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88 Renix MJ not starting.

2

256Chilipepper

NAXJA Forum User
Location
Huntsville, Alabama
Hello, I bought an 88 MJ 4.0L auto, 4x4 couple weeks ago. Body is straight as can be with NO RUST! :wave:
The previous owner blew the rings in the stock engine with 285k miles. He swapped in a 94 block and head, kept the old intake and exhaust and the entire renix system. But he never got it running again. He did put in a new cap, rotor, wires, and thermostat.
After I put in a new battery, fuel pump, radiator, starter relay, thermostat, and plugs, distributor, and topped off all the fluids, it still won't start. Its getting spark, and the fuel injectors are firing. It is getting fuel to the fuel rail also. There is fuel pooling up in the intake manifold, but it won't start. Cranks and cranks, tries to sputter to start, but it never will.

I went out tonight and tested the crank sensor, the coolant temp sensor, and intake air temp sensor. They all check out fine. Ive also checked the grounds, but maybe i missed one.

Any ideas to why it won't start? Im baffled.
 
does it have the HO head or the renix head?

Have you double checked the timing, if the head was off there's a chance it was not timed properly.
 
87manche said:
does it have the HO head or the renix head?

Have you double checked the timing, if the head was off there's a chance it was not timed properly.
Click to expand...

94 block and head. Head casting number is 7120. Those are the only things he changed. Said he swapped them in as a complete unit. I put the new distributor in, and got it timed in right. Timing is set at 10 degrees.

It fires only 1 cylinder each time it spins around. It really wants to run, but won't. Battery is down a good bit now, so its going on the charger until I can get back to it tomorrow afternoon.
 
he didn't , by chance, leave the HO flexplate on the engine while keeping the renix system, did he?
it'll never run that way. for some reason, I've seen that several times now...
 
Ill have to call and ask him unless there is a way to tell without pulling the motor. The inspection covers between the bell housing and motor are off by the way. Previous owner was pretty lazy and incompetent with this truck, so i wouldn't be surprised if its the HO flex plate.
 
Just talked to the previous owner, he said that he used the original renix flexplate. Any other ideas?

Out of curiosity there is a green wire coming off the post on the starter relay, that splits into 4 red wires. What does that go to? I can't find it in any wiring diagram.
 
Just talked to the previous owner, he said that he used the original renix flexplate. Any other ideas?

Out of curiosity there is a green wire coming off the post on the starter relay, that splits into 4 red wires. What does that go to? I can't find it in any wiring diagram.
 
make sure the ballast resistor is hooked up on the fender well up by the left fender. If its getting fuel and spark it should start but make sure the fuel pump regulator is working you shouldn't have fuel pooling in your intake manifold
 
hmmmm.....that's a good one. all you need is fuel, air, and spark(at the right times) to run. it sounds like you have all three ingredients...
maybe the coil spark isn't strong enough? make sure it's a good, bright spark...or try another known good coil.
your statement about timing seems odd, as it's not adjustable in any way, unless the the locating tabs were cut off the distributor.
it should be installed so that when you're at tdc, the edge of the rotor blade should be *just past* the #1 cap terminal(search "cruisers renix distributor indexing"). it really sounds like an ignition issue to me.
 
No ballast resistor at all on this MJ. Guess they bypassed it. I figured out there is an issue with getting power to the 30 pin on the fuel pump relay. So Ive just been hot wiring the 87 pin to the positive post on the battery to get the fuel pump to run.

Double checked timing today. Dead accurate.

Found out if I let the fuel pump run for 30 seconds, then un hook it, hold the starter (using an old starter button so i can stay under the hood) it will start and run for about 5 seconds, then cuts off. But if I do this, and as soon as it starts to run, re connect the fuel pump it will run for about 20 seconds then cut off. So I figure this is a fuel pressure regulator being stuck wide open and not letting it build pressure. Swapped in one my brother-in-law gave me and the seals on the return line started to leak. Replaced those, and it ran for about 20 seconds. Then it cut off and the seal from the regulator to the fuel rail started to leak. Parts stores are closed, so Ill get to take care of that in the morning.
 
cruiser54 said:
How did you check the timing?
Click to expand...

I pulled the #1 plug out and put my finger over the hole and turned the motor over by hand until I felt compression. Put the dip stick in the cylinder and kept turning until it wasn't coming out any more. Once it was at TDC, pulled the cap and the rotor was pointed just past the #1 node on the cap. Put it all back together, and while turing it over put the timing light on it and watched the timing mark on the balancer and it shows right at 10 degrees while cranking.
 
Dude, I lurk on almost every forum for off-roading, and now autocross. Ill be a more frequent visitor here because of my Comanche.

When I turn the key to start it, it runs for about 3 second, then runs out of fuel. This is usually the fuel pump ballast, but my truck doesn't have one at all. Now I still cant get power from the 30 pin on the fuel pump relay to the 87 pin (fuel pump) with the key in the on position. I get a 14v reading from the 30 pin to the positive post on the battery, but nothing to the negative post. If i jumper the 30 to the 87, the fuel pump doesn't do anything. But if i hook the 87 pin to the positive on the battery post, the pump runs fine. Thats the only way I can make it run.

Anyone have a wiring diagram? I have one from a renix guide, but according to it, my truck should be able to run without jumping the fuel pump.
 
Can you see if the ballast resistor is actually bypassed? And if there is 12v to it or where it should be?
 
mtbxj87 said:
Can you see if the ballast resistor is actually bypassed? And if there is 12v to it or where it should be?
Click to expand...

Don't even see a wire splice or anything. Everything looks factory, and antiquated. A friend of mine has a 90 XJ, and he didn't have one either. Its like it was an option on them, or they were removed a very long time ago.
 
87 was the only year that didn't have them. And even some of those were retrofitted with them by the dealer based on customer complaints of fuel pump noise. You guys know where to look and what they look like? I have a 1987 wiring manual.
 
cruiser54 said:
87 was the only year that didn't have them. And even some of those were retrofitted with them by the dealer based on customer complaints of fuel pump noise. You guys know where to look and what they look like? I have a 1987 wiring manual.
Click to expand...

Should be on the passenger side fender? I've seen a few pictures were its on the drivers side by the air box. There are 2 orange and red wires with he factor spade connectors on them just sticking out of the wire loom over on the drivers side. and a red one with about 3 feet of wire on it over on the passenger side.

What color wires should I be looking for? Im going to try and print the wiring diagrams I can get through work (O'reillys) tomorrow.
 
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