disco 1: misfiring/loss of power/high idle

[disco stu]

Hi everyone, i have a 97 Disco 1, 4.0L , auto. 240 000km

When i bought the truck it needed a cat. So on went a new y-pipe.
Shortly after that the idle would be intermittently rough, surging up and down.
Cleaned the AIC, and cleaned the throttle body. Didnt really help much.

So i drove on, since it was not too bad and only intermittent.

Then on the highway a few days later, at cruising speeds of anywhere between 100k/h and up after it was warm... it would intermittently loose power suddenly, for a few seconds, then regain power. (rpms on tach would go down... not tranny slip or anything. i.e. cruising at 2200 rpm.... drops to 2000 rpm for a few seconds, then back up to 2200) As if my foot slipped off the gas pedal... that sort of feeling.

Again, it was intermittent, however that bugged me so i went looking for answers... no EGR on this truck, so maybe the vss?

Before i had time to tinker with it, i was cruising on the highway again a few days later, and it dropped rpm for a few seconds and came back up (like before), then instead of that happening again it started to misfire really bad and loose power... slowing down to 80k/h. It kept doing that for a minute then went away..... cruising again..... back to the small speed drop of 200rpm and back up....

I was able to drive around town and the side roads with little to no problems for a few days after that.

I then installed new plugs and wires, and had a tranny service done (not related, but it was time for one so that was a must regardless)... the old plugs were black around the insulator and whitish on the arm..!?

After that it ran like a CLOCK for the rest of that night. the next day after work i went about an hour cruise on the highway to a friends... after about 25 minutes on the highway the rpm loss here and there.. then about 40 minutes in the misfiring started again... got there eventually..

On the way back it was pretty much driving horrible the hole way... it misfires really bad at about 1800-2200 rpm... and this time it finally threw the Check Engine light.

Since then it has been progressively getting worse, it seems to misfire when accelerating slowly.

If i drop to third or step on it it seems to run more smooth up in the 3000rpm area.... but its not nice to drive the truck like that. So the next day pulled and cleared the codes, and this is what i got:

p1313 bank A misfire - could damage cat

p1314 bank B misfire - could damage cat

p1316 excess emissions misfire

p0300 random/multiple misfire

and misfires on all 8 cylinders (p0301 - p0308)


I changed the plugs again and unplugged the vss, to no change at all.. started misfiring as soon as i got out the driveway. So i replaced the TPS, thinking that it was fouled because when i cleaned in behind it there was what looked like white electrical corrosion.

After i replaced the tps it immediately revved up to 2600rpm at idle on startup! This did NOT happen before... even after warming up it was still at 1700rpm. Slam it in gear and it will grunt down to just over 1000rpm and strain to go against brakes.

Plugged vss back in .. no change... unplugged vss... no change.. changed plugs again (old ones fouled in the same way, all with the same style wear.. none stood out as different)... misfires under accelleration still. When revving the engine in park or neutral it doesnt misfire... or at least loud enough to hear.

Then ran some injector cleaner through the tank... no avail. and put a can of tune-up in a can... what i though would be similar to sea foam, its directed to be put through your vacuum line just the same... however this didnt help either... and also it didnt smoke at all... a little bit of white one time when i revved it... and thats it. so that makes me think that its not the same (or my intake is really clean...).

I have had the suspicion that the problem is the sticky valve 'syndrome' from the beginning... but thought I'd try to exercise the other cheaper possibilities first... So now she sits here waiting to be looked after, while im driving around my rusty tracker


Any help or insight on the issues are greatly appreciated!

disco stu

[apbtpetey]

Originally Posted by disco stu

After i replaced the tps it immediately revved up to 2600rpm at idle on startup! This did NOT happen before... even after warming up it was still at 1700rpm. Slam it in gear and it will grunt down to just over 1000rpm and strain to go against brakes.

I have had the suspicion that the problem is the sticky valve 'syndrome' from the beginning... but thought I'd try to exercise the other cheaper possibilities first... So now she sits here waiting to be looked after, while im driving around my rusty tracker


Any help or insight on the issues are greatly appreciated!

disco stu

For the issue of it revving up so high I would check to make sure you have the right gasket in place for the tps. This happened to me because I was in a rush and ended up not getting the old gasket off. So I had the opld and new one on there when I started it up and had the same high rev issue. I saw my mistake and removed the old gasket and didn't have the high rec issue anymore.

As for the main issues your having it does sound like a sticky valve problem to me.

[disco stu]

Originally Posted by apbtpetey

For the issue of it revving up so high I would check to make sure you have the right gasket in place for the tps. This happened to me because I was in a rush and ended up not getting the old gasket off. So I had the opld and new one on there when I started it up and had the same high rev issue. I saw my mistake and removed the old gasket and didn't have the high rec issue anymore.

As for the main issues your having it does sound like a sticky valve problem to me.

Its the 4.0L engine with the non-adjustable tps... there wasnt any gasket on there, and they dont sell gaskets it seems for the 4.0 L tps.... so i dont know if that is the issue, if yours was a 3.5, 3.9, or 4.2 L then it has a gasket.

On another note, i described the symptoms and what i have done to a local lr guru i just found close to my town. he paused when i mentioned that it all started with weird idling after i put the y-pipe on. he asked if it was aftermarket... which it is. So im going down on friday to his shop to have a chat and check the rover out.

Could the aftermarket y-pipe (cheaper pro-line) be causing too much back pressure and in turn making the engine misfire? like i said one cat was hollow when i bought it... drove it for two weeks 'as bought' and ran perfect. only after the new y-pipe went in did the problems start...

also when i was driving up the hill from town one of the last times i had it out, the last 1ft of tailpiece rusted right off (except for about 1 inch of rust/metal that still had the piece hanging off the clamp) but i noticed an immediate difference when it busted... the misfiring (which was constant) got better and i had a little more power.

thanks for the info on the tps though!

disco stu

[Elemental]

What brand of spark plug are you using?

[disco stu]

Originally Posted by Elemental

What brand of spark plug are you using?

NGK BPMR5EY... i know you wont like that answer haha.

I tried 3 cans of seafoam last night... gas, vac, crankcase. again... not much smoke at all, in fact it only smoked for about 1 minute when i was pouring it in... (took about 5 min to pour in) let sit 25 min and go to drive... no smoke. so it must be fairly clean inside there.

I ran it in third with the revvs up high and when i let off one time and it went back down to 2000 rpm or so it threw the CEL on. so ill get them pulled, most likely the same bunch of misfire codes.

thanks,
stu

[disco stu]

Could the cats be plugged causing it to misfire/backfire out the intake? i mentioned this before... but i also forgot that i ran a tank of 87octane through by mistake one time only... soon after the cats were on. maybe that did it?

[Rovin4life]

check for any air leaks by broken hoses. check fuel pressure,

disconnect the battery for a bit to reset everything including adaptions. That might help a bit, You can change idle with the turn screw but not likely that will help.