Need some real help here with engine not starting

I've been reading for the past two days all the no start threads on this site and several others. I can't come up with what's going on with my issue. I bought a running '91 4.0 heard it run and actually started it myself many times before I pulled it out. I tore it down and had the head rebuilt. Put all new gaskets on it and put it back together. Put it in my '91 Cherokee. It cranks, has spark, has fuel to the rail. I've replaced the CPS, Coil, plugs, wires, cap and rotor. I get a good spark and I get fuel gushing at the bleed off valve(whatever it's called) and good stream from at the lines when cranking.

I'm at a loss. Someone please tell me it's something little I'm overlooking.

I also replaced the throttle body with the censors from another intake just to see. I've put a new interstate battery on it.

It will try to start when I hold the gas all the way to the floor. It's as if it's not timed right but I never moved or took the distributor out when doing the work to it.

Any help would be great.

I've also checked the relays and switched them around. Checked all fuses.

seems as if you have done everything possible,recheck your wires for firing order maybe you got a couple of them in the wrong firing order,.also i have heard of faulty cps units that are bought at auto parts stores,the dealers are a little higher but worth it.if you go to JeepCherokeeForum site,there is a thread that tells you how to bypass your cps to see if its functioning right,also check to see if your reverse lights come on,your neutral switch may need cleaning,hope this helps.

First off, pull all the plugs and clean them, then ideally bake them in your oven at 350 for an hour or two to dry them out. Wet fouled plugs are the kiss of death for getting a 4.0L started.

Try a short crank to see if it starts. If not, have a buddy spray some starting fluid or carb cleaner down the intake. If it fires, you are not getting fuel (injectors not working or no fuel pressure)


Most likely if you pulled the distributor, you have it indexed incorrectly. I would also verify the firing order. First crank the engne over by hand to roughly 14 degrees BTDC and pull the distributor cap. The rotor should point at cylinder #1"s plug wire or 180 degrees away. If that doesn't show any problems, pull the #1 plug and have a buddy turn the engine by hand until it comes up on 14 BTDC and with your finger in the spark plug hole, you can feel the pressure escaping due to being on the compression stroke. This time the rotor should definately be pointing directly at the #1 plug.

While you have the cap off, look inside and make sure the carbon button in the top is still there. I have seen more than one engine where the little button fell out without anybody seeing it and presto, no start.

I did check the reverse lights and they come on when in reverse. I DID NOT remove the distributor from the running motor. It ran fine before I made the swap. I've pulled the plugs and they're black but not wet.

x2 what OLD MAN says, maybe the dist. was indexed wrong by previous owner and #1 plug wire no longer matches the #1 on dist. cap.

When you replaced the plug wires did you do it one by one?

Anyway, if you have spark and fuel it should flash up.

I would put #1 cylinder at TDC and look at rotor cap to see where it's pointing.

Good luck, post back with progress.

ScoobyDooJeep said:

I did check the reverse lights and they come on when in reverse. I DID NOT remove the distributor from the running motor. It ran fine before I made the swap. I've pulled the plugs and they're black but not wet.

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Put a cheap set of Champions in it and try again. They should not be black.

Ok, I changed plugs and checked the timing. Timing is right. It did start after I pushed the pedal all the way to the floor. It ran for about 30 seconds but I had to keep pushing on the pedal then it just died. Wouldn't restart. I'm beginning to think it's fuel related even though I get a good flow to the injector rail. How can I tell if the injectors are firing?

Possibly the TPS if pushing throttle down made a difference. Pull connector off and clean it.

ScoobyDooJeep said:

Ok, I changed plugs and checked the timing. Timing is right. It did start after I pushed the pedal all the way to the floor. It ran for about 30 seconds but I had to keep pushing on the pedal then it just died. Wouldn't restart. I'm beginning to think it's fuel related even though I get a good flow to the injector rail. How can I tell if the injectors are firing?

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There is something called a NOD light. You plug it between the injector and the cable and you can watch it light up as power is fed to the injector. HF has a cheap set.

What you said about holding the pedal all the way down sounds suspicious. If you do that before you start cranking and hold it down, it tells the ECU to shut off the injectors to help clear a flooded situation. Black plugs say you are running way too rich.

My next thing to check would be for a plugged CAT. You can do that with a vacuum gauge (one of the primary troubleshooting tools of old shade tree mechanics). Another quick way is to pull the O2 sensor and see if it starts. If the CAT is plugged, it gives an alternate path for the exhaust.

Thanks for the replies. I'll try them sometime this week. This is going to be a busy week for me at work. I'll post more as I know it.

Thanks again....

old_man said:

There is something called a NOD light. You plug it between the injector and the cable and you can watch it light up as power is fed to the injector. HF has a cheap set.

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NOID light. It goes in place of the injector on the harness, not between.

Talyn said:

NOID light. It goes in place of the injector on the harness, not between.

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Not necessarily. The set I had for Ford actually went between and there was one for each cylinder so you could start it up and run it through its paces.

Thats neat. Never saw those. Are they a Ford tool?

It's been 20 years. Can't even remember where I got them. If I had the connectors, I would make a new set. Actually I was thinking of making a set with the lights in a row on a little bar that you could tuck under the wiper so you could test drive it and see it while you drove.

Well, unhooked the exhaust and tried to start it. That didn't make any difference. I'm smelling fuel now and the new champion plugs are somewhat wet. I'm thinking it's getting way to much fuel or it's not getting enough spark. New everything in the spark department so I'm not sure that's it. Maybe to much fuel?

Just a thought on my part....but
Could the fuel pressure regulator have a part in the mix of things?
That is, if the injuectors are working properly.....................

B.RAIDER said:

Just a thought on my part....but
Could the fuel pressure regulator have a part in the mix of things?
That is, if the injuectors are working properly.....................

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I'm sure it could and I've thought of that but I'm trying to weed out anything else before I look there. Shame I don't have someone close that I could borrow a good one from before I spend $60 on it.

ScoobyDooJeep said:

I'm sure it could and I've thought of that but I'm trying to weed out anything else before I look there. Shame I don't have someone close that I could borrow a good one from before I spend $60 on it.

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You can get a el-cheapo fuel pressure gage to check that.

That's how we found my sons fuel pump was out.

I'm sure it would tell you whether the regulator is out of wack as well. You can check it with the vacuum and without to see if it is within specs.

I just recently installed a new fuel pump due to a lack of starting. FYI, do NOT buy an Airtex.

Here's a way you can tell if you're lacking in fuel pressure. Cycle the ignition from the Off position to the Run position about 4 times. You'll hear the fuel pump prime for about a second. So when you cycle to run let it sit for about 2 seconds, then do it again 3 more times.

If it starts up after that then you're bleeding fuel pressure back through the pump. There's a valve on it (I forget the terminology) that keeps the fuel from bleeding back through the lines.

Also, if you've just had headwork done then it's probably been sitting a while and has leaked all the pressure out regardless of whether or not that valve is worn or not. When I rebuilt mine I had to cycle to the run position a few times to pressurize the fuel system and my pump worked just fine then.

And even when I recently replaced my fuel pump I still had a decent amount of fuel-spray at the fuel rail when I was relieving the pressure so I didn't get a surging shower from the lines at the tank while I was down there. So don't let the term "gushing" fool you. I had what you consider as "gushing" at the fuel rail, but I still leaked a decent amount of pressure. Enough that I would turn the key for 10-15 seconds about 3 to 4 times before I could finally get it to crank.

Once I found out the easy way to test the fuel pressure via the cycle method though I just used the poor man method until I got the pump.