96 Roadmaster stumble

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96 Roadmaster stumble

Post by kevm14 » Sun Jun 23, 2019 7:57 pm

I previously mentioned from day one that there was a very light tip in stumble which is typical of LT1s with pending EGR issues. Well today I power washed some stuff including the Roadmaster and I wanted to drive it a little. Upon tipping into the throttle to leave the driveway (it had been idling the whole time I washed it so it was fully warmed up), it stumbled pretty massively. It did it again and again. It would rev clean and idle fine but at part throttle it was actually pretty bad. It revs clean in park and also winds out clean. It's the part throttle that is the issue.

I got my scan tool and sure enough, massively negative fuel trims during the issue. I played around with it some more and eventually drove to the gas station to get some fresh 87. It was better on the way back but still doing it. The trims were better, too. I am 99% sure it needs an EGR valve. I could confirm with my Tech 2, that it stumbles when EGR is commanded but I should just order one - I'm familiar enough with this. Do I get the regular one or the M6 F-body valve which was seen as an upgrade on the B-bodies when aftermarket exhaust was used. This car has stock exhaust but I may change that. And I assume the M6 valve would work fine with stock exhaust as well...

EGR is also symptomatic of the fact that it absolutely felt like it wanted to die but never actually did. That is a classic EGR issue, too. When the manifold pressure completely goes away as it would when it is about to stall, the EGR closes and sort of self-prevents the stall.

To be continued.

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Re: 96 Roadmaster stumble

Post by kevm14 » Sun Jun 23, 2019 8:03 pm

RockAuto lists the same AC Delco EGR valve for the Roadmaster and automatic F-body as I expected.

ACDELCO 2145084 {#17113382, 19210659} GM Original Equipment Info
Except Leaded Fuel Emission Export (NM8); PROD 17092172
ACDELCO 2145084 {#17113382, 19210659} GM Original Equipment Info
Trans. code 4L60-E; Except Leaded Fuel Emission Export (NM8); PROD 17092172; 4 speed Automatic trans.

Then the manual one which is $68:
ACDELCO 2145083 {#17113381, 19210658} GM Original Equipment Info
Trans. code MM6; Except Leaded Fuel Emission Export (NM8); PROD 17092160; 6 speed Manual trans.

Maybe I should just get stock and deal with it if and when I do an exhaust. Just didn't want to pay twice and if the M6 one works fine with a stock automatic car then why not upgrade it...

I'll think about it for a bit and then order it with the A/C clutch since I haven't ordered that yet either.

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Re: 96 Roadmaster stumble

Post by kevm14 » Mon Jun 24, 2019 11:53 am

https://www.impalassforum.com/vBulletin ... sue-2.html
Lots of threads on the subject if you just search "f-body EGR", here is just one....


Back when I replaced mine I just went onto one of the parts sites and selected an EGR for a 95 Camaro (f-body) with LT1 and manual trans. Be sure to replace the Solenoid (not that expensive) while you're there and inspect closely the Vacuum lines.

There is most likely more details on the benefit of this mod and why listed throughout the numerous threads. I did find some detail here from the QaloSS Handbook but this is a dated document. Here is the cut n paste info from there on this mod.....

EGR Valve Replacement
One of the common repairs to the B-body LT1. It will cause hesitation, stumble, and hurt
gas mileage. It’s an easy fix but a little pricey and annoying.
Get a new one or get the 6-speed EGR valve from the F-Body LT1. They tend to last longer
and are the same price anyway. So buy it. Go ahead and get the solenoid as well, they’re not that
much and it’s good to replace it while you’re back there.
1. The valve and solenoid are located on the back of the
engine on the driver’s side. The valve looks like the one to
the right.
2. It is held on by two bolts and connecting by hoses to the
solenoid. The solenoid is connected by bracket to the engine
that is secured a bolt.
3. Be sure to make note of how the hoses are connected while removing it.
4. Remove the old gasket from the valve and engine, and replace it with the new one and install in
the reverse order.
EGR Campaign Letter:
If you have a 1996 with less than 100,000 miles on it and fewer than 10 years old, you may be
eligible for a free replacement. Read the campaign letter at this link:
Leaning toward the 6-speed one. Wasn't planning on doing the solenoid though.

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Re: 96 Roadmaster stumble

Post by Adam » Mon Jun 24, 2019 8:26 pm

I had that issue on the Fleetwood. Then it set an EGR code. I replaced it with the standard Delco one. So far so good, even with "performance" mufflers. Mine isn't OBD-II, though...

Also didn't replace the solenoid. I have a spare on the Caprice engine, unless Ed borrowed it already.

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Re: 96 Roadmaster stumble

Post by kevm14 » Tue Jun 25, 2019 6:20 am

It's not an OBD-II thing in this case. OBD-I cars, such as my Caprice, had at least one EGR code/diagnostic.

I am ordering the 6-speed one.

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Re: 96 Roadmaster stumble

Post by kevm14 » Sun Jun 30, 2019 2:20 pm

Installed new EGR valve. Fixed.

Old valve. Stamped GM/Rochester and made in the USA. Doubt it is the original though. But it is probably an older OEM replacement.
New valve. Made in China. Part number on the box didn't exactly match the EGR but it looks right to me.
It's funny. If you are used to old cars, I guess this would have been considered a bit of a pain. Compared to some of the stuff I am used to working on lately, this was hardly difficult, even though it is at the back of the intake manifold, under the cowl.

Fuel trims seem to be back to normal and drivability is restored. It still has some softness on heavy throttle snap and I am 99% sure that is in the tune as burst knock. It drives very well overall.

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