Hey guys, wanted to start a new thread for this.


I just recently finished a head gasket job on my 1996 Disco LE.


Since putting it all back together it runs rough every once in a while. Most noticeable at stop lights and under load. Before the head gaskets it ran magically and never sputtered and I never felt any missing going on. It was just loud since the driver side head gasket was failing out the exhaust side on one cylinder.


I didn't change the heads at all when I put the new gaskets in. Didn't touch the valves and didn't have to do any machining to them. I didn't change plugs or wires (I even left the plugs in place when I pulled the heads out). Everything is pretty much the same on the engine except the gaskets (head, intake valley, rocker covers). All of the pushrods went back in the same orientation and order that they were in originally.


So here's a list of things that I am thinking it could be:


1. Plugs (possibly damaged one or more when cleaning the deck surface of the heads?)
2. Plug wires (firing order was re-checked when putting them on)
3. Fuel injectors (all were left in place when the intake manifold came off)
4. Seal between intake manifold and heads (previous person who worked on the engine had silicon sealer on the four corner ports between heads and intake manifold)
5. vacuum lines


Let me know if you think it could be anything else...


I could see it being a bad plug or so since when I was cleaning the driver's side head up, it was probably resting on the tops of the plugs while I was putting some pressure on the head deck surface...


I suppose it could be plug wires - since they are probably routed slightly different than before I did the head gaskets.


I don't see how it would be the fuel injectors - they were not removed and the car ran beautifully before doing the gaskets.


I'm seriously thinking it could be the seal between the intake manifold and the heads being the heads and intake manifold had some sort of silicon sealant on them when I took all of that apart.


I'm thinking it is probably not the vacuum lines being they were just taken off and put back on again. I suppose it could be them though.


Any testing procedures of the above would be appreciated. I'd rather not just start trying to replace things at random.


Thanks again!

 

I've done a bunch of researching threads on this site and someone for a similar problem suggested that maybe the Crank position sensor wire could be put on backwards (reversing the wires and causing a 3 degree difference in its reading). Can anyone verify if that is possible? Can a person put the plug on 180 degrees from its original position?

 

I am happy to report that my problems with rough running engine after doing head gaskets were self-inflicted.

I kept scratching my head, double checking electrical connections, sparkplug wire routings, looking at pictures I'd taken while I was in the process of taking things apart.... I was convinced it was some sort of vacuum leak since some of the time the truck ran as it should. As I was looking at the intake plenum housing I remembered that I put a very thin coat of RTV on the bottom piece and none on the top piece.

So I pulled that top off and cleaned all of what was left of the rtv off and then put a generous bead on both surfaces, bolted it back up and it is once again running nice - no stumbling or stuttering when accellerating! Woohoo!

 

Thanks for posting the follow-up.

 

Well, apparently I'm not done quite yet. The stumble has resurfaced. Pulled the throttle position sensor and put a meter on it and it seems to measure varied resistance in a smooth linear fashion. Haven't ruled that out yet though. Seems like removing the plenum/intake cover and putting it back tends to affect how the car runs. I pulled it off and re-did the RTV and now it seems to be running better, but I don't think it was because of a vacuum leak. I think it must be one of the sensors. May think about putting in a new crankshaft position sensor at some point - that looks like a tricky one to get to though. Had the car up on ramps today and even with that, it seemed like it was going to take some wriggling. Saw the video on a different post about dropping the exhaust - that will probably help. Gonna just drive it for a while and see what happens. The stumbling is driving me nuts tho. After fidgeting with the TPS it does seem to idle a little better and lower rpms. So that's why I am not ruling that out quite yet.

 

Ok, I think I may finally have taken care of my stumbling issue. Here's the story:

For about the last year or year and a half it was making a squeaking noise that I couldn't identify. I held a stethoscope up to each of the moving parts that the belt was on and nothing emitted the squeak. I ended up replacing the belt tension pulley bearing a couple times thinking that was probably it - to no avail. I just kept on driving it. And in the mean time, the exhaust started leaking and it was gradually getting worse. So about 3 weeks ago I took it in and had them weld up a crack in the y-pipe right up by where it connects to the exhaust manifold. The guy gave it back to me and said, "you still have something going on..." because it was puffing out by the exhaust manifold. He thought it was coming from one of the spark plug holes. It still ran great but it was very embarrassingly noisy to drive still.

I pulled the spark plugs on the driver's side out and everything looked fine. I figured it was probably the head gasket based on some youtube videos I'd seen. And that squeak had now turned into a "pfstt pfstt pfstt" sound.

So I ordered the gasket set and head bolts. Performed the 15 hour procedure and figured I was good to go now...







Til I took it for a spin... It seemed to run ok most of the time, but then it seemed like it was occasionally stumbling or missing, but not just on one cylinder - seemed like half the engine would miss. It was especially bad when I was going up a decent sized hill. For the most part it ran ok and seemed that I could get up to about 2000 rpms with no problem, but then after that it would stumble and if I slightly let up on the throttle it then would kick into full power mode but of course you wouldn't be moving very fast.

I tried pulling off the plenum cover and re-RTVing it.



That seemed to help a little but still definitely had a problem. I pulled the throttle position sensor off and tested the ohms on it with a multimeter as I moved it thru its range. That seemed to test out fine - the resistance changed steadily with the movement of the sensor. Then I took readings of the engine coolant temperature sensor when the car was cold and after it was warmed up. That seemed to be in range (340 ohms when warm and 2140 ohms when cold).

I used my hand-pump-vacuum tester on the lines going to the brake master cylinder, the EVAP valve, and the fuel pressure regulator. Each of them held vacuum, so no leaks on any of those.

I cleaned the MAF sensor with MAF cleaner - seemed to run a little better but still stumbled. I even disconnected the MAF sensor and took it for a spin and it ran rougher but still demonstrated the stumbling condition.

I found out that someone must have just removed the bulb from the Check Engine spot on the dash, so I took it up to the auto store and checked to see if there were codes. Boy were there ever. So I decided I would clear the codes and rent the auto store's fuel pressure tester, drive home, check the fuel pressure, return the tool and then check the codes again. The fuel pressure on the rail tested out to be about 34 psi and it held the pressure for a half hour so I figured that was good.



I packed it up and got in the disco drove back to the store (it did its stumbling on the way), returned the fuel pressure test set and used their code checker again. One code was on it. P1316 - apparently that means excessive emissions. So I decided since I was there anyway I would buy a set of spark plugs.

I got home and pulled all my plugs out, keeping them in order of which cylinder they came out of and they all looked pretty uniform and good colored.



Then I decided since I had the plug wires all off the plugs I would pull the coil pack and inspect that. I pulled each of the wires out and looked into each of the tops - that all looked fine.

Then I ran a compression check on all cylinders. Most of them were 137 lbs up to 150 lbs. One of them was at about 128 and then when I checked it again came to 90 lbs so I am a little concerned about that one. I figured that would not have been enough to cause the engine to act like it did though so I decided to keep checking other things.

I put the coilpack back on and attached 4 spark plugs to wires and set them on top of the alternator (where I could see them from the driver's seat while I crank the engine over). As I turned the engine over I could see that they all had nice blue spark on each of them. I did the same thing for the other 4 plugs so I never did end up putting the new plugs in. They will go back to the store.

I decided I would put the plugs back in the engine but in different cylinders that they came out of. Then I started routing the plug wires back to each of the plugs and clipping them in. It seemed that some of them were barely reaching the plug while others had lots of slack in them, so I swapped some wires out to different coils so that they all fit much better. I routed them so that they were not close to the firewall and were not close to the engine and were not close to each other - making sure they were going to the right cylinders (the coilpack has the cylinder number stamped into it that each wire goes to). I clipped them all in and was very happy with how orderly they now looked.

Figuring nothing that I had done would have affected anything at all, I took the disco for a spin and was extremely surprised to find out that it was no longer stumbling.

The car now runs very nicely - like it had before I did the head gasket job. I am thinking the fix for this was probably re-routing the spark plug wires so that they were neatly and efficiently routed to each plug. My guess is that they were either arcing to another wire or to ground somehow when accelerating under load. Either that or I had some of the wires going to the wrong cylinders, but if that were the case I wouldn't think that it would run decently for some of the time but not others...

Anyway, I think I have solved my problem and I hope this might possibly help someone in the future with their frustrating stumbling/misfire problems.

 

Update: it's been a few days now and I have had no problems since the last post. So happy to have a good running disco again!

 

Good to see you got this sorted. BUT are you crazy..... QUIET, The ROVER GODS are listening!!!
You don't want a lightning bolt to come from the sky and fry your poor truck!!!!

 

Haha, I know, right? I thought I had it fixed once, but now after a few days I think for this problem at least it is good.

 

for your solution to this, your plug wires didn’t have any exposed wire right? Where do you think the bad grounding or arcing was occuring?