1997 Landrover Discovery - 4.0L Skips 2.5 sec FIXED

[jbadenoch]

Hey everyone. I have a 1997 Landrover discovery se7, 4.0 8cyl here at the shop. came in a few months ago with engine misfire, plugs were very worn. Replaced plugs and it ran great for a month, came back with int skip. Changed plugs again figuring defect and it ran great for a month. came back with an int skip again, did plugs again, had no time to play, and ran great again. Now its back and am not gonna bandaid again.

Our modis has no landrover program till end of week so I don't have much to work with. have changed all 4 ign coils and no help. have changed ign wires and no help. had a p1313, and p1316 bk "A" poss cat damage. When cold it runs great for 15-20 miles then skips on and off with precise timing, skips for 2.5 sec then great for 2.5 sec, back and forth. Throttle position or eng load not a factor, can even feel it when decelerating. When ideling or brake torque, will not misfire so can't isolate which cyl only bank "A" .

Hoping one of you magicians can offer some help.

[steven kiser]

sounds like a bad cam or crank sensor

[jbadenoch]

was thinking of trying it any way. I'll let ya know as soon as I do.

[jbadenoch]

good tuesday morning to ya'll. I see not too many bites on this one. going to scope crank sensor and cam sensor today, i'll let ya know.

[jbadenoch]

crank and cam sensors scoped ok. changed anyway, no help.

[Tim Martin]

crank and cam sensors scoped ok. changed anyway, no help.

I'm not surprised. My first thought as I read the initial post was possibly faulty ignition wires, possible ground issue, or possibly a PCM issue. Even possibly a lean running engine that overworks the secondary ignition system. What are fuel trim values? Also, what is the voltage coming to the ignition coil(s)? That needs to be battery voltage. But beings this is a firing setup where two plugs fire at the same time, my gut feeling is that in the secondary ignition is where the problem is.

[jbadenoch]

voltage to coils is equal to battery voltage. s fuel trim from +24 - neg 3 bank 1. bk 2 almost identical even when misfiring. LT both banks hanging around +3 even when misfiring. ???? fuel pressure 30 psi at idle, 40 psi on accel. changed plugs again at end of day and this time it didn't fix like the last 3 times? Landrover update for modis coming friday, hopefully obd2 side of pcm info will help

[steven kiser]

a few things here, the repetitive skip pattern has me a scratching my head a bit. the single biggest issue i've had with these is exhaust valve's sticking. land rover has a redesigned exhaust valve but i replace the heads. there are a few ignition issues that cause intermittent skips but you've seemed to have covered them. can you identify which cylinders are causing the misfire by the condition of the plugs? there is a tech bulletin that instructs you on attaching and reading a vac gauge to check for a valve issue. the top ends of these engines are crapolla. good luck.

[jbadenoch]

I appreciate some of the insight on this **** box, but it's going to the dealer, (last place i want to send anyone) and the customer will let us know what the fix was then I'll post it for ya. Once again, thanks for the insight.

[steven kiser]

sometimes it's best to send it to the dealer. unfortunately the dealer is going to throw you under the bus.

[jbadenoch]

as long as its not the short bus.

[fortknoxx]

as long as its not the short bus.

put your helmet on lil buddy

[timbre4]

http://www.acidplanet.com/components/em ... 1430&T=496

[jbadenoch]

sent this one to dealer and have not heard back about what the fix was. thanks to all who helped. Bob in sc

[jbadenoch]

Dealer doesnt know either, throwing parts at it

[liljoe]

If they find the problem I would like to know what it was, I just bought a nice forrest green one of these, seems like a neat truck....

[steven kiser]

i don't know why i didn't hit on this at the beginning but are you using anti seize on the plug? i've run into issues like this before. not on this particular vehicle, but on more than just one or two. the anti seize will force loss of ground. i'm still a bit confused about the consistency of the skip. with patterns like this i usually find it's hitting during an emission test. if the fuel lines were somehow crossed and it was calling for an evap test raw gas may being introduced into the system and after a while will knock out a plug. there may be more than one contributing factor causing the end result. i would look into the anti seize as well as possibly shutting down all vac feeds from or to the engine and see what happens. watch the scanner while this is happening. see if any valve is being switched as well as the timing or high knock signal. on rereading the initial post the issue was a constant skip now we have a times intermittent. are we possibly getting a transmission shutter confused as a skip. i know it's a stretch and i'm not questioning anyone's ability but i've assumed that the issue at hand was the one from before and have been wrong. what happens if you drive it in third gear avoiding the converter trying to lock up. again, just throwing something out there to look at. sometimes this kicks me out of a locked thought process and i see it at a different angle.

[jbadenoch]

lil joe, i'll certainly let you know prognosis as soon as i hear. steve, definately not trans related but you've got me thinking on the comp running emission tests. I only wish the vehicle was still here, we now have lr program for modis. only thing is changing plugs fixes problem for about a month? I suppose excess fuel could be slowly degrading plug. Really hope the dealer can definitively say which part they are tossing at it actually fixes it. yall have a great weekend, i'll keep you up to date. Bob in sc

[jbadenoch]

rth. trying to fix time stamp, succeded. rth was just to post and see

[liljoe]

rth

????