or is it something else...

I can start my Jeep fine and idles perfect. So far the longest distance I've driven it was about 10 miles, near the end of that trip it stalled at a stop light and wouldn't restart. Appeared to have fuel but no spark. Thought I fixed the problem the next day by cleaning up a couple Maxi-fuses under the hood, but then...

Now I can seem to start it and it runs fine. I only feel safe to drive it short distances which it does okay. Its when I try to restart it within the next 30 minutes it will not start. Cranks but no fire, does not even sound like it wants to start. Come back the next day and it starts fine. Last thing I tired yesterday was I started the Jeep and let it idle until it warmed up and the aux fan came on. Shut it off and was able to immediately restart it. Left it sit for about 20 minutes, came back and it wouldn't start on the first try. Second try I cranked it longer than normal and it eventually started and ran okay. But I did not drive it or do anything else.

The problem is almost certainly caused by heat, but I'm not sure if it's a sensor, ignition coil, or a heat soak problem.

Vehicle in question it a '97 4.0L with a '99+ intake manifold, Dodge Neon injectors, and a Banks header.

 

Afternoon bump in case people aren't reading past the first page..cause I don't sometimes.

 

By definition of heat soak - yes.

But not the gum wrapper cure.

That's the typical crankshaft sensor problem. The time it runs will get shorter and shorter, and the time it takes to recover gets longer each time.

Before blindly replacing - have a close look at the connector to it. If there's ANY corrosion in it, try cleaning it and see if it helps.

Probably about 30% of the time it's the connector, the rest of the time it's the CPS itself. (That connector gets wet being right under the cowl's drip line.)

 

I wish it were that simple, but I don't think that's what it is. Reason is the last time I had a no start condition I did a thorough test of the CPS. I had a steady 5.13V supply and a nice square wave while cranking. I followed the video that ScannerDan has on youtube to the letter and everything with the CPS checked out good (during the no start). The one I haven't checked yet is the cam sensor. I have a spare one so the next time I get a chace to test it I may pop that in and see if it starts. My other suspect is the ignition coil. Could it be possible that when my coil gets hot that it might prevent the Jeep from running?

 

The injector heat soak issue would normally only cause a problem during a engine-off heat soak, because with the engine running, fuel is flowing enough that it wouldn't have time to boil (unless temps are WAY hotter than they should be).

So I'm thinking it's possible you might have multiple issues, one of which may just so happen to be the injector heat soak issue... the other sounds like a fuel pump.

Some have experienced bad fuel pumps that fail after a period of running. Had that issue in a friends car - would run fine when cold, but the longer it ran, the WORSE it ran until finally it would stall and not restart (and this was in the fall). Fuel pump was the culprit.

Check your fuel pressure when it won't restart. Having fuel isn't enough - there needs to be enough pressure to escape the injector during that blink of an eye that the injector opens up.

 

Not saying that the fuel pump couldn't be bad, but it is brand new. I have not checked actual pressure at the fuel rail yet though.

 

Revisited:

So today I had a little more time to fool around with this. Here's what I did:
Started the Jeep up and took it for a short drive, probably about 5 minutes. Just long enough to bring it up to operating temp. Shut the Jeep off and then restarted within a few seconds. No problem. With the hood closed and sitting in the sun I left it sit for 5 minutes. Came back, wouldn't start. Waited 15 minutes.... wouldn't start. Waited 30 minutes... wouldn't start. At this point I opened the hood and checked some temps. With my temp checker about 3" from the fuel rail it measured between 160* and 174*. Fuel line under the intake (closer to the exhaust manifold) the meter read 105*. I tried cooling it down with the air compressor, still wouldn't start (temps were around 145* by this time). Then I took the intake hose off the TB and dumped some gas in it. With a long crank of about 5 seconds it started and remained running. I drove it around the driveway and parked it.

So, am I right to assume that this is a fuel heat soak problem? Is it better to wrap the exhaust manifold or the fuel injectors and fuel rail?

Any suggestions are greatly appreciated.

 

heat soak yes, but not the gum wrapper type.

Where is the fuel pressure regulator?
97's had them in one of 2 places - on the fuel rail or on top of the fuel pump in the tank (rare and expensive).

Those temps are not excessive.

Check fuel pressure when hot while it's not starting. KEY ON, ENGINE OFF.
The kind with the regulator on the fuel rail should be about 45 lbs - engine off. Running it should be about 39 psi.

The "in the tank" kind is closer to 50 psi.

 

You may be onto something rrich. When I was building this motor I was piecing together parts from several motors. I had 4 fuel rails to choose from and I wasn't completly sure which one came on the '97... so I narrowed down my choices to the ones with just one fuel line input. Then out of those I chose the one that was in the best condition. I don't think I see a fuel pressure regulator on my fuel rail. Along with that choice I also had to replace the fuel pump... well I didn't have to but the fuel gauge sender was shot and I figured with over 200K miles on the truck it makes sense to replace the whole thing. It was very simular to the orginal, but not identical. So this makes me wonder... am I operating without a fuel pressure regulator? Fuel rails with a regulator on them will always have two fuel lines, right? My Jeep only has one. All the connections at the fuel pump were correct... I'm going to inspect my old fuel pump and the other fuel rails and maybe take some pictures.

 

I'm pretty sure it's the 'intank' regulator that's mounted on the fuel pump. As I mentioned, its an entirely new assembly. How would heat in the engin bay effect this?

This seems like a fuel delivery/heat problem.

 

Heat from the engine bay won't affect anything that's not in the engine bay. Obviously the fuel pump itself should stay nice and cool, especially when you have a full tank, and if the regulator is in the tank also, then it shouldn't be getting hot, either.

Have a look at the crank position sensor. Common problem on these.

 

From post #8 -
"""""Check fuel pressure when hot while it's not starting. KEY ON, ENGINE OFF.
The kind with the regulator on the fuel rail should be about 45 lbs - engine off. Running it should be about 39 psi.

The "in the tank" kind is closer to 50 psi. """""

that's going to tell you what you have and what's happening.

97's used BOTH types of regulators - rail and pump type - and different fuel pumps - depending on the state it was initially sold in.

If there is NONE pressure will be way too high - not your problem.

If it has the in tank one but it's weak it could be your problem.

Cludged together parts are not always compatible.

The newer 4.0's with the 2 small cats and 1 large one HAVE to have the higher pressure - the higher pump pressure and the in-tank regulator. The required pressure is higher to prevent vapor lock.


Of course the in-tank one is not affected by engine heat. But if it's the WRONG PUMP with the lower pressure - you said it was different - or if the right one is failing --.

Checking pressure will tell all!

Parts houses are notorious for giving you the wrong pump.

But as a "put together" dealers may not be very helpful either. But a pressure gauge will be.

 

Okay, here's my data:

Cold engine, installed gauge, turned the key on, no pressure with priming of pump. Cranked the engine, started right up and fuel pressure climbed quickly to 50psi. Shut engine off within two minutes (engine bay still cool). Fuel pressure held at 45psi.

Started engine again and bumped idle up a little to help heat it up quicker. Once the Jeep was up to operating temp I shut it off and left it sit for about 10 minutes. During this time the fuel pressure eventually dropped to 30psi. At this point I tried to re-start it, no start. Fuel pressure came back up to 45psi while cranking.

Next I began the process of letting it cool down, while ever so often I would attempt to restart it. I left the hood open to help the cooling effect.
Interesting part here: While I was letting it cool down I watched the fuel pressure... over about 25 minutes time the pressure dropped to 15psi.

I finally got it to restart after about 45 minutes. Fuel rail was about 130*, t-stat housing was about 145*, exhaust manifold was about the same. It stumbled at first but quickly came to a nice steady idle and ran perfect (quickly as in a couple seconds). Fuel pressure immediatly came back up to 50psi.
Interesting part two: I decided to turn the truck back off after only letting it run for a minute or two. I again watched the fuel pressure. In the mean-time I rotated the tires on my other car and then went in and ate dinner. I returned about an hour later and the fuel pressure was still above 20 psi. So from this I concluded that the fuel pressure dropped more slowly in the cooler engine bay and it dropped more rapidly in the hot engine bay. It should be noted though, in both cases, cranking the engine over would quickly bring the pressure back up to 50psi.

Oh, and with the cooler engine bay, the engine always started right up.

So what does all this mean? Do those readings help?

 

bump

 

Well, the fuel system won't stay under constant pressure when the pump isn't pumping, so it's normal that the pressure would drop off when you shut it down.

As far as the difference in pressure in heat vs cool, you need a larger sample, a difference of 5 psi could be completely normal.

So it seems your fuel pump is completely fine.

It sure as heck sounds to me like you're experienced two problems.

One is the typical heat soak problem in which the underhood temps climb so high after shut down that the fuel in the injectors literally boils into a vapor, and since vapor won't combust correctly, the engine idles poorly until the vapor is fully pushed out of the injectors. Cycling the key to prime the fuel pump has no effect on this as the injectors would still need to open to release that vapor, and the only time it opens is a very quick blink of an eye when the computer commands it to inject a squirt of fuel. So, naturally, it will take a few rotations of the engine to fully expel the vapor.

The OTHER problem, the shutting down while driving and not restarting, that sounds like the Crank Position Sensor, which is ALSO a common problem. Get it checked out.

As far as the heat soak, the much debated "gum wrapper fix" (which is actually using real heat reflective tape/shielding to protect the injectors from heat) has been known to work. Now we KNOW your fuel pump and pressure regulator are functioning properly, so we can safely assume you're experiencing heat soak.