'88 4.0 - Crank no start

Cranks fine but won't start. In the past year I've put a fuel pump, filter, fp regulator, plugs, wires, cap & rotor, lots of underhood wiring, MAP, IAC, TPS, CPS, injectors and it has been running great for about 8 months since I finished all that stuff.

Parked it a week ago and tried to start it yesterday, it cranks fine but won't start. Tried jumping, it cranked a little faster but no start.

Have done a search but nothing of use turned up. Suspect either a lack of spark or a bad tank of gas - is there a fuel additive that's better than another that I should try (dry gas, etc)? And what's the best way to check for spark?

Thanks for any advice -

CR

The first step would be to check for spark. Pull a spark plug wire off of the spark plug and if you have a spare spark plug, install it into the plug. Find clean spot on the block or head to ground the plug to. Have someone crank the engine over and watch for spark. If you still have no spark, check for spark from the coil. Do this by pulling the coil wire off of the distributor cap and hold the exposed metal part of the wire about 1/4" away from the block and have someone crank. If you have spark, fuel is next. I like to use pull the air intake tube off of the throttle body and spray a small shot of throttle body cleaner (carb\choke cleaner) into the bore and try to start. Starting fluid will work, but it's a bit harsh. If the engine starts, it's a fuel problem. Start by checking fuel pressure. Anywhere in the mid 30's and up should start, although may not be ideal for running properly. If you have good fuel pressure, look at the gas. At my shop I have seen a few cases where customers have filled up and have a lot of water in their gas straight from the pump! If you suspect that this is the case, then get a clear bottle and pump some of the gas into it. Let it sit and see if it separates. The water will be on the bottom. Hope this helps.

Thanks, will give that a shot. We did have some terrible rain come through a week and a half ago, it wouldn't surprise me at all if the tank on the jeep or the tank at the station got some water into it.

Checked for spark yesterday, asked the neighbor lady to crank it while I looked for spark and I'll be damned if it didn't start right up. The only thing I had done was snugged up the CPS connector before I removed the spark plug - that could have been all it was, or it was just being a grumpy old jeep. Or she's got the magic touch - I told her next time it wouldn't start I was coming to find her.

I let it run a half hour and ran down to the gas station to fill it with (hopefully) good gas. So far, so good.

CRJeepin said:

Checked for spark yesterday, asked the neighbor lady to crank it while I looked for spark and I'll be damned if it didn't start right up. The only thing I had done was snugged up the CPS connector before I removed the spark plug - that could have been all it was, or it was just being a grumpy old jeep. Or she's got the magic touch - I told her next time it wouldn't start I was coming to find her.

I let it run a half hour and ran down to the gas station to fill it with (hopefully) good gas. So far, so good.

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the cps wiring harness is a very common problem and is mistaken for a bad cps. make sure you clean the terminals with electric contact cleaner and apply a dab of dialectric grease. at some point though, you might want to think about installing a new cps if its the original. not sure of the year xj, but there is a replacement wiring harness.

I replaced the CPS about 6 months ago, I did clean the terminals and coat with dielectric grease. The terminals were fine but if I recall the stupid external clip on the connector snapped off, which is probably why it loosened up. I'll have to remember to wrap it with some vulcanizing tape, that'll hold it together.

CRJeepin said:

I replaced the CPS about 6 months ago, I did clean the terminals and coat with dielectric grease. The terminals were fine but if I recall the stupid external clip on the connector snapped off, which is probably why it loosened up. I'll have to remember to wrap it with some vulcanizing tape, that'll hold it together.

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same thing happenned to the cps harness on my 89. im using a cable tie to hold it together.