Extended crank / hard start when hot

Hey there, - Long time reader, first time poster.
I have a 1996 Jeep Cherokee Sport 4.0L , 5-Speed.
I am fairly mechanically inclined, and feel I do myself an injustice when I start replacing parts in a guess-and-check fashion. This is my first Jeep, and my Jeep knowledge is limited. So here I am.

About a month ago, the Jeep became hard to start with an extended crank time of about 8 seconds, but only once warmed up.

When attempting to start after a cold soak, no problems at all. Once the vehicle reaches normal operating temperature, it can be restarted with ease for only a few minutes. After that, the extended crank time comes into play. After sitting for roughly 4 or 5 hours, it will again start with no issues. It should be noted - it never fails to start.

OK, where to begin. In my initial research, I began to think I was facing an issue with the injectors. A possible leak down problem with an injector(s) maybe? I decided to test fuel pressure this evening before getting carried away with anything else.

Here are my notes from this afternoon:
-Jeep has sat for days at this point
-Fuel pressure gauge installed, 0 PSI
-Key on, engine off , fuel pressure jumps to 20psi, immediately drops to
~0 PSI when pump stops priming.
-Performing poor man's prime doesn't net anything according to gauge..
the gauge remains at 0 PSI after poor man's prime
-Engine starts easily, no delay at all
-Gauge waivers around 46-50 PSI at all times engine is running (cold and
warmed up)
-As soon as key is turned to off, pressure immediately drops to <5 PSI

It was too cold for me to be outside past this point.

I've read excerpts from the FSM found in other threads addressing this topic - I know that the pressure shouldn't drop in that fashion.
My fuel rail has no regulator, and is return-less. I know that some 1996 models are weird and the regulator is built into the fuel pump module.
A great thread I am referencing can be found here regarding the 1996 set-up that I have: http://www.naxja.org/forum/showthread.php?t=1107991&highlight=1996+fuel

My question/confusion is:
It sounds like the fuel pressure regulator found in my tank is faulty. I don't believe the injectors could leak down like that immediately, and still run/drive fine. So for now, I am not focused on the injectors. What I am baffled by is what makes this an operating temperature related issue. If the regulator found on the fuel deliver module truly is junk, how come the extended crank issue is not apparent when cold soaked?
What am I overlooking / what else can I test ? I want to clamp off the fuel hose to try and isolate the regulator from the bleed down equation, but my fuel line appears to be metal from the filter, all the way to the rail.

Sorry for the long read folks, I hope that you're still with me.

Any help would be much appreciated!

After reading what I just typed, I question if my hard start issue is even related to fueling. I still think something is fishy with my instant pressure drops.

The fuel pressure regulator might be leaking down, but
your primary problem is most likely the fuel pump. When
the pump brushes wear, they act like that; making warm
starts difficult but cold starts OK.

Pressure testing dosen't tell the whole story, because
once the pump revs up the pressure is fine and the engine
runs fine. It's when the (worn) brushes and commutator warm up
that the pump starts up erratically and dosen't provide
pressure. They're easier to diagnose when they fail
completely...

Very interesting. Makes sense, I've never heard of something like that. I'll have to look into that... What I need to do sooner than later is recreate the hard start condition, and test the fuel pressure at that time...

I'm far from a fuel pump expert, never had any issues with mine, in my 96.

If I was having that issue I'd try to find the coil actuator ground wire from the fuel pump relay and instead of having the PDC switch the relay on and off, I'd ground the wire and have the pump run anytime the ignition is on.

And/or install an in line check valve outside the tank. It may be when the pressure drops to zero, fumes fill the fuel rail instead of liquid fuel. And you have to run the fumes through the injectors to purge it.

If your pump is on it's last legs, like Runnin on empty suggests, good luck finding a replacement pump (no such animal for a 96 on this side of the ocean). I'd be tempted to buy an external pump, make an armored case for it and mount it on the frame rail externally, piggybacking the in tank pump.

Just throwing some possibilities out there.

I don't have a schematic for my 96, I use a combination of a 95 and 97 schematic and usually manage to work it out.

I've heard prices of around $350 for a 96 pump (if you can find one) it would likely be double that here (if anybody had one). Not me, I'd be looking at alternatives. The next major malfunction on my 96 and it is going to XJ heaven.

I seem to recall there being issues with "vapor lock" in the fuel rail. I believe the fix was to install heat sheilds on the injectors. I'll have to access my service info Wed. when I go back in to work to confirm.

The fuel pressure drop is definitely an issue that needs to be addressed. It's possible that the vapor lock could be caused by a lack of residual pressure in the rail allowing a hot engine to boil the fuel in the rail.

And there is the possibility that the crank position sensor is starting to get flaky (some one was going to say it:laugh3. Although, my gut is with you that it's fuel. Be it pump spin down or checkvalve, I think it's in the pump and probably time to drop the tank.

I'll just need some time to research unless some one else finds it and posts up.

P.S. while testing fuel pressure during the hard start, I'd check spark. Try to kill two birds w/one stone.

four_shot said:

I seem to recall there being issues with "vapor lock" in the fuel rail. I believe the fix was to install heat sheilds on the injectors. I'll have to access my service info Wed. when I go back in to work to confirm.

The fuel pressure drop is definitely an issue that needs to be addressed. It's possible that the vapor lock could be caused by a lack of residual pressure in the rail allowing a hot engine to boil the fuel in the rail.

Click to expand...

A co-worker suggested the same thing... The same day that he did, I drove the jeep to lunch after it sat for about 5 hours. Started just fine, drove it to eat less than a 1.5 miles away. Ordered my food to-go, returned to the Jeep after being inside for ~10 minutes, BAM! hard start. I don't think it's vapor lock at that point because of how short the drive on this occasion was. It probably barely got to normal operating temperature, if at all..

StoobyMcdooby said:

A co-worker suggested the same thing... The same day that he did, I drove the jeep to lunch after it sat for about 5 hours. Started just fine, drove it to eat less than a 1.5 miles away. Ordered my food to-go, returned to the Jeep after being inside for ~10 minutes, BAM! hard start. I don't think it's vapor lock at that point because of how short the drive on this occasion was. It probably barely got to normal operating temperature, if at all..

Click to expand...

I'm not saying it is vapor lock, but it could be. The heat leeches from the motor to the fuel rail through the contact points. Along with the hot air blowing on it when the motor warms up.

Also if the check valve is defective and the fuel is trying to flow back to the tank it can create a tiny negative pressure in the fuel rail, lower pressure lowers the boiling point of any liquid. The fuel may tend to turn to vapor, with the heat and negative pressure combined. Just speculating.

I was wondering if your pump to tank flange fuel hose is rotted and has a tiny air leak? And maybe the reason you are loosing pressure so fast? If it does air/fuel vapor could migrate to the rail maybe.

I'd be tempted to disconnect the fuel rail fuel line and blow in it and see what happens. Sure not high tech, but it works.

8Mud said:

........good luck finding a replacement pump (no such animal for a 96 on this side of the ocean).........I've heard prices of around $350 for a 96 pump (if you can find one) it would likely be double that here (if anybody had one). Not me, I'd be looking at alternatives. The next major malfunction on my 96 and it is going to XJ heaven.

Click to expand...

8Mud, you have scared the dickens out of me now, and I
have frantically looked for a 96 fuel pump. Amazon had 1
assembly and I ordered it to have on hand. RockAuto seems
to have a good supply of the Bosch replacement pumps.

Why would you put your 96 out of it's misery? Is there
something else about the 96 model we should know about?

I spoke to a few technicians this afternoon at the dealership where I work.
I don't want to end up chasing my tail on this one. My hard start issue only occurs after vehicle has been driven.. I think my fuel pressure test results definitely warrant a look at the fuel pump and in-tank regulator.. there's a chance my problem could be stemming from the two- even if not, the pump still fails testing. I believe I am going to address the pump and regulator this Saturday, using Anak's write up found here : http://www.naxja.org/forum/showthread.php?t=1107991


The only thing that still bothers me, is Anak, and others who decided replacement was the best option, had problems with extended crank/no start at all times, all conditions. Keep in mind that my vehicle only exhibits issues after warmed up. That's why I am skeptical of it curing my problems.. With that being said, I feel that replacement is in order due to the failed tests that I mention in my OP.

Keep the thoughts coming! Much appreciated thus far.

It seems that you could buy the regulator from various jeep dealers like parts.com. Part # is 53030001.

I didn't see the pump though, they don't have it... You may try quadratek or 4wd, they may have it?

I wonder if you can fit a gas tank from a 97+ in that jeep, and go with a "normal" fuel pump. I'm not sure if this works, or if a 97+ pump will work fine with the 96 injection system... So what I just said may be totally useless.

The 97+ pump (which has the regulator in the pump) should output about 45psi +/- 5%, my gauge reads 47 psi on the 99 I have.

When my pump took a plunge it did exactly like you described, quick starts at cold, super hard starts at warm. That was a cheap china knockout that lasted a bit over 20k... Before that was the original pump the jeep came with, lasted almost 100k, but with that pump it was also hard to start when cold. The one I have is a Mopar part, hopefully will last as long as the original.

Oh, even if you know this already, I'll say it for those who don't, best way to lengthen the life of an in tank pump is to go with as much gas in the tank as possible since this is how the pump cools of, with fuel. A pump with few gallons of fuel in the tank will run hotter than with 1/2+ tank.

Prom3theus said:

It seems that you could buy the regulator from various jeep dealers like parts.com. Part # is 53030001.
I wonder if you can fit a gas tank from a 97+ in that jeep, and go with a "normal" fuel pump. I'm not sure if this works, or if a 97+ pump will work fine with the 96 injection system... So what I just said may be totally useless.

When my pump took a plunge it did exactly like you described, quick starts at cold, super hard starts at warm. That was a cheap china knockout that lasted a bit over 20k... Before that was the original pump the jeep came with, lasted almost 100k, but with that pump it was also hard to start when cold. The one I have is a Mopar part, hopefully will last as long as the original.

Oh, even if you know this already, I'll say it for those who don't, best way to lengthen the life of an in tank pump is to go with as much gas in the tank as possible since this is how the pump cools of, with fuel. A pump with few gallons of fuel in the tank will run hotter than with 1/2+ tank.

Click to expand...

Ah-ha! Finally, someone that can confirm this same problem happened to them. I'm even more excited to get this thing swapped out now!

Very good advice to those who do not realize that fuel pumps are cooled by being submerged in fuel.

Excited to get this show on the road this Saturday :greensmok

8Mud said:

.....I was wondering if your pump to tank flange fuel hose is rotted and has a tiny air leak? And maybe the reason you are loosing pressure so fast?......

Click to expand...

Good point; this was observed on my Ranger last winter when
installing a new pump. The hose coming off the regulator
had a tiny split that could hardly be seen. However, it was
big enough for fuel to spray out with the pump running,
and lose pressure with the pump off. This hose would not
normally be changed when installing a new pump.

Stooby, I think your troubles will be over with a new pump. Be sure and replace that top hose too...

Runnin'OnEmpty said:

8Mud, you have scared the dickens out of me now, and I
have frantically looked for a 96 fuel pump. Amazon had 1
assembly and I ordered it to have on hand. RockAuto seems
to have a good supply of the Bosch replacement pumps.

Why would you put your 96 out of it's misery? Is there
something else about the 96 model we should know about?

Click to expand...

Mostly I'm getting tired of crappy parts. I have around a 50% failure rate on my replacement parts. Jeep OEM parts are always best, but Jeep has just about priced me out of the market, they are typically double the price of say Quadratec parts. It took me three tries to get my last radiator, two were damaged in shipping.

I just replaced a three year old water pump, bearings were shot and it was leaking. My new replacement pump lasted three days and started to seep (crap).

I repaired most all of my floor pans a couple of years ago, took me around 60 hours. They rotted worse and way faster than my Renix. My Renix pans are still good. Chrysler was proud of their new process for stamping out floor pans, it was supposed to make them way stronger. Either the coatings they used were inferior or their wonder process has shortened the life span of those floor pans. Take those carpets up every couple of years and stay ahead of the corrosion!

And I have no idea why, but most of my local parts outlets have just up and stopped carrying XJ parts. They don't even list them in the catalogue anymore. It's not an age thing, they still have CJ and YJ parts (even SJ parts).

I'm going to have to order some stuff from Rockauto and see what the import duties are going to cost me.

Back in 87 I had one of the first Renix XJ's in Europe. Parts sometimes took months to get here and half the time they were 86 parts. I had to keep a fairly extensive parts stock on hand, just in case. I'm not going through that again for a 19 year old vehicle.

My Renix is likely to outlast my 96, I have a good stock of parts saved up.

If I can find a nice four banger TJ I'll likely buy that.

8Mud said:

And/or install an in line check valve outside the tank.

Click to expand...

I would advise against this based on what I have read on the web (IOW, do your own research--all I have is secondhand at best). From what I understand a check valve in a fuel system which does not have a return line is a recipe for a fuel leak. Pressures can spike and there is no way to bleed them off except to consume the fuel. Too many of those spikes and a leak will eventually develop. Pressurized fuel leaks have the potential to lead to bad situations.

Do some searching on check valves without return lines before you try this path.

It was an option I seriously considered, but rejected before I did the repair on my '96. I think the '96 pump/sending unit/regulator assembly is plenty serviceable, in spite of some of the information which is out there. If worse comes to worse (no more parts for the '96 unit) I would attempt to install a GenRight tank and a '97+ sending unit/pump assembly. That is on my wish list.

Anak said:

I would advise against this based on what I have read on the web (IOW, do your own research--all I have is secondhand at best). From what I understand a check valve in a fuel system which does not have a return line is a recipe for a fuel leak. Pressures can spike and there is no way to bleed them off except to consume the fuel. Too many of those spikes and a leak will eventually develop. Pressurized fuel leaks have the potential to lead to bad situations.

Do some searching on check valves without return lines before you try this path.

It was an option I seriously considered, but rejected before I did the repair on my '96. I think the '96 pump/sending unit/regulator assembly is plenty serviceable, in spite of some of the information which is out there. If worse comes to worse (no more parts for the '96 unit) I would attempt to install a GenRight tank and a '97+ sending unit/pump assembly. That is on my wish list.

Click to expand...

Thanx for the heads up. I bookmarked your write up, thanx for putting in the effort.

****UPDATE*****

Been a while since I created this thread. I chose to ride this problem out until it got worse. And last week it got way worse. About a month ago CEL came on, only code was P0171 Bank 1 Lean. No driveability issues. About a week ago, the Jeep began to sputter bad under moderate load. Until finally, I didn't think I'd make it to work the following day.

Replaced the fuel pump yesterday- man oh man what a difference .. all driveability issues that I spoke of in the original post are gone- vehicle starts like a modern vehicle, haha. Spins over twice and fires every time, all of the time. Has an extreme increase in power and power delivery. I erased the code last night to see if it returns, although I doubt it will.

If you think your pump is on its way out and you're questioning replacing it- i suggest do it. I used a Bosch pump from Amazon for $61 shipped. Took less than 45 mins to replace.

StoobyMcdooby said:

****UPDATE*****

Been a while since I created this thread. I chose to ride this problem out until it got worse. And last week it got way worse. About a month ago CEL came on, only code was P0171 Bank 1 Lean. No driveability issues. About a week ago, the Jeep began to sputter bad under moderate load. Until finally, I didn't think I'd make it to work the following day.

Replaced the fuel pump yesterday- man oh man what a difference .. all driveability issues that I spoke of in the original post are gone- vehicle starts like a modern vehicle, haha. Spins over twice and fires every time, all of the time. Has an extreme increase in power and power delivery. I erased the code last night to see if it returns, although I doubt it will.

If you think your pump is on its way out and you're questioning replacing it- i suggest do it. I used a Bosch pump from Amazon for $61 shipped. Took less than 45 mins to replace.

Click to expand...

Did you do anything about the regulator? Ive been having the same issues as yourself and did the process as Anak outlined to no avail (although i used an Autozone pump :doh: )

splatvonzipper said:

Did you do anything about the regulator? Ive been having the same issues as yourself and did the process as Anak outlined to no avail (although i used an Autozone pump :doh: )

Click to expand...

Nope. I chose not to after testing fuel pressure with a gauge I bought from a parts store. PSI was very close to spec when I originally tested it. I was half tempted to replace it anyways while I was in there. The good news is that pump removal takes less than 20 mins since I did not have to drop the tank. So if the regulator needs replacing in the future, I'm not going to be too upset.