heatsoak? fuel pump? Please help!

Hey guys, please take a minute to read, I just got my new XJ and am not very mechanically inclined. I also have read thread upon thread, upon thread on here and Cherokeeforum. Nothing seems "just like" my problem.
Here we go!
I just bought my 2000 Cherokee Sport 3 weeks ago. Drove it home from Philly to Minneapolis MN. Ran GREAT the whole time. The only problem was it seemed to take a few cranks too many to start. A few days later, I got a CEL, so my buddy checked the codes and it was saying Misfire on cyl 5. So I started with replacing the plugs and coil rail (The plugs were terrible, so I'm glad I got that done). After replacing that stuff, I still got the delayed starting, and it has gotten worse. However I'm not sure if it's like the heatsoak (even though after much reading, I'm still kind of confused on exactly what that is). After far too many cranks it finally starts, but runs a bit rough. A few kicks of the gas pedal smooths me out nicely and I'm good to go. Never any hesitation going down the road or anything. I also have tried "the poor mans prime" or w/e its called. Turn the key to the on position and letting it sit for a few seconds before starting. Hell I've even turned it to on, then off again, to on, repeat up to 4 times and then tried starting. Doesn't start right up like it should. I'm extremely frustrated but don't have the money to just start replacing stuff without a reason. Friends, and family (whom are kind of mechanically inclined) have mention fuel filter and pump. I'm more inclined to injectors, just based off what I have read. Please help me out. I'm a student, and while I'm trying to do hw, I find myself drifting to this forum and others to try and narrow it down some more. Thanks so much in advance. And if anything needs more explanation, I'll gladly add more.

it's most likely the check valve in the pump assembly, a very common problem in the late models. The crappy part is the only way to fix it is to replace the whole assembly.

Since you mentioned you're not very mechanical i'll explain it best as i can. a check valve is sort of a one way valve, this one happens to be part of the fuel vapor evap system (emissions crap) when it fails, as the jeep sits the fuel system loses pressure and allows the fuel to drain back all the way from up by the engine where the injector rail is, back into the tank. the reason it takes longer to start is the pump has to refill and re-pressurize the entire fuel system before it can start firing the injectors.

as I said this valve is part of the fuel pump assembly and in order to fix it you need to replace the entire thing. this involves dropping the gas tank and pulling the old one out, dropping the new one in, and you're done.


I can't tell you 100% that this is your problem but the long crank before starting on a late model XJ is 99% of the time the fuel system check valve failing. If you do replace the pump make sure you get the entire assembly, and STAY AWAY FROM THE AIRTEX BRAND. they're crap, the longest i've seen one last is 8 months. Rockauto.com has about the best price around on a good brand carter pump, bosch is also good but more expensive.


good luck.


PS: heat soak is the fuel overheating in the fuel rail and causing air bubbles to form, it only happens when you drive around, get it good and hot, then park it and try to start it again before it cools down. it makes it run like crap for a few minutes, thats all.

See, I read that somewhere, but the "poor mans prime" was supposed to help with that, I thought. I've seen all over that the check valves go bad quite often. But wasn't sure if this was my problem. Thanks for your reply. I will probably go ahead and get a new pump assembly ordered. I appreciate your help on Brands as well, Airtex was the only thing I've really seen, but will check RockAuto.

I'm not 100%, but I've heard that the fuel pumps are "all in one" units...is this the correct part for my 4.0?
http://www.rockauto.com/catalog/moreinfo.php?pk=452971&cc=1363384

yes, the entire assembly is what you want. some places sell the pump alone but your problem is most likely not the pump itself. it's really a poor design but this is what we've got so you're kind of stuck replacing the whole thing.

the only good part about it is the fuel level sensor contacts are pretty famous for going bad as well, so you're killing two birds with one stone here essentially.

Alright cool, thanks for your quick replies. I will hopefully get this done, this week and will update on how it went.

How do you know it's not a leaky fuel injector(s) bleeding off the fuel pressure?

Misfire and it runs rough at start-up.

Through my reading, I actually kind of suspected fuel injector issues...although I haven't had a code recently for misfires. I'm not rich, but I do have the money to get a new pump. It won't hurt anything I suppose. And if the problem persists, I will check more into the fuel rail area.

The check valves (there are two of them; one on the fuel pressure regulator and another on the fuel pump) are part of the fuel pump assembly on 95.5-2001 vintage 4.0 XJs. When a check valve starts to fail, it can reduce fuel pressure to a point where an extended cranking time is needed to start the engine. It is a very common failure. I experienced it on my 99 at around 75K.

A good (and simple) first step in helping you troubleshoot this problem is called “the poor mans prime”

1. Turn key to ON position (do not crank the engine!)
2. The fuel pump will energize and run for about 2 seconds. Be sure to wait until it stops running.
3. Turn key to OFF position
4. Repeat above steps 1-3 two more times
5. NOW crank the engine over

If the engine starts quickly and cleanly after performing this procedure, you may have a check valve issue. If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the fuel pressure leaking down and the subsequent stumble upon startup is the engine clearing the excess fuel that has leaked into the cylinder because of the faulty injector.

Also be aware that a bad battery can give you starting symptoms as well. Have your battery load tested (any parts store will do this for free) if you have any doubt; your XJ does NOT like low available battery voltage. Be sure battery connections and posts are CLEAN.

Some troubleshooting tips for extended crank times. You will need a fuel pressure gauge. Many parts stores will rent you this tool inexpensively.

*Hook up fuel pressure gauge on the schrader valve on the fuel rail under the hood

*Start engine and bring to normal operating temperature.

*Observe fuel pressure gauge. Normal operating pressure should be 49.2 psi (plus or minus 5 psi)

*Shut engine off.

*Observe pressure on gauge. Pressure should not fall below 30 psi for five minutes.

If pressure falls below 30 psi, it must be determined if a fuel injector, a check valve within the
fuel pump assembly, or a fuel tube/line is leaking. An adaptor tool/hose included with the fuel pressure gauge can help you with this. Consult the manual that comes with the fuel pressure gauge and the Factory Service Manual for your year XJ for more information on this exact procedure, but here is basically how it works:

*Turn the engine off and immediately clamp the fuel line at the adaptor hose. Watch the pressure gauge and see how long it takes to lose pressure.

*If the pressure remains at 49 psi for an extended period of time then the problem is in the tank – most likely a check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky fuel injector.

**Note. Where check valve is suspect, a quick loss of fuel pressure is often the fuel pressure regulator check valve and a slow loss of pressure is often the fuel pump check valve. But keep in mind that either or both check valves can be to blame.

You can limp a check valve problem along indefinitely if you like, as it doesn't mean the fuel pump itself is going to fail. Perform the “poor mans prime” before cranking to speed up your starts. However, if you have a check valve issue and want to resolve it, it is recommended that you replace the entire fuel pump assembly for two reasons. First, you have to drop the gas tank to access the assembly. Secondly, with two check valves, replacing just the fuel pressure regulator where one of the check valve resides may or may not resolve your problem; remember there are two check valves; the other one is on the fuel pump.

The fuel pump assembly consists of fuel pump, fuel pressure regulator, fuel gauge sending unit, fuel gauge float, pickup filter and pigtail wiring harness. If you do replace the fuel pump assembly, purchase a high quality unit; you do get what you pay for here. Some cheap aftermarket assemblies have been known to fail prematurely. I personally prefer Bosch fuel pumps as they manufacture the best fuel pump assemblies for the XJ. Carter is my second choice. Airtex is my least favorite choice and I will not recommend or install them.

a leaky injector is also a good place to look. after it's been sitting for awhile pull the plugs one by one and smell for a very strong gas odor. if one cylinder's plug smells much stronger than any of the others this will tell you if an injector is bleeding off into the cylinder.

GrimmJeeper said:

a leaky injector is also a good place to look. after it's been sitting for awhile pull the plugs one by one and smell for a very strong gas odor. if one cylinder's plug smells much stronger than any of the others this will tell you if an injector is bleeding off into the cylinder.

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This. Especially if the priming of the fuel pump doesn't work.

Hey guys, yea I was thinking that too. Probably gonna replace the fuel pump, and the injector(s) on the cylinder(s) that are misfiring. Already bought the pump. Are injectors from Auto Zone, or Advanced Auto any good? Any brand preference from anyone?

you could get parts store injectors and they seem to work out just fine. if you do some reading up on injectors you can find a set of the 4 hole bosch style injectors and get a better spray pattern and possibly a little bump in power and fuel economy - and it's about the same price as buying new ones from the parts store.

I'd pick up a full set of new/matched injectors from eBay. Maybe $120-130 for the full set w/ o-rings. Not bad.

Also, I had this problem w/ my '99 over the past few months. I installed a new OEM (Bosch) fuel pump - fixed it right up. I have 119k on my '99. There is a seller on eBay w/ these pumps for a low price - like $120/shipped. If you need a link to his auctions, let me know. (not me!)

DO NOT get some junk (airtex) pump, you'll be pulling the tank again shortly.

JumbaXJ said:

Hey guys, yea I was thinking that too. Probably gonna replace the fuel pump, and the injector(s) on the cylinder(s) that are misfiring. Already bought the pump. Are injectors from Auto Zone, or Advanced Auto any good? Any brand preference from anyone?

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I'd just pull the rail, with the injectors still attached.

Prime the pump a few times but don't start it, and then replace any ones that you see leaking or seeping.

Who knows the misfire may be unrelated.

Before getting into the guts of the mechanicals, I would run a can of BG44K through the gas. I run a can every 10k miles in every vehicle I have. It cleans up the injectors and gets rid of built up carbon. It will normally help mileage as well by cleaning the injectors. If you have a sticking injector, it will most likely clean it up.

If it fixes the problem, great, but if not, it never hurts to clean up the system.

I hate to be the guy with the bad news....but dollars to donuts you need a new head. Sorry. I chased this problem for nearly a year. First a misfire on 5...then later on 3 and 5. The sometimes 2, 3, and 5. And other times P03000: random misfire.

I chased the IAC, cleaned the throttle body, swapped the coil pack, swapped the IAC, TPS and MAP with salvage parts, put on a new Crank Pos. Sensor (need that anyway). Re-keyed the cam-position sensor.

It was head all along. Go and pay a mechanic for a compression test right now. Stop running in circles. For $60-100 you can get a compression test on each cylinder and a scope stuck into each cylinder to check for scoring, etc.

You probably have low compression in one or more cylinders. I had it on three. The 99's, 00's; 01's seem to have chronic head problems. My 0331 head was NOT cracked. In fact.... I have it sitting in my carport and will sell it for $150. YOU pay shipping or pick up. It needs a rebuild.

IF you need a head, here is what I did: Ordered a salvaged 2005 Wrangler head. $220. Paid to have it rebuilt. $240. $460 for a factory, upgraded, tupy head. NOT a recast. No slag. No crap. No worries. And not a bad price, considering.

I am not a mechanic. Individual results may vary. But your problem sounds exactly like mine and all the suggestions here are the ones that everyone suggests......and they are all very good suggestions IF your head is not worn. You probably have worn valves. A jeep with this issue will run perfectly fine at speed. It will idle fine most of the time. But it will idle very rough sometimes and throw a CEL. A couple of restarts, or the next day it will drive fine again. But ALWAYS runs fine at speed on the Interstate (as long as you get there before you get it real hot).

It is not fuel pressure, coils, plugs, sensors, TB, or otherwise. It is the head. Or at least it was for me. Go have it tested.

Sorry if I am completely wrong. But I wish someone had been this firm and direct with me 10 months ago. Would have saved me a lot of trouble. Get a compression test. And that is an order!

JG

BTW---YES....the later model Wrangler tupy heads (at least up to 2005) are a DIRECT swap into the 99-01 xj. Every bolt, hole, etc are the EXACT same. Nothing to worry about. Period. It IS the same head. i promise. It is a direct swap.

BTW---I had the "heatsoak" problem also....but it cleared up with the new head. And I put the Jeep Neon/Bosch 4-hole injectors in from eBay. No change. It was my head.

I did not have the long start....but I did have the rough start until I goosed it a couple of times. It seems I remember reading somewhere that the "poor man's prime" does not work on the 99-01 models....but I could be VERY wrong about that. But I know this: despite the several hundred people online who have posted fuel pressure/pump/check valve issues.....it is actually not that common of a failure when looking at the number of XJ's from those years vs. the number of failures.

But the heads....THAT is a different story. EVERY, SINGLE head from the 2000 XJ is going to fail. It is only a question of when. It could be why yours was for sale in the first place. But if it DOES turn out to be the head....don't let it spook you. The XJ is nearly bullet-proof. As long as you have good oil pressure.....do the head work. It will be worth it. The damn things run forever. AND.....you really could replace the head yourself. Or pay a mechanic about $350 to do it for you. You will also have to purchase gaskets and bolts. To pay for parts and labor for someone else to replace your head....including the cost of the head....the price is about $1000 to $1200. It is what it is. Do it your self for $600-700.

Again...sorry if I am wrong. It may not be the head. But it probably is.

How about some actual diagnosis instead of regurgitating everything you've ever read on naxja.

I don't know how you got from long crank to zomg must have a cracked head that fast.