Mystery Problem

[Steamer's Wake]

Does it back fire when you rev it up under the hood by hand or just when you are driving!

I thought it just did it under load, but it will do it when you rev it up by hand under the hood.

[Steamer's Wake]

I have had experience with fuel injection systems that have the o2 sensors fail and give the computer wrong inputs obout fuel mixture. When they where doing this the fuel wixture became rich which inturn fouled the plugs. Have you unpluged the o2 sensors to see if it makes a difference! just an idea!

We did try disconnecting the o2 sensors with no change.
We also checked everything for vacume leaks.
I think that it backfires less when the engine is cold.
I found that if i get it to kick down into passing gear, the backfiring was not there. So at low rpm light load everyting is fine. About 2200 rpm under load, the problem starts. At high rpm under load no problem.

[Steamer's Wake]

What's next....

We replaced all the spark plugs, taking out the ones that have all of 750 miles on them. We also checked the wires for proper resistance. We changed the temperature sensor for the ecu. No Change. We tried another known good coil. We are running it on a known good ecu. We changed out the distributor cap, with two new ones to make sure we did not have carbon tracking.

I have found that if I push it hard and it kicks down into passing gear the intake backfire is gone until it shifts back up.

[nosxih]

I've had similar probs with my 91 rrc caused by corroded wiring around fuel injectors and temp sensors. Strangely it caused weird thumping noises and loss of power but rarely trip a code.

[Steamer's Wake]

Problem Solved

We found a flat cam. The lobe for number 3 exhaust was almost completely gone. The cam was from Rover's North and was Land Rover Cam. We replaced it with a crane cam that ground for a bit more performance. It runs great now.

[Dan]

Wow! Hard to amagine a hole cam lobe worn down but shure enough that would do it. I am glad that you figured it out! I know how it feels when you finnally get to the bottom of something that you have worked at for so long without getting anywhere!

[phoenix]

glad to read you got it, remember my sugestion of using an oscilloscope? that would have given you an orientation of a bad valve or cillinder not firing correctly not nescesarily a misfire.

[Steamer's Wake]

Thanks for all the tips. The oscilloscope
was a good tip I just didn’t have access to one. I kept looking for one that we could use. I agree that it would have been great to use one early. I am also glad to have solved the problem. The performance cam we put in is great no noticeable idle issues and it seems to rev and run better. We live where there are a lot of mountain passes and I like the cam. Now on to my blown transmission cooler line….