Birty Dastards Jeep Club

Tech Forum => Workshop => Topic started by: PtP on September 17, 2008, 01:45:34 PM

Title: Occasional misfire!
Post by: PtP on September 17, 2008, 01:45:34 PM
I’ve noticed over the last couple of months a random occasional misfire on my 4.0 TJ. I can be driving along at a steady speed with virtually no obvious movement in of the accelerator and out of nowhere the engine will give a split second misfire and then carry on. Sometimes the misfire will then repeat after a couple of seconds or it might not do it again!

I fitted new plugs around 10,000 miles ago and that’s about it on the electrical side of things.

I nearly always give the engine a good jet-wash after it’s been in mud and I’m wondering if I’ve got water in the TPS.

The inside of the distributor is dry and has been sprayed with WD40 as have the plug leads etc.

Anyone had a similar problem or where should I start?
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Post by: eastryjeep on September 17, 2008, 02:16:05 PM
If youve got a crank position sensor on the bellhousing that would be my first guess!
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Post by: JohnFuk on September 17, 2008, 02:26:54 PM
Just had the same thing on a mates VW. It ended up with it being the HT leads.
They were breaking down with the vibration.
Title: backfire
Post by: wildwood on September 18, 2008, 05:49:16 PM
Throttle position sensor (TPS) on the throttle body.
Had this same symptom last year, just as you described.
Swapped out the TPS and no probs again.
They don't like extreme saturation, mine got a dunking at Tong was OK up to then.
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Post by: Dave69 on September 18, 2008, 07:21:57 PM
what you could also do is whip the plugs out and give them a good clean, 10k miles without them being cleaned is alot of miles as i see it
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Post by: PtP on September 18, 2008, 09:36:07 PM
I've done about 20 miles today and it ran without missing a beat. :-)
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Post by: Bubba on September 18, 2008, 09:41:27 PM
start it up in the dark wiggle the leads and look closly at dizzy cap see if you can see any small sparks from the ht system.......wear  a rubber glove if feelin wimpy
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Post by: PtP on September 18, 2008, 09:44:57 PM
Quote from: "V8 Bubba"
.......wear  a rubber glove if feelin wimpy

I'll wet my hands and I should find it a bit quicker! :lol:
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Post by: Bubba on September 18, 2008, 10:01:18 PM
if you are feelin tough use ya tongue
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Post by: PtP on September 18, 2008, 10:11:29 PM
Quote from: "V8 Bubba"
if you are feelin tough use ya tongue

I've got to keep it clean for later! :lol:
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Post by: Dave69 on September 19, 2008, 07:59:03 PM
Quote from: "V8 Bubba"
if you are feelin tough use ya tongue



i bet you have done that on a 9v battery LOL
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Post by: Tank on September 20, 2008, 12:36:12 AM
Quote from: "Dave69"
Quote from: "V8 Bubba"
if you are feelin tough use ya tongue


i bet you have done that on a 9v battery LOL


All the time......what a Buzz!!!!! :wink:  :wink:
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Post by: eastryjeep on September 21, 2008, 06:01:27 PM
Sorry I'm confused here, what do you need to keep your tongue clean for   :?:
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Post by: Tank on September 21, 2008, 08:01:58 PM
Sure i heard something about a pussy....... :lol:  :lol:
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Post by: PtP on October 01, 2008, 01:16:32 PM
I’ve just fitted a new set of Bosch Platinum+4 plugs and whilst doing the last one, No. 6 Cyl. I pulled the plug lead off the distributor cap only to find the terminal had pulled straight out of the cap too! :-)
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Post by: PtP on October 01, 2008, 07:55:09 PM
I’ve fitted a new cap and so far the misfire seems to have gone, :-)

Here is a photo of the problem I had with the cap
(http://http://i82.photobucket.com/albums/j272/mmore514/DSCN4776.jpg)


This shows the only sign of cracking inside the cap too
(http://http://i82.photobucket.com/albums/j272/mmore514/DSCN4789.jpg)


I suspect the cap is the original from 1997 with 60,000 miles on it, but I’m wondering if the burning on the end of the terminal is okay. What do you think?
(http://http://i82.photobucket.com/albums/j272/mmore514/DSCN4786.jpg)
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Post by: Roland on October 01, 2008, 08:01:14 PM
yup that's normal. Did you change the rotor as well :roll:  :?:
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Post by: PtP on October 01, 2008, 08:06:20 PM
Quote from: "Roland"
yup that's normal. Did you change the rotor as well :roll:  :?:

Nope! Should I?
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Post by: TJMart on October 01, 2008, 08:10:11 PM
i would  :-D
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Post by: MOCAJ on October 01, 2008, 08:14:03 PM
and me  :wink:
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Post by: Bishops Finger on October 01, 2008, 08:16:47 PM
Err yes from me as well!
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Post by: PtP on October 01, 2008, 08:23:01 PM
What is there that can go wrong with it?
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Post by: scrw on October 01, 2008, 08:46:54 PM
Quote from: "Bishops Finger"
Err yes from me as well!


 :lol:
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Post by: TJMart on October 01, 2008, 09:01:22 PM
ROFL
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Post by: Bubba on October 01, 2008, 09:02:01 PM
stew can explain
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Post by: scrw on October 01, 2008, 10:09:17 PM
:popcorn:
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Post by: Bishops Finger on October 01, 2008, 10:13:35 PM
Err OK

The rotor is at the top of the distributor

When the engine is turned over it spins and should provide via contacts in the bottom of the distributor cap sparks which in turn via the leads to the spark plugs will spark the fuel in the engine which causes the ignition to make a petrol engine work.......

So if dizzy needs replacing therefore best to do rotor

Do I get a prize?????
 :lol:  :lol:
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Post by: tim_aka_tim on October 01, 2008, 10:18:01 PM
Just as the distributor contacts get corroded from all that arcing, so does the rotor arm. Take out the rotor arm and look for chunks blown out of it, or white/black powder.
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Post by: PtP on October 01, 2008, 10:22:00 PM
I guess I'll just get another one and stick it in. :lol:
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Post by: TJMart on October 01, 2008, 11:01:00 PM
HOORAH  :-D
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Post by: Roland on October 02, 2008, 06:17:45 AM
:shock:
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Post by: PtP on October 02, 2008, 06:16:36 PM
The new rotor is now installed! :roll:

It still runs as sweet as a nut. :-D
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Post by: MOCAJ on October 02, 2008, 06:22:30 PM
keep it as a spare, just in case

they do tend to get as pitted etc as the cap itself, can be cleaned with emery cloth but that just widens the gap slightly

glad your running ok  8-)
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Post by: PtP on January 19, 2009, 06:59:05 PM
After letting the Jeep stand doing nothing for three weeks, it seems like I’ve got my misfire/slight stutter back!

I’ve already changed the plugs, the distributor cap, and the rotor arm and I thought that had solved the problem. Well it seemed to for a while. :roll:

The symptoms are that I can get an occasional misfire either on light throttle or whilst accelerating, but it seems totally random. Also, when you accelerate hard, its as though the engine seems to want more fuel. I regularly jet wash the engine at the same time as the rest of the Jeep and I suspect water might have got into the TPS.

I’m now beginning to think it’s more likely to be the throttle position sensor rather than the crank position sensor. Are the CPS and the TPS expensive items?

Does anyone know what the symptoms are when these two sensors play up?
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Post by: Bishops Finger on January 19, 2009, 10:10:18 PM
It misfires....?

Pete try using it as a DD for a while and see how it copes with real world driving situations....stuff may dry out/and or settle down
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Post by: Panic mechanic! on January 19, 2009, 10:38:34 PM
i hope when you jet wash the engine it was hot....
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Post by: eastryjeep on January 20, 2009, 12:54:10 PM
My vote still goes to a knackered CPS, they only seem to last about 60k to 80k miles at the best of times and if you are regularly pressure washing the engine bay that will only help it on it's way.
It's on the near-side of the bell housing, about an inch back from the rear face of the block and at about the 2 O'clock position when viewed from the front of the engine, when I last changed one they were not all that expensive if you fitted it yourself.
But the exchange rate aint what it used to be either is it Mr Brown ?!

Found this too after a bit of a search, but it shows it's not a job to be afraid of.

(http://http://birtydastardsjeepclub.com/forum/userpix/503_CPS_Image_1.jpg)

And the text to go with the pic!

(http://http://birtydastardsjeepclub.com/forum/userpix/503_CPS_Text_1.jpg)

All rights etc remain the property of Haynes of course.
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Post by: Tank on January 20, 2009, 01:09:55 PM
Quote from: "my other cars a jeep"
keep it as a spare, just in case

they do tend to get as pitted etc as the cap itself, can be cleaned with emery cloth but that just widens the gap slightly

glad your running ok  8-)


Found best thing for cleaning the end is to rub it against a tyre.Doesnt take any off,just removes the crap.Try it,i was suprised too
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Post by: captain cavalier on January 20, 2009, 03:15:00 PM
:imwitstupid:

Used do do mine on the mini that way too once a week

Plus everything else you needed to start the mini.

Folded fag packet inserted between loose points ect
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Post by: PtP on January 20, 2009, 05:30:46 PM
Quote from: "eastryjeep"
My vote still goes to a knackered CPS, they only seem to last about 60k to 80k miles at the best of times .............

Mine’s done around 55k if I recall, so I think it could be on my “To Do” list when the weather warms up.

Thanks everyone for all the input again.

I’ve checked for error codes and there aren’t any. :shock:  and give it a good regular run about and see if this either dries out any damp or throws up an error code.

Does anyone know the approximate cost of the two sensors?


Incidentally, I’ve been reading on another car forum about Jeep TPSs and how they interact with the clockspring and how a badly running engine can be blamed on the TPS whilst the fault is with the clockspring. Have a look here: http://www.obd-codes.com/forums/viewtop ... f=1&t=2468 (http://www.obd-codes.com/forums/viewtopic.php?f=1&t=2468)