Engine Noise after Rebuild

OK, this is a 90 Renix with a newly rebuilt engine, 3000 miles ago.

After rebuilding the engine at a GOOD shop, we are getting a fairly loud ticking sound around the #2 cylinder. Compression is good, valve train looks fine.

I suspect what we are hearing is the old 200K mile fuel injectors misfiring. Can someone confirm what a "bad" injector sounds like? I've told my cheap-ass friend to change 'em, but I need you're help convincing him that this is a DAMN good idea.

He needs a new Cat too, but I'll save that battle for another day.

Anything else we should look at? Its too high for rod noise, and I don't think a piston is burned (car is not overheating and emissions are spot-on).

You could either get hold of a mechanic's stethoscope or use a length of rubber pipe and listen over the valve cover to find out if the ticking is coming from the valvetrain. The same method could be used to listen over the injectors.

Dr. Dyno said:

You could either get hold of a mechanic's stethoscope or use a length of rubber pipe and listen over the valve cover to find out if the ticking is coming from the valvetrain. The same method could be used to listen over the injectors.

Click to expand...

Yeah, been there, done that. We had a auto tech professor from DeAnza college come over and check it out. Said probably not valves (we pulled the cover) and not likely burnt piston. I don't think he steth'd the injectors though....

Had a similar problem after rebuilding the 4.0L in my '88. Several mechanics told me it had to be a bad (new) lifter. It sounded like the noise was coming from the head, so that made some sense. I had even used a mechx stethoscope, but man are those noises hard to pin point- especially with all the other racket going on under the hood. Anyway, it turned out that the noise was caused by a warped flywheel. It would make a ticking noise in time with the engine (obviously). Had it swapped out with a junkyard replacement.

Well, piece-by-piece, I wish that was the case.

We spent some time last night with the beast and here's what we found:

#1 sparkplug tip was dark grey and insulator was cracked, all others had nice toasty tips.

#1 cylinder compression was 90/120 vs. average of 90/140-145 for other cyliners (1st puff/highest reading on cold engine with all plugs pulled).

I'm suspecting #1 fuel injector was shooting a stream rather than a spray pattern and washed the cyliner wall. That's my worst fear.

Forgot to check cylinder head bolt torque so that, along with new spark plug and injector are next, followed by another compression check.

I'm hoping we didn't fawk up the cylinder or piston. When I shine a light down thruough the sparkplug hole the piston top looks like the rest.

Oh yeah, did I mention we have but 4000 miles on this puppy.

Just un-plug what you beleve to be the bad injector.

langer1 said:

Just un-plug what you beleve to be the bad injector.

Click to expand...

So, what you're saying is let #1 cyliner "free-wheel" to see if noise goes away?

I suppose it could be something as simple as a bad plug and head bolts, but I kinda doubt it :-(. These injectors had 225K miles on em.

Nevada City Sparky said:

So, what you're saying is let #1 cyliner "free-wheel" to see if noise goes away?

I suppose it could be something as simple as a bad plug and head bolts, but I kinda doubt it :-(. These injectors had 225K miles on em.

Click to expand...

Better yet nove it to #6 and see if the noise moves with it. I bet it don't.

UPDATE:
First of all, I ordered my buddy his birthday and Christmas present (injectors)

Second, he retorqued head bolts (1/4 turn it took) and we are back to 150 lbs. in the first cylinder. We may just save this one yet. We'll replace the plug and injectors and see what happens.