I have had an engine issue on my 94' ever since I bought the truck a year ago. When I drive around town under 35 it runs fairly normal, when on the freeway or over 35 it develops a tick. Also on the freeway it will run as though it is only firing on 6 cylinders and has lost power. I have flushed it many times with ATF and have tried about every oil weight out there looking for something to solve the issue. I have not removed the valve covers yet but looking down through the oil fill in the cover I can see it has some dark caked on oil. While running I do not see much of an oil flow around the rockers and valve springs. I am concerned that I am not getting enough oil flow up top, especially at higher rpms. I have done an oil pressure test at the sensor it is fine. I also just ordered new o2 sensors just in case it is fooling the computer to thinking it needs to alter the ignition timing or something, but I am not sure that it can actually happen that way.

I am thinking I should drop the pan, clean the oil pick up and I am afraid to say it but I may need some head work if the vanes are clogged, since a flush wont do it. If you have any other suggestions please let me know. I would prefer not tearing into the engine. Thanks!

 

How many miles? A couple of things come to mind. The first is weak valve springs and the second is bad plugs and/or wires. When was the last time they were replaced?

 

I know plugs and wires were replaced about 2 years ago, I now have about 148K and I bought it with 136K. I guess that is a place to look, I have already looked it over for the wires grounding out somewhere and could not find anything. I did not think of the valave springs at all so that could be a culprit. It is just odd that it comes and goes and os not a constant issue like when it is driving at lower speeds.

Any body know where I can get valve springs and maybe some lifters since I would be replacing the springs? Any other suggestions is greatly appreciated.

 

I would be more inclined to think aburned valve. With that mileage and it being a 94, carbon builds up on the Exh valves and burns them out. If you are pulling the heads, have them fully checked out before you buy new lifters/springs.

www.roverparts.com has good parts.

 

Since it happens only at higher RPMs, valve float seems like a more likely candidate to me. I've seen it in high mileage engines where the valve springs are weak and cannot fully overcome the resistance of the valve in the guides at higher RPMs- particularly if the stems are carboned up.

A burnt valve is a bit of a misnomer. Valves can overheat and distort, causing a poor seal on the seat and letting combustion gases escape and making the valve cooling problem worse. Eventually, a valve can start to lose chunks of its head and the leaking gets much worse, along with a reduction in power output. This would show symptoms at any RPM.

As engines wear, the valvetrain components cannot react as quickly as they once could to the normal open/close cycles, and their duration of lift gets longer and longer, while as the cam lobe wears, the height of lift gets less and less. This is normally experienced by the owner as a gradual decline in performance over time. Eventually, the valve gear can no longer do it's job and a regular miss at high RPMs develops on one or more cylinders. the symptoms are similar for a sticking valve. If this is what's happeneing to rob, then it's time to overhaul the heads. Otherwise, I'd be inclined to look for an electrical root cause in the ignition system.

Dave

 

This sounds to be more of what may be happening. I have checked all the electrical and have no change or saw anything that would cause me to be suspicious. I may pull the heads and take them to get rebuilt, or maybe just buy form Roverlandparts or something like that. Which one would you reccomend that I do? I am afraid if I took the heads somewhere local they could be there for a while since everyone looks at the truck and says "oh, dealer only".

Thanks for the great help.

 

http://www.robisonservice.com/servic...er_advice1.asp

Read through this, it will give you some insight.

 

Thanks for the help!

 

Let us know when you get it figured out.

 

OK, I have been trying to still figure this one out. In an effoert to try to avoid having to redo the heads I though a good induction cleaning would be in store. I did the Seafoam induction cleaning as per what I have found here and how Disco Mike said to so it. I also put some in the fuel along with a new fuel filter. I also put in new O2 sensors. It ran like crap afterwards and then sent searching other places for issues. Mike said to do a compression test and so I did. When I took out the fairly new plugs I noticed three that had a ton of carbon build up on them.

COmpression came out between 160-165 per cylinder. I replaced all the plugs and wires. I had a bad connection at the cap from the coil that I fixed with a new cap rotorand lead wire. Started it up and it ran much better, thought I was in the clear, still had valve noise but it calmed down a little. Took it on the freeway to check it all is OK and then it got even worse.

It feels as though it is only running on 4 cylinders. I can smell a bunch of fuel in the exhaust and there is no power when it comes to climbing a hill or even getting on the freeway. I figure I better take off the oil pan and check the pick up tube of the oil pump, eventhough I have had an oil pressure check that turned out to be normal.

I am now thinking that my heads are FUBAR'd so much that oil is not getting up there and I have frozen valves thus causing the massive headache the truck is becoming. If anyone thinks I am off base here let me know I am about to run this into a wall.