options...
Raven Posted June 5, 2020 Author Share Posted June 5, 2020 As you try to start it 98% of the time it won't fire up at all. It won't even act like its going to start. It just turns over and over again doing nothing. But the few times it tried to start the engine started and then rambled and popped and backfired through the throttle body. I checked the CPS again and it ohms out correctly and the voltage it proper. I eliminated C-101, one wire at a time and second checked all wires prior to solder and heat shrink. Still not starting up. I rechecked all the spark plug gaps, the new spark plug wires to be certain they are clicking down on the spark plug and the distributor cap. We still have spark. I checked all vacuum lines and other wiring and their connectors. The battery still reads 13.5 VDC. I have not ran number one cylinder up to TDC and checked the rotor bug. I wanted to try all this first. We are getting fuel but I don't know what the new fuel pump is putting out in pressure. This came from the factory as a 2.5L with an Automatic 2x4. The PO swapped it to a manual. I'm dreading pulling the dash and checking all wires and those running down the steering column. Link to comment Share on other sites More sharing options...
Raven Posted June 5, 2020 Author Share Posted June 5, 2020 We replaced the ECU with a known good unit and it still doesn’t start. I retested the new CPS and the ohms/voltage are dead on. Ran number one cylinder to TDC and the rotor bug points to cylinder one on the distributor cap. now going to test the MAP and TPS. Link to comment Share on other sites More sharing options...
silvertwinkiehobo Posted June 5, 2020 Share Posted June 5, 2020 The symptoms sound like the wires are out of place. You didn't attempt to turn the dizzy, did you? You just put the wires on? You should get a cap diagram and verify they're in the correct firing order. IIRC, the Renix 2.5 controls are the same basic design as the 4.0, that is, the dizzy is not to be turned, but the way you made your write-up, you only put on tune-up parts, not tried to dial in any 'timing.' Link to comment Share on other sites More sharing options...
Raven Posted June 11, 2020 Author Share Posted June 11, 2020 It’s up and running now.... the cps was not making contact as the number two male child bent the pins and one or both weren’t making contact. It’s up and running. Link to comment Share on other sites More sharing options...
silvertwinkiehobo Posted June 13, 2020 Share Posted June 13, 2020 It never ceases to amaze me what can be done to keep an engine from starting; however, a kid doing something to a component is a new one on me. Link to comment Share on other sites More sharing options...
Eagle Posted June 14, 2020 Share Posted June 14, 2020 On 6/11/2020 at 2:57 AM, Raven said: It’s up and running now.... the cps was not making contact as the number two male child bent the pins and one or both weren’t making contact. It’s up and running. Pins? On a CPS? What pins? Link to comment Share on other sites More sharing options...
Raven Posted June 18, 2020 Author Share Posted June 18, 2020 There are plastic sheaths on one connector. The other has the male pins. If they aren’t lined up one of the pins will bend over the sheath and not make contact. Or so is the method this one uses Link to comment Share on other sites More sharing options...
omega_rugal Posted June 18, 2020 Share Posted June 18, 2020 how could you get fuel and spark WITHOUT the CPS? whatever.-.. Link to comment Share on other sites More sharing options...
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