Zadouw Posted February 19, 2023 Share Posted February 19, 2023 First time post, I have scoured most of the site and tried anything related I could find. 1989 mj, 4.0, 4wd, automatic. I got the rig recently as a project swap from a random car lot. They were able to get it to run momentarily using ether to show that the engine its self was in decent shape. 👌. Now that I have it home it will fire up perfectly fine, but then immediately shut its self off like the key was turned off. Things I have done so far: Replaced distributor cap and rotor. Replaced all plugs and wires (verified gap on new plugs). Replaced/repaired any vacuum hoses I could find. Replaced crank position sensor. Replaced fuel filter. Verified power to the fuel pump. Verified 40 psi in fuel rail. Jumped the balast resistor. I even tried starting it with the pump wired straight to power constant (via the relay and at the resistor out). I am at a loss for what could be preventing it from staying running at this point. I can't seem to check any codes as the "maintenance" light does not illuminate (swapped in a known good bulb). Any advice, or ideas would be greatly appreciated. Thanks in advance! Link to comment Share on other sites More sharing options...
Ωhm Posted February 19, 2023 Share Posted February 19, 2023 Using a voltmeter or 12vdc testlight (preferred) check for Battery_Voltage_(B+) on the following pins (use battery_negative terminal for ground): D1_5: B+ (Hot at all times) D1_6: At KEY ON only (B+ (Hot for 2-3 seconds)). D2_4: B+ (Hot during KEY ON and Hot during CRANK). Link to comment Share on other sites More sharing options...
Zadouw Posted February 19, 2023 Author Share Posted February 19, 2023 12 minutes ago, Ωhm said: Using a voltmeter or 12vdc testlight (preferred) check for Battery_Voltage_(B+) on the following pins (use battery_negative terminal for ground): D1_5: B+ (Hot at all times) D1_6: At KEY ON only (B+ (Hot for 2-3 seconds)). D2_4: B+ (Hot during KEY ON and Hot during CRANK). All checked out good, D1_6 goes hot only when fuel pump is priming with key in ON position Link to comment Share on other sites More sharing options...
Ωhm Posted February 19, 2023 Share Posted February 19, 2023 These are START/RUN voltages needed for engine running. I'll keep looking, you keep looking, someone else should chime in. Link to comment Share on other sites More sharing options...
Pete M Posted February 19, 2023 Share Posted February 19, 2023 the maintenance light is literally just on a mechanical timer. it's purely a reminder that the 02 sensor should be replaced every 75k miles (and so it pops on after 75k and then you need to replace the timer itself which is the clear thing with all the gears located under the dash). it has no other function. you're thinking of the OBD1 system that started in 91 with the HO. Link to comment Share on other sites More sharing options...
Pete M Posted February 19, 2023 Share Posted February 19, 2023 does it start then stop immediately as if the key was turned off? or does it chug a bit and die? does it turn off when the key is turned back to run? or does it stay running for a second or 2 longer? Link to comment Share on other sites More sharing options...
Zadouw Posted February 19, 2023 Author Share Posted February 19, 2023 6 minutes ago, Pete M said: does it start then stop immediately as if the key was turned off? or does it chug a bit and die? does it turn off when the key is turned back to run? or does it stay running for a second or 2 longer? Like the key was turned off, if I jold it in the start position it will start and die repeatedly with the starter engaged. Link to comment Share on other sites More sharing options...
87MJTIM Posted February 19, 2023 Share Posted February 19, 2023 If you give it gas, will it run? If it runs when giving it gas, the IAC may need cleaning or replacing. Link to comment Share on other sites More sharing options...
Zadouw Posted February 19, 2023 Author Share Posted February 19, 2023 20 minutes ago, 87MJTIM said: If you give it gas, will it run? If it runs when giving it gas, the IAC may need cleaning or replacing. No change at all with gas pedal to the floor Link to comment Share on other sites More sharing options...
Pete M Posted February 19, 2023 Share Posted February 19, 2023 I've heard of pumps being able to build pressure, but have no flow behind it. might be time to test for flow. did you say you applied 12v to the pump resistor? Link to comment Share on other sites More sharing options...
Zadouw Posted February 19, 2023 Author Share Posted February 19, 2023 1 hour ago, Pete M said: I've heard of pumps being able to build pressure, but have no flow behind it. might be time to test for flow. did you say you applied 12v to the pump resistor? Yeah, I did it 2 ways. I jumped the relay, then I replaced the relay and put power directly to the power wire coming off the relay to the pump its self. Link to comment Share on other sites More sharing options...
Zadouw Posted February 19, 2023 Author Share Posted February 19, 2023 Just now, Zadouw said: Yeah, I did it 2 ways. I jumped the relay, then I replaced the relay and put power directly to the power wire coming off the relay to the pump its self. Also, not exactly scientific, but I used the pump to drain the old gas out. (Put bucket under the fuel line with old fuel filter dangling down and jumped the relay to pump It all out) it seemed to be making good flow. But again, not exactly a scientific process. 😅 Link to comment Share on other sites More sharing options...
Manche757 Posted February 20, 2023 Share Posted February 20, 2023 Don't know where you got the fuel pump resistor but the one offered by Rock made by Standard is a coil resistor and will not work. Just jump the wires together. The cps as a safety feature will only allow enough fuel to fill the injectors. It will shut off in case of a leak or crash. If you replaced it, check to see that it is wired correctly. Correction: the original post stated relay but should be resistor. Link to comment Share on other sites More sharing options...
Armyvet25 Posted February 20, 2023 Share Posted February 20, 2023 A slightly different approach, try and start it with a known good battery, common problem with low voltage, Had a cherokee with same problem till I replaced the battery. Link to comment Share on other sites More sharing options...
Zadouw Posted February 20, 2023 Author Share Posted February 20, 2023 24 minutes ago, Manche757 said: Don't know where you got the fuel pump relay from but the one offered by Rock made by Standard is a coil relay and will not work. Just jump the wires together. The cps as a safety feature will only allow enough fuel to fill the injectors. It will shut off in case of a leak or crash. If you replaced it, check to see that it is wired correctly. Relay is the one that came withe the truck(generic 5 pin relay). But I did jump it from the 30 pin straight to the power pin for the pump and tried to start it with the jumper in place and the pump running full bore, no change. Link to comment Share on other sites More sharing options...
Zadouw Posted February 20, 2023 Author Share Posted February 20, 2023 15 minutes ago, Armyvet25 said: A slightly different approach, try and start it with a known good battery, common problem with low voltage, Had a cherokee with same problem till I replaced the battery. Brand new battery, but I did check that too. Voltage isn't dipping below about 11, maybe 10.5 volts. Never worked on a renix system, but I've never tun into that issue unless it drops below 9 while cranking. But good thought! Link to comment Share on other sites More sharing options...
Pete M Posted February 20, 2023 Share Posted February 20, 2023 not the relay, the pump resistor. did you mess with the resistor at all? Link to comment Share on other sites More sharing options...
gogmorgo Posted February 20, 2023 Share Posted February 20, 2023 I’d definitely be looking at fuel pressure. Being able to push fuel out at the filter doesn’t always translate to adequate pressure at the rail. If you got the truck non-operational or were messing with it at all, it would also be good to double check the ignition switch is aligned correctly. I believe there’s a tip on cruiser54.com for that. Also some other good stuff to check, particularly the ground refreshing. And there’s a tip for an upgraded fuel pump ground as well. If you did get it non-operational, and it wasn’t running when it was parked, it’s very possible someone messing around with stuff left something unplugged or swapped some bad parts in… who knows. Be good to check as many sensors as you can. Crank sensor and it’s wiring for sure would be a good start, followed by the throttle position sensor. It should still start with most of the other sensors faulty. Also I can’t say it applies to Renix, but on a lot of vehicles WOT while cranking is a “clear flood” mode and shuts down injectors. If you’re giving it throttle to start, start at just barely cracking it then working towards 3/4 or so. Link to comment Share on other sites More sharing options...
Zadouw Posted February 20, 2023 Author Share Posted February 20, 2023 34 minutes ago, Pete M said: not the relay, the pump resistor. did you mess with the resistor at all? Yes, the second part of my first response to this was supposed to say 12v directly to the resistor and the wire directly after it to give the pump direct power. I miss typed it, sorry about that. I also have the resistor bypassed with a paperclip at the moment just to make sure. Link to comment Share on other sites More sharing options...
Pete M Posted February 20, 2023 Share Posted February 20, 2023 2 minutes ago, Zadouw said: Yes, the second part of my first response to this was supposed to say 12v directly to the resistor and the wire directly after it to give the pump direct power. I miss typed it, sorry about that. I also have the resistor bypassed with a paperclip at the moment just to make sure. have you tried dumping fuel into the throttle body? Link to comment Share on other sites More sharing options...
Zadouw Posted February 20, 2023 Author Share Posted February 20, 2023 4 minutes ago, Pete M said: have you tried dumping fuel into the throttle body? I have not. Wouldn't that just potentially flood it? Most of my mechanical experience is with HD diesel engines, and some fairly new gas engines (like 2000+ at the earliest) Link to comment Share on other sites More sharing options...
Ωhm Posted February 20, 2023 Share Posted February 20, 2023 1 minute ago, Zadouw said: I have not. Wouldn't that just potentially flood it? No, it would just help prove out that you have a fuel delivery problem if engine tries to stay running. Link to comment Share on other sites More sharing options...
Zadouw Posted February 20, 2023 Author Share Posted February 20, 2023 22 minutes ago, gogmorgo said: I’d definitely be looking at fuel pressure. Being able to push fuel out at the filter doesn’t always translate to adequate pressure at the rail. If you got the truck non-operational or were messing with it at all, it would also be good to double check the ignition switch is aligned correctly. I believe there’s a tip on cruiser54.com for that. Also some other good stuff to check, particularly the ground refreshing. And there’s a tip for an upgraded fuel pump ground as well. If you did get it non-operational, and it wasn’t running when it was parked, it’s very possible someone messing around with stuff left something unplugged or swapped some bad parts in… who knows. Be good to check as many sensors as you can. Crank sensor and it’s wiring for sure would be a good start, followed by the throttle position sensor. It should still start with most of the other sensors faulty. Also I can’t say it applies to Renix, but on a lot of vehicles WOT while cranking is a “clear flood” mode and shuts down injectors. If you’re giving it throttle to start, start at just barely cracking it then working towards 3/4 or so. I put a fuel guage on the schrader valve on the rail and was getting 40psi when cranking and after it died, seemed to be holding the pressure fairly well. The ignition cylinder was drilled out (the lot I got it from got it at auction from I believe a mechanics lean) could that have caused something to be out of wack? I tried holding it in the start position to see if it was a problem with the run circuit to no avail. But I'll didn't see anything about how to check the alignment of it at that link, but I'll do some searching. The ground clean up stuff seems interesting and I will have to give that a go. Would be good to do even if it's not the issue. I've been trying to eagle eye any connections and wiring, especially anything tied to ignition/fuel. But I honestly don't know what all redundancies are built into it that may be causing it to shut its self off. Throttle position sensor may be my next goto though sense 0/10/20/50/100% throttle doesn't seem to make any difference at all with the rpms it fires off at. Link to comment Share on other sites More sharing options...
Zadouw Posted February 20, 2023 Author Share Posted February 20, 2023 13 minutes ago, Ωhm said: No, it would just help prove out that you have a fuel delivery problem if engine tries to stay running. Ok, how much fuel would you say to put in? I can give it a shot. Link to comment Share on other sites More sharing options...
Ωhm Posted February 20, 2023 Share Posted February 20, 2023 3 minutes ago, Zadouw said: Ok, how much fuel would you say to put in? I can give it a shot. Just enough to see if it stays running. Not much. You could even use a spray can of starting fluid. Link to comment Share on other sites More sharing options...
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