Shutter, hesitation mystery solved. LT1 Chevy 5.7 liter engine.

[adallak]

So, after 17,000 miles and three years the cause of that annoying shutter/hiccup I experienced from time to time usually around 43-44 MPH going up a hill and trying to keep momentum by depressing gas pedal has been determined and eliminated!

I was told that a faulty EGR valve could be among many other possibilities causing the shutter. Shortly after buying the car three years ago, I checked the original EGR valve right on the engine and the diaphragm appeared to be shot. Let me stress that there was no EGR related code despite obviously shot valve. I have replaced that defective part with used but what seemed to be good EGR valve with matching GM part number. Nothing changed.

Just like many of us, I have replaced spark plugs, wires (argh!), checked TPS and many other sensors. Nothing changed, teh shutter was still there.

About a year ago EGR code 32 started showing up intermittently. For some reason, I was sure it was rather electrical problem since the valve was clean as whistle, plunger moved smoothly and the diaphragm was intact. I WAS WRONG!!!

Finally, saw new ACDelco EGR valve on Amazon for $47 shipped. Bought one. The part is made in China and assembled in Canada. Installed it in ten minutes and took car for about one hour drive to see. Wow... N O S H U T T E R !!!! I have created conditions when a shutter would definitely happen some 15 -20 times. Nothing, no shutter!

So, 1994-1996 Fleetwood folks with shutter hesitation problem, please take that stupid part seriously. It is a finely balanced pretty sensitive part. It may look okay, but it does not mean it works properly. See, it took many years before 32 code was set. Even a valve with shot diaphragm did not set any code. So, if you have shutter, replace that part with known good one. It is a 10 minute work on these engines.

A side not not a rant. What's the use of onboard diagnostics if an EGR -related trouble code never showed up while the diaphragm of the valve was shot for years? It is particularly frustrating if one takes into account that these LT1 engines are extremely sensitive to even minor ignition problems, vacuum leaks, exhaust leaks, etc. I might be wrong but I think GM engineers should have done a better job tuning these engines.

[KHE]

Another thing that will cause hesitation is plugged EGR passages in the intake manifold.

I replaced the intake manifold gaskets on my '93 Fleetwood about a year ago - it was leaking coolant where the intahe joined the passenger side head. I had a hesitation for several years - especially during hot weather. When I removed the intake, the EGR passages were completely plugged up. Since the intake was off, I completely cleaned the EGR passages and upon reassembly, there was no more hesitation.

[adallak]

Another thing that will cause hesitation is plugged EGR passages in the intake manifold.

I replaced the intake manifold gaskets on my '93 Fleetwood about a year ago - it was leaking coolant where the intahe joined the passenger side head. I had a hesitation for several years - especially during hot weather. When I removed the intake, the EGR passages were completely plugged up. Since the intake was off, I completely cleaned the EGR passages and upon reassembly, there was no more hesitation.

KHE, passages are relatively easy to check by pressing the EGR valve diaphragm with fingers while engine is cold and in park. If nothing changes, teh passages are plugged. If RPM drops because of huge vacuum leak to the point engine is about to stall, the passages are free.

Intake gaskets leak on LT1 engines as well. Mine were replaced before I bought the car.

[KHE]

I've lifted up on the EGR diaphram plunger and the engine stalled yet I still had the hesitation when hot. When I had the intake off, the EGR passages were completely coked shut. I spent some time rodding them out. The hesitation was gone after I reassembled everything.

I have no complaints on the intake manifold gaskets on my car - they lasted 18-1/2 years and almost 143,000 miles. While I had the intake off, I had it jet washed to clean it up and then repainted it with high temp. flat back so it looked new. Big difference in appearance.

[joeb]

My egr would stick open occasionally. I put on a used one and problem is fixed. Tried to clean it. No good. Found 2-3 at boneyard. One from identical yr car looked dirty on the outside. Another looked brand new but was a few yrs off. I went with same yr part and it works. So, sometimes u get lucky.

[Logan]

As nice as the on-board diagnostics are..it cannot replace the need for a scan tool in the hands of a driveability technician.

The older GM car were much more forgiving with the SES lamp vs. OBDII vehicles. Latter OBDII cars it becomes a 'must fix' situation. You also do not want to create a situation where the SES lamp is always coming on and cant be fixed.

You also have to guess what Joe Public is going to do....wrong spark plugs...wrong EGR valves. Have seen 'diagnostic' BB's in EGR vacuum lines. Have seen aftermarket 4 inch exhaust systems create a false code 32 due to a lack of exhaust back-pressure.