SureTrack Community Fix: It’s all in the Intake

After replacing an engine twice in the same vehicle and still having strange mechanical and performance issues, you’d be pulling your hair out. SureTrack community member mdwoods1122 had a Chevrolet Equinox in their shop that came in with a blown engine. They replaced it twice and both times it wouldn’t run right and seemed like it was blown again. They posed the question to the community, and with the help of fellow community members ericsautomotive, Richard_C and others, they were able to resolve the issue quickly.

The following Community Fix summarizes the interaction between members of the community that led to the solution.

Vehicle
2014 Chevrolet Equinox LS 2.4L

Title
Engine noise and bucking during test drive, replaced intake manifold.

Complaint
After engine replacement, makes noises and bucks and dies during test drives.

Diagnostic Steps Performed/Parts Replaced
Customer bought vehicle at auction, swears it drove there, now engine is seized. After tear down, found engine threw a rod which was holding engine from turning. Replaced engine with customer supplied remanufactured engine. Engine runs smooth at idle with no issues. Tech drove vehicle and made it halfway around block, engine started misfiring, bucking etc and died, would not restart. When cranking, sounds like something came apart inside engine. Towed back to shop, after cooling off engine starts and runs fine, no noise. Attempted test drive and made it one block and engine stalled out. Cranking engine and again sounds like something came apart in engine. Let it cool and attempted to drive back to shop, engine missing, bucking, has no power or vacuum to brakes, knocking. Check engine light flashing, power reduced message.

Scan test shows misfire on #1 cylinder, compression test shows #1 cyl has 0 psi compression. Inspector came out and scoped inside and said coolant entering head so we replaced engine again. Vehicle starts and runs smooth, test drive shows after driving engine starts missing, this time on all 4 cylinders, bucking and jerking, sounds like something came apart in engine. Almost did not make it back, codes p0171, p2096, cleared then p0506, p0300. Exhaust back pressure test checks good, fuel pressure checks good, fuel quality checks good, plugs gas fouled, replaced, inspector came out and said we were crazy it runs fine then he test drove and almost did not make it back. Misfires on all 4 cylinders again, he threw his hands up and said he had no clue, never seen it, I can run engine in shop for hours without issue, thinking something broken off in cat/exhaust.

Just wondering if anyone has seen this issue after engine replacement. Symptoms can be reproduced but only when driving. Don’t really want to risk engine damage again when this one seems to run fine in shop. And sounds great too. Revving engine in shop shows no problem either, only after trying to drive down the road. Could the noise I’m hearing that sounds like inside engine when problem occurs actually be inside cat? I guess I’m pulling it off and checking, let you know.

Cause
Thanks for all the comments, sometimes we just have to rack our own brains/memory to find the problem, I was not the one who replaced the engines, I only got it after the second engine and having the same problem, the original engine was seized due to catastrophic failure, which jogged my memory about an old TSB from GM concerning intake replacement due to catastrophic engine failure, which made me look inside intake where I found all kinds of debris from the original engine, large chunks of piston etc. Not sure why the original tech didn’t hear it or see it during transfer both times, but anything can happen with complete engine installs.

Correction
Replaced intake manifold with new unit. Vehicle performs as it should on road test.