Stumble/Misfire on first start of the day

Like the title says, it stumbles/misfires on the first start of the day, usually within 30 seconds of starting and only for about 5-10 seconds. Happens regardless of shift position and engine loading. I'm assuming it has something to do with the fuel system.

It's a 98, stock, 154,000 mi. After it's warm and shut down for a period it doesn't like to start which I believe has something to do with a check valve in the fuel pump which prevents fuel from flowing back into the tank. Could this be the problem? On the first start of the day it cranks for about 3-6 seconds and starts, it then only stumbles after it's been running for a while, not immediately after start.

Any thoughts?

Sounds like a problem that you just have to let get worse to be able to diagnose. Fuel check valve is possible. If you wanted to, you could chase it more with a fuel pressure gage on the fuel rail.

Two separate problems?

I would agree with your idea on the check valve for the long start.

Does your 98 have the IAC? It might be sticking.

Forgive me,

How does a sticky IAC affect this? I'm not quite sure how it works, I understand that it controls the idle (I think anyway) and I know it's never been cleaned. Perhaps I'll start there with some throttle body cleaner...

rockjockphatts said:

Forgive me,

How does a sticky IAC affect this? I'm not quite sure how it works, I understand that it controls the idle (I think anyway) and I know it's never been cleaned. Perhaps I'll start there with some throttle body cleaner...

Click to expand...

Maybe I'm misunderstanding your original problem.

You say when you first start it stumbles/misfires--your IAC controls air mixture. If you have a crappy idle and attempt to give it some throttle, you will get a crappy result. As things warm up, IAC loosens up and starts working better?

I'm sorry I may not have been as clear as I thought...

The stumbling/misfires occur only on the first start of the day and only within 30 seconds (more like 20) of starting. The stumbling will only then occur for no more than 5-10 seconds (closer to 5). Lately my idle has become smoother than in recent years, however that's at operating temperature. Cold idle is still the same (other than the stumble of course). When increased power is applied the RPMs will increase but they don't want to, if power is already being applied the RPMs will drop and you can tell it's stumbling.

The suggestion to clean the TB and IAC is a good one, it needs to be done, I recall while swapping a new exhaust manifold thinking that I needed to clean it...that was two years ago .

The quoted post is in regards to how the actual IAC works. I don't know all that much about it other than it controls the airflow at idle to maintain proper RPM. I just don't know all that much about it...maybe that's all there is to know?!?!

I'll start there and see what happens. Thanks

The IAC controls the idle speed. If it is dirty, you will have idle and/or stalling issues. Clean it and you will notice an improvement.

The starting issue is most likely the check valve or possibly a leaky injector. The check valve failure can also lead to vapor lock in the fuel rail, difficulty starting, and engine stumble for the first 15-30 seconds or running.

Do this: turn the key to ON, wait 5 seconds turn the key to OFF. Turn the key to ON, wait 5 seconds and then attempt to Start. This will prime the fuel system and should give you shorter cranks times and faster starts.

Sounds like i have a similar problem. I too have a 98 XJ that has starting issues. Mine is a little bit different though. My issue is that mine wont start on the first press of the key for 10+ seconds. I usually have to turn off the key and then back on again at it starts right up. Would mine be the check valve then, or IAC related? Would i have to pull the tank? The last owner actually put a new pump in less than 10k miles ago.

Thanks for the help guys.

Sounds like a check valve issue.

The fuel pressure regulator/check valve/fuel filter is a one-piece unit, sits on top of the fuel tank, and you have to drop the tank to get to it.

If you cycle the key ON and OFF a few times and it starts right up that is a pretty good sign that the fuel system is losing pressure.

You can confirm with a fuel pressure gauge. Hook it up, run the engine, shut it off and time how long it takes for the pressure to drop significantly.

Good luck.

Thanks. What would be a good cut off time frame in determining if its good or bad?

You should have 49.2 + - 5 psi engine running. After shut off the pressure shouldn't drop below 30 psi for at least 5 minutes.

This info from the 97 FSM, should be identical to your 98.

You can have a IAC related issue without the IAC being bad. There is a relay that keeps the battery power connected long enough for the computer to adjust the IAC to the correct starting position for starting when you turn off the engine.

From what you are saying, I would bet on a leaky injector flooding one cylinder as it sits for a while. The IAC shouldn't cause rough running once it starts since you are controlling the air with the throttle.

Thanks. I tried playing with the ignition yesterday and i noticed that turning the key to on for 5 sec and then starting it i had zero issues. Once again that leads to check valve right?

yes

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.

Great post Birch! Much appreciated! Will do.

Was there ever a fix to this for the OP?

I am having what seems like the exact same situation. First start of the day, after it cranks and starts to idle with in a few seconds it will stumble and want to stall but never stalls. If I give it a bit of gas it still stumbles and doesn't want to increase RPM. That lasts for only a few seconds then it idles smooth and strong after that initial stumble.

I always assumed my check valve was shot (have all the symptoms for that) but maybe it's an injector flooding a cylinder causing the stumble? Or, is it just 2 separate issues and maybe the IAC is causing the stumble on start up? Rockauto.com has the IAC for pretty cheap if that maybe the problem or not I might just replace it.

iwannadie said:

Was there ever a fix to this for the OP?

I am having what seems like the exact same situation. First start of the day, after it cranks and starts to idle with in a few seconds it will stumble and want to stall but never stalls. If I give it a bit of gas it still stumbles and doesn't want to increase RPM. That lasts for only a few seconds then it idles smooth and strong after that initial stumble.

I always assumed my check valve was shot (have all the symptoms for that) but maybe it's an injector flooding a cylinder causing the stumble? Or, is it just 2 separate issues and maybe the IAC is causing the stumble on start up? Rockauto.com has the IAC for pretty cheap if that maybe the problem or not I might just replace it.

Click to expand...

This is most likely the check valve or a leaky injector. Did you follow the troubleshooting tips I outlined earlier in this thread. If you do, that will help you isolate this! This does not sound like the idle air control.

birchlakeXJ said:

This is most likely the check valve or a leaky injector. Did you follow the troubleshooting tips I outlined earlier in this thread. If you do, that will help you isolate this! This does not sound like the idle air control.

Click to expand...

I've had the check valve symptoms for a few years now. I turn the key to On 2 times before starting and it cranks over instantly. I don't have a pressure gauge though, that will be next.

So it could be the injector leaking and is flooding a cylinder and when I start it's having to push out all that fuel? I'm not sure how the leaking check valve could cause this though, once the fuel is primed back it should be fine.

From my experience, if you have an extended crank time and priming helps it and it starts CLEANLY, the problem is usually the check valve.

If you have an extended crank time and priming helps it and it starts BUT STUMBLES for a while, the problem could be the leaky fuel injector. The stumble/rough running for a little bit after it starts is very possibly the cylinder with the leaky fuel injector running rough as it is flooded with excess fuel...... and takes a bit of time to burn it off.

GET A FUEL PRESSURE GAUGE (they can be rented), FOLLOW THESE TIPS AND FIND OUT FOR SURE!

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.