94 expo 2.4L, auto. Just had the water pump replaced and I don't think that is the problem, but the timing belt was removed during the process and it was placed back where it was found, or so they say. Now, I have a pop noise when I let the motor decelerate around 45 mph. I thought that it was the accerator cable was stucking and releasing with a pop, but the car has to be in gear to have the noise happen. The car runs great except for the " small pop". The noise will be delayed when I am decelerated going faster than 45mph by a second or two. It sounds like a small valve or door closing . nothing loud just something you notice. It even sounds like a single pop while staring the motor, but not when it idles or is out of gear. could the timing be incorrect. While driving the noise sounds like it come from in front of the driver. The noise sounds like a small, small backfire in the injection system. Can anyone help me find the pop? :liebe011:

This post has been edited by top213: Aug 17 2008, 05:08 PM

My guess is that the tensioner bearing was not re-installed correctlly when they replaced the timing belt. This would allow some timing lag of a few degrees duringr acceleration/deaceleration which could cause the engine to knock or 'pop'. have your mechanic remove the top cover plate and inspect the belt tension.

Jim

the noise doesn't sound like a engine knocking noise to me. The noise is a single sound. just one pop as I let off the gas like that is causing it, yet it is delayed when the sped was higher the 45 ? at 55 i can let off the accelerator and it takes a second or two to pop? it is not loud on a scale of 1- 10 it would be a 2. just like you tapped on the top of a empty box.with a finger. just pop!

Detonation will sound when accelerating (knock or ping) due to advanced timing and pop when deacceleration due to timing retarding. My guess is that the slack in the system allows it to retard a few degrees after you release the petal in gear. Have a look because if I'm correct then you will be wearing out the timing belt quickly.

Jim

I just took the car out for another ride. I let the car cool down over night. The pop or click (like a switch closing or opening) doesn't begin until I drive some 20+ miles or so. Does this sound like the timing belt is getting hot enough to expand or create slack in the belt? The mechanic is off today so I have to wait until tomorrow to check it out. Just another thought , is there a switch within the injection system that might stick and click after I get off the pedal? The car runs great. It doesn't miss or studder. It is just this little noise that is driving me crazy.

OK this sounds like something different than the timing belt being slack. I thought you had said it was the engine making the popping noise rather than a click from engine bay. I don't think it will be an injector but could be something like the fuel pump relay clicking off after it has reached full pressure. Or possibly a vacuum selenoid working under de-compression. Best to take back to mechanic and let him figure out.

Sorry, wish I could be more help.

Jim

Jim
Thanks for all you help in this matter. I'll let you know what it is when I found out.
John

Good luck John and keep us posted on the progress.

Jim

how about a wornout bottom and back motor mount which allows the motor to shift more than normal causing the top mount to over extent and pop. I paid to have them replaced 30,000 ago when they rebuilt the front end $1400 but I think they screwed me over and didn't change them out because the front one is worn out and the back is cracking badly. The noise was came after the new "they" lifted the motor to replace the water pump and possible reset the motor in a slightly different location causing a different strain on the old mounts . going to replace the two bad mounts in hope that the noise in the good mount will be silenced.

Good theory. The only thing you really know for certain is that the noise wasn't there before the WP work and was after. The person who did the work would know what he had to remove or replace when doing the job. Could be as simple as a loose motor mount or exhaust bolt.

Jim

Well, you have to remove a motor mount by the timing belt when you are changing the belt, so it is possible that the motor mount wasn't properly re-installed.

Another possible problem is leaving "hidden" balance shaft out of faze 180 degree. Most "non-Mitsu" mechanics make that mistake (they do have a 50/50% chance of getting it right ;)). But he result is vibration, starting at around 2500-3000rpms and not a "clank" as you are describing.

the noise came from inferior motor mounts. both middle mounts were either split or broken. NAPA. Parts what more can I say.

Happy you got sorted and reported back to us.

jim