• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Hard starting on my 98?

ert01

NAXJA Forum User
Some history:
My 98 XJ has 200 000km on it.
It got new plugs and Accel wires in the last 6 months.
It has an older Optima Yellowtop battery.

The problem:
Recently on a short highway trip my Jeep started to stumble. It would run fine for 10min at a time or so, but then it would start to miss for a bit... maybe 10-15 seconds at a time it would just run rough. It got worse and worse during the trip and would stumble and miss for longer periods of time. Then I had my CEL come on... I pulled over and checked it and it was my TPS showing high (or low maybe, I can't remember) voltage. I reset the CEL and cleared the code. I started my Jeep and drove home without any more issues.

When I got home, I swapped my TPS out with my brothers (his was new a week before). After that, my Jeep would take forever to start... it would just turn over and over but if I let go of the key and let the starter wind back down, then tried again, it would fire right up the second try. It did that very consistently for about a week. First try... nothing, second try, fire up fine. I gave my brother his TPS back, thinking it was messed up somehow. Installed another TPS I had in the garage and it has been the same ever since. First try nothing, second try it starts fine.

Help??
I have no idea what's going on... I have tried 3 different TPS's with no luck. I haven't had a CEL come on since that first time on the highway. I would like to get this fixed soon as this is my DD and I'd like to get this fixed before winter hits up here...

Thanks in advance!
Mark
 
How did you check the CEL the 1st time? Did you put a scan tool on it and pull a P(Powertrain) code?

What you're describing in the latter part of your post sounds like a failed check-valve on the fuel pump. You might try the poor man's prime....Key on for 3 seconds, key off, key on, start. If it fires up quickly with that then I'd be supsicious of the check valve and not the TPS. The original problem could have been the TPS which perhaps you fixed. You may have a 2nd problem here if it's just related to starting and not driveability. How long since you replaced the distributor cap and rotor?
 
The check valve is located on top of the gas tank and is part of the fuel pump assembly on 95.5-2001 vintage 4.0 XJs. When the check valve starts to fail, it reduces fuel pressure to a point where an extended crank 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) way to 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 a couple of seconds
3. Turn key to OFF position
4. Repeat above a two more times
5. NOW crank the engine over

If the engine starts quickly and cleanly after performing this procedure, you may have the check valve issue. If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the bleed down and the 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 this symptom. Sounds strange but it definitely does happen. Have battery load tested if you have any questions; your XJ does NOT like low available battery voltage. Be sure battery connections and posts are CLEAN.

Some troubleshooting tips for extended crank times:

Hook up fuel pressure gauge on the schrader valve on the fuel rail

Start engine and bring to normal operating temperature.

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

Shut engine off.

Pressure should not fall below 30 psi for five minutes.

If pressure falls below 30 psi, it must be determined if a fuel injector, the check valve within the
fuel pump module, or a fuel tube/line is leaking. An adaptor tool/hose included with the fuel pressure gauge can help you with this. Consult gauge manual for more information on this 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 - possibly the check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky fuel injector.

You can limp a check valve problem along indefinitely if you wish as it doesn't mean the fuel pump itself is going bad. Normally, the check valve is replaced as an entire assembly as you have to drop the gas tank to access the assembly. Fuel pump assembly consists of fuel pump, regulator, check valve, filter. If you do replace the fuel pump assembly, purchase a high quality OEM style unit. Some cheap aftermarket assemblies don’t hold up and fail prematurely.
 
I pulled the code the first time using a code reader. I had my laptop with me and I referenced the P code with the service manual.

Hmm... thanks for the pointers. At leas now I have a direction to start looking in. I'll give the "poor mans prime" a try tomorrow and post up what I find.

Thanks!
 
Curious on the TPS, usually not a "hard start" issue.

Just for grinz and giggles, push the accelerator pedal to the floor and hold it there before trying to crank the engine over--this is the "clear flood" position--see if it starts up that way.

Second thing I would look at is cleaning the throttle body and the IAC port and IAC pintle.
 
Back
Top