Random Stall - any thoughts?
 

My 99 XJ8 seems to stall randomly. The car has run fine for several years now and last spring I replaced the fuel pump in it.... after the fuel pump was replaced , the car ran great for many months without problems.

Now it seems it will just stall randomly - just idling in the garage it will stall, fully warmed up.

When it does stall, I press down the schrader valve on the fuel rail to make sure there is fuel pressure and there is. The car will start right up after a stall.

Last night, I had it idling the garage and it would stall after a few minutes of running. I suspected the MAF so I took it out and cleaned it with electrical contact cleaner, disconnected the battery and touched the negative cable to the positive cable - as suggested by others. The problem seems to have improved in that is stalls much less frequently.

I have no codes in the computer.

Before I plop down $100+ on a new MAF sensor, just wondering if anyone might have any other troubleshooting suggestions?

Thanks...

I am not a tech but JapPro told me it must be MAF or in worse case throttle body issue.

I also had random stalls, but it may have been at a different time. Mine would stall while driving. Not to the point of dying, but enough to make it buck and jerk. Ended up being the connection to the throttle position sensor that has been mentioned in these forums a bit. A good cleaning, pinching of connections, and reconnecting, and it's all good now.

Again, may not be same stall you are experiencing, but another thing you can check.

Good luck.

I'll take a look at that but I think that if the sensor was doing something weird I would get a code flagged for it. I wish I just had some clue as to why the car was dying. I like to have something to go on before swapping out $100 parts :-).

Guess I'll plop down the cash for a new MAF sensor and see what happens.

That's what I thought too, but it never threw a code. It would buck enough to prevent a safe crossing at an intersection, and never threw a code.

Again, may be different issue, but I was surprised to find the fix that simple, especially considering how badly it was driving.

Throttle body issues won't throw a code. Try searching the archives on throttle body cleaning or throttle body. Also, what SuperSport says is also good advice. There was a TSB on the throttle body electrical connections and TPS connections on the earlier XJ8. I believe they replaced the connectors later with gold plated ones to fix one issue.

Resurrecting this thread as I am again having this problem.

The interesting thing is that I did not have the stalling problem all winter long. Now that it is warm out, it is randomly stalling.

It will stall even while not in motion (park). The engine will be running fine, then decide to just stop/stall...at idle or if I have the throttle pressed down a little (e.g. 2K RPM). There doesn't seem to be any pattern to it (e.g. no time interval).


I have tried cleaning the TB connections (which looked fine, BTW) and the MAF sensor....with no change.


Additionally, I've replaced the fuel pump last spring so plenty of fuel pressure at the rail when it stalls.

Any one have any troubleshooting suggestions? I am kind of spitballing now....thinking of things like water in the gas tank, O2 sensor problems etc....

Question, Ron - now that it's warmer is it also a lot more humid? I found that my TB connector problem always showed up during times of high humidity and especially when raining. Cleaning the Throttle Position Sensor connectors at the TB fixed it.

I wouldn't say its a lot more humid.....

I have cleaned the throttle body connector, at least what I think is the connector. There is a"big" plug on the passenger side of the TB that I've cleaned a few times now. Also, a few years back I had the entire plenum off (heater hose broke that runs under it) and cleaned the TB/plenum good then. Also, did the breather valves....

Do my symptoms describe a TB issue.... e.g. random stall at idle (and at cruise/higher RPM)?

For me, the plug on the driver side clears it up.

Just thought I would "close the loop" on this.... I figured out what was happening and thought I would pass along my findings to help the next poor bloke :icon_eddie:.

I cleaned all the TB connectors and checked for signs of corrosion etc... nothing.... plugged them all back in, still stalling.

So I went ahead and whipped out my odb2 interface for my laptop, hooked it up took a detailed look at what was going on.

I noticed the short term fuel trim would start at about 8% then creep up to about 15% or so then the engine would stall. So I guess shame on me for not doing this in the first place :icon_redface:

I knew that wasn't right so I figured I had an air leak some where. I looked at the snorkel and sure enough it was cracked on the bottom of the "resonator" tube (or whatever it is called).

I sealed that back up, put it back on, fired it up and stall problem went away. The fuel trims slowly returned to normal (<1%) after idling for a few minutes. It started at 8% or so then worked its way down.

So it appears the problem has been solved. Need to do some road testing though.

I am going to guess that winter air is a bit more dense and the PCM had just enough fuel trim to keep the engine running.....

Back to the drawing board.
 

Well took it out for a test drive and didn't make it very far.... stalled out again (and a couple more times before I got home)...:icon_gunhead:

Yesterday, after sitting for a week, I would start it and it would stall in about 1 minute or so... over and over again.... fixed the snorkel, fuel trims came back into line and it can idle all day long. So I thought I finally got it solved.

Went out this morning...starts up fine, idles for 5 minutes or so before I turned it off.


When it stalls going down the road, it takes quite a bit of cranking to get it to fire back up.....but does. Note this is city type driving.

What happens is, you will be going along then all of a sudden you lose all power (engine struggles just below idle)....try to push on the gas a bit more to keep her going but nothing happens... within about 5 seconds or so it finally just stalls out.


Going to hook up the laptop and try to capture what is happening as I am going down the road. After that, I think I will try disconnecting the MAF and get it run in open loop mode to see if it happens in that state.

Right now I am thinking.... MAF is bad or something is going on with the new fuel pump I installed early last year...or maybe fuel pump relay is sticking...


Kind of beating my head against a wall... any advice or suggestions would be greatly appreciated.

I've attached some data collected during a stall event. Though it is not very telling... (note the units are metric). Also, no codes what so ever flagged in the ECU.

This occurred after a brief 5 or so drive that was uneventful. Once I stopped and was idling, it stalled (same as before).

Also note worthy is that is stalled about 5 times on the same return trip....i.e. once it started stalling it would stall alot. Restarting was a bi*ch also... lots of cranking to get it to fire.

Really sounding like a fuel thing to me.... though pump is brand new.

Seems to run fine when everything is cold....either the outdoor climate or when the car is started.

Could this be a vapor lock thing? I know when I replaced the pump, I replaced a piece of the metal fuel line with flexible hose and they do run pretty close to the exhaust. Any way to diagnose vapor in fuel lines definitively?

Hi,

I am sorry I cannot help you now because I have my Jag trying to be fixed about an excess of gas in the engine. I would like to ask you which devices you use to measure the information from your Jag. On the other hand I would like to ask you if a hard reset has worked.

Best luck.

Check the fuel pressure regulator... that's what I'll be doing.... (running out of ideas)

OK... Why is the fuel pump stopping?
 

I think I have FINALLY identified the issue....

I stuck my head in the trunk as the engine was running and heard the high pitched whine of the fuel pump running...

Sure enough I heard the whine stop, then the engine chug and stop.

At that point I trying swapping around fuel pump relays for fun... nothing changed.

Next I pulled the pump fuse out and put my amp meter across the 2 pins.... fired her up and saw it was drawing about 6 amps.... sure enough the amps dropped to zero and the pump stopped...car stalled.


Is there some reason that the ECU would stop the fuel pump running while the engine is running?

Does the pump have a high pressure limiter or something that would stop itself?


The pump is a brand new Airtex I put in early last year...


(please tell me it could be something other than a bad pump!)

I hope everyone else has resolved their stalling issues.
I'm dealing with a 2003 XJ8. I bought it as a project car and while sorting out all of the other issues I had to have the alternator replaced because the original failed on me without surprise because it was whining very loudly for a few weeks prior.
After having it replaced the car now randomly stalls on occasion when coming to a stop at a light or a stop sign. It has never stalled while just driving down the road at normal speeds, only when coming to a stop does it stumble and die. The only code it has thrown in the past year is P0433.
It never did this before and I'm wondering if the alternator I ordered was not the correct amperage for these cars. I know if the voltage drops too low the fuel pump stops at least that's what I've heard and seems to be indicated.
I should have bought an oem alternator instead of trying to save money.

Sorry to hear your stalling problems. My engine is the 4.0 V8 Supercharged.
I had exactly the same problem, no codes and very random.
Turns out it was the throttle body - as a bonus this also fixed my gearbox issues.
A nice second hand one for £150 sorted it.

Good luck.

Check your knock sensors!