Engine cuts out at idle

[andy d]

Evening all.
I have a small problem with my 1956 GMC. But as it has a 1976 400cid engine with a Rochester two barrel carb, I thought it made more sense to post on the later model board.
I recently replaced the accelerator pump, and the engine was running nicely.
Last week I took the valve covers off to repaint them.
Since placing them back on, the engine refuses to idle. It accelerates OK, but just cuts out at idle.
The only item that was removed, other than the valve covers was the EGR valve. I had to remove it to get the valve cover off. It was put back in without any fuss.
The vacuum hoses have all been checked, and nothing seems out of place.
Before I remove the carburettor and start rebuilding, I thought it would be best to seek advice from people smarter than me.

['68OrangeSunshine]

Vacuum leak[s].

[andy d]

Originally Posted by '68OrangeSunshine

Vacuum leak[s].

Could be a good call. Might try checking them individually to see.

['68OrangeSunshine]

Originally Posted by andy d

Could be a good call. Might try checking them individually to see.

With the engine warm and idling, take a can of Carb spray cleaner and spray short bursts at places around the intake, under the carb etc. If the volatile MEK and other substances in the carb spray are sucked into the air-fuel mixture, the idle will stumble or surge from the variation in combustables and give you an indication where the leak is.
BTW, this site has a special Engine and Drivetrain forum.

A 2 barrel on a 400? Seems counterproductive. But then gas isn't a quarter a gallon [for premium] anymore.

[andy d]

Originally Posted by '68OrangeSunshine

With the engine warm and idling, spray short bursts at places around the intake, under the carb etc. If the volatile MEK and other substances in the carb spray are sucked into the air-fuel mixture, the idle will stumble or surge from the variation in combustables and give you an indication where the leak is.
BTW, this site has a special Engine and Drivetrain forum.

A 2 barrel on a 400? Seems counterproductive. But then gas isn't a quarter a gallon [for premium] anymore.

Fantastic. Great advice 68.
And I wish fuel was that cheap. frightening how much the truck drinks.

['68OrangeSunshine]

Originally Posted by andy d

Fantastic. Great advice 68.
And I wish fuel was that cheap. frightening how much the truck drinks.

That's just an old hotrodder's Injun trick.

My Dad had Jag Mark VIII Saloon car back in the day ['60s]. That car would pass anything on the road except a Jaguar Repair Station.

I used to run a '67 K/10 Suburban [4x4] with a TH350 tranny and a 454 BBC, now that was one gas-guzzlin' beast. 6 City, 8 Highway mpg.

Cheers, Mate,
hope you catch your gremlin.

[andy d]

I ran through the suggestions as above, but couldn't find anything out of the ordinary.
Mind you it was hard going trying to keep the engine running whilst spraying the carb cleaner. handy little piece of steel bar did the trick.
but no luck finding the problem.
So I went back to looking at the EGR valve.
I took it off the motor and checked to see if the diaphragm was working. Nope, it does not work at all. So it looks like the EGR is u/s.
Ordered a new one up, and will hopefully resolve the problem.
Thanks again for the help.
I really appreciate it.
Especially since that are a few tips and techniques that I am learning.

[geezer#99]

Why do you need an egr valve?

[andy d]

Originally Posted by geezer#99

Why do you need an egr valve?

Well that is indeed a good question.
Making up a blank pff plate might be an easier fix, but I suppose there is a part of me that likes to keep the engine as close to its original setup as possible.
Less opportunity for me to make a hash of things

[geezer#99]

You got a pic of this motor?

['68OrangeSunshine]

Andy, I don't know what [if any] are the emissions requirements in the UK, but for a 1956 pickup, I doubt it's much.
In my humble opinion, you're going in the wrong direction, as far as performance. If you're chasing all the Mid-'70s emissions patches that GM did to make a good, powerful well-breathing engine into a politically-correct enemic Rube Goldberg you'll get poor results.
You've hit on the '67-'72 Forum by chance, so later vintage tuning with what we feel are unneccessary performance inhibiting modifications, AIR, TCS, EGR etc. are foreign to us.

It's a '56 GMC -- make it a hot rod by cleaning off all the emissions impediments -- go back to a basic 400 [SBC?]. Put on an aluminum intake for a 4 barrel carb, add your carb of choice: Quadrajet, Edelbrock, Holley -- something between 600 -700 CFM.
Mount some headers to keep up with the new advanced A/F input. Dual exhaust with an H-pipe crossover will help low end torque. Muffler choice is up to you, but unless you're 17 and don't care if the cops get interested in chasing you, I'd stay away from glass packs.
PCV and HEI are good innovations, I'd keep them.

I know I've just spent about $2000 USD in imaginary money and I can't imagine that in GBP plus VAT and S&H, but dreams are free, if nothing else.

[andy d]

Originally Posted by geezer#99

You got a pic of this motor?

Not the best image, and the valve covers have been painted.

[andy d]

Originally Posted by '68OrangeSunshine

Andy, I don't know what [if any] are the emissions requirements in the UK, but for a 1956 pickup, I doubt it's much.
In my humble opinion, you're going in the wrong direction, as far as performance. If you're chasing all the Mid-'70s emissions patches that GM did to make a good, powerful well-breathing engine into a politically-correct enemic Rube Goldberg you'll get poor results.
You've hit on the '67-'72 Forum by chance, so later vintage tuning with what we feel are unneccessary performance inhibiting modifications, AIR, TCS, EGR etc. are foreign to us.

It's a '56 GMC -- make it a hot rod by cleaning off all the emissions impediments -- go back to a basic 400 [SBC?]. Put on an aluminum intake for a 4 barrel carb, add your carb of choice: Quadrajet, Edelbrock, Holley -- something between 600 -700 CFM.
Mount some headers to keep up with the new advanced A/F input. Dual exhaust with an H-pipe crossover will help low end torque. Muffler choice is up to you, but unless you're 17 and don't care if the cops get interested in chasing you, I'd stay away from glass packs.
PCV and HEI are good innovations, I'd keep them.

I know I've just spent about $2000 USD in imaginary money and I can't imagine that in GBP plus VAT and S&H, but dreams are free, if nothing else.

To be honest the emissions regs for vehicles of this age are prettty non existent. So that isnt anything to be worried about.
I think you are right about the emissions stuff. They just add clutter to the engine bay.
I am more used to the Italian engines, including the bizarre SPICA injection system. A lot of the emissions stuff just baffles me.

['68OrangeSunshine]

Originally Posted by andy d

To be honest the emissions regs for vehicles of this age are prettty non existent. So that isnt anything to be worried about.
I think you are right about the emissions stuff. They just add clutter to the engine bay.
I am more used to the Italian engines, including the bizarre SPICA injection system. A lot of the emissions stuff just baffles me.

Well, yeah. Get it running for now, even if a new EGR gadget makes the right voodoo.
Then " Save up your Nickels and Save up your Dimes" [with apologies to the Beach Boys] until you can grab some of the afore-mentioned speedshop goodies.
How about a pic of the whole truck? I'll bet it's a stepside ['Fenderside' in GMC speak] and probably was produced with an L6, either 270 CuIn GMC or 235 or 261 Chevy. I'll make a further guess that it's a USAF surplus CUCV. If so, is it still dull blue?

I used to drive a <<feldgrau>> '61 Mercedes 190B with [an almost] 2L L4 and 4-on-the- column Mauser Bolt Action gearshift. Loved that car. Ran the hell out of it in college til I blew it up on a SoCal freeway. Then I bought a '68 C/10 Chevy Stepside w/292 L6 in Omaha Orange. I was done with imports. I wanted a vehicle with ready parts access, simple instructions in my native language, and extreme ease of maintenance. Still driving it 43 years later.

From your pic, looks like the anti-dieseling solenoid is not connected.

[68gmsee]

I agree with what 68OrangeSunshine said about the engine emission add-ons restricting the performance. I've had two 350 engines of the same era, a 75 and a 77. I quickly got rid of all the emissions stuff and went with the basics: HEI, PVC, quadrajet, blocked off the egr and added rams horn dual exhaust manifolds.

[andy d]

Originally Posted by '68OrangeSunshine

Well, yeah. Get it running for now, even if a new EGR gadget makes the right voodoo.
Then " Save up your Nickels and Save up your Dimes" [with apologies to the Beach Boys] until you can grab some of the afore-mentioned speedshop goodies.
How about a pic of the whole truck? I'll bet it's a stepside ['Fenderside' in GMC speak] and probably was produced with an L6, either 270 CuIn GMC or 235 or 261 Chevy. I'll make a further guess that it's a USAF surplus CUCV. If so, is it still dull blue?

I used to drive a <<feldgrau>> '61 Mercedes 190B with [an almost] 2L L4 and 4-on-the- column Mauser Bolt Action gearshift. Loved that car. Ran the hell out of it in college til I blew it up on a SoCal freeway. Then I bought a '68 C/10 Chevy Stepside w/292 L6 in Omaha Orange. I was done with imports. I wanted a vehicle with ready parts access, simple instructions in my native language, and extreme ease of maintenance. Still driving it 43 years later.

From your pic, looks like the anti-dieseling solenoid is not connected.

Here's a pic I took last week. Front bumper is off as I need to get it straightened out a tad. Then off to the powdercoater for the same colour as the grille.
The truck was a California import, and was built at the Oakland plant. it has the TH350 gearbox, and the engine is a Saginaw build 400cid. Carb which you can see is the Rochester R2-2GC type.
Well spotted seeing the disconnected solenoid.

[geezer#99]

Is it really a GMC or just has a hood?
You got a pic of the inside?

I'd just build a block off plate for the egr.

[andy d]

Originally Posted by geezer#99

Is it really a GMC or just has a hood?
You got a pic of the inside?

I'd just build a block off plate for the egr.

yep genuine GMC.
The front moustache type grille was missing, and I prefer the Chevy type grille anyway.
Here's a photo of the dash with the butterfly panels, rather than the Chevy V shaped one.
The panels were pretty badly pitted as you can see from the left hand photo. I powdercoated them instead and am happy with the results.
I knocked off work early and made up a block off plate this afternoon.
stuck it on, but still having the same problem. Engine dies unless you give it some gas. It just won't idle at all.
Back to the drawing board I think.

[geezer#99]

Maybe you should check your timing and the supply wire to your hei. Looks like it's spliced right behind your valve cover.

['68OrangeSunshine]

I was reading on the internet [not this site] that some ''fleet ordered'' GMC trucks were rebadged Chevy trucks w/o the mustache chrome. However you have the GMC rounded gauges rather than the ''V'' shaped Chevy speedometer and gauges.
Another small detail, GMC trucks in this MY had the base 270 L6 but could be optioned w/ a Pontiac 216 V8. So is your 400 SBC Pontiac Blue or Chevy/GM Mid-'70s blue? Hard to tell shades on a computer. "Poncho Blue" would be a cool engine color choice on your rig.
Since you're still having the same gripe, I'd go thru the full tune up, starting with a carb rebuild. HEI component check [Cap, Rotor, Module, Coil, Reluctor], new plug wires, fresh spark plugs [@.045"] should follow.

[andy d]

Originally Posted by '68OrangeSunshine

I was reading on the internet [not this site] that some ''fleet ordered'' GMC trucks were rebadged Chevy trucks w/o the mustache chrome. However you have the GMC rounded gauges rather than the ''V'' shaped Chevy speedometer and gauges.
Another small detail, GMC trucks in this MY had the base 270 L6 but could be optioned w/ a Pontiac 216 V8. So is your 400 SBC Pontiac Blue or Chevy/GM Mid-'70s blue? Hard to tell shades on a computer. "Poncho Blue" would be a cool engine color choice on your rig.
Since you're still having the same gripe, I'd go thru the full tune up, starting with a carb rebuild. HEI component check [Cap, Rotor, Module, Coil, Reluctor], new plug wires, fresh spark plugs [@.045"] should follow.

It looks like the mid 70's blue, but that is deceiving. The actual colour underneath is orange.its a little easier to see in this picture. So clearly the original colour has been repainted at some point.
The original lines where the moustache had been were clear when I picked up the truck. I used some farecla to bring the paint up a little, and they all but disappeared. Here's a few pics of the truck before I picked it up.
Got loads more if you arent already bored to death with me.

['63GENIII]

Nice looking truck there Andy! Wish I could be of more help though. Stick with it. Its bound to be something simple. It always seems to be that way in the end.

My '63 was an Oakland truck as well. Cool truck!

['68OrangeSunshine]

No Man, you're not boring us. That's a nice truck. Your rig is just different and exotic enough to unbore us.
My '67 Chevy K/10 Suburban [long dormant project] and my DD '68 C/10 Stepside were both made at the Fremont, Calif Assembly Plant. Fremont was the successor to the Oakland Assembly which closed in '62 as Fremont opened. Most likely the same team of workers. In '82 GM closed the Fremont Plant and the facility was taken over by Toyota. In 2010 the facility became the Tesla Factory.
Chevy Engine Orange was the color for all Chevy engines in 1967 MY, ending the practice of separate colors for 230s and 250s [Blue], 292s [Green], SBCs [Orange], BBCs [red-orange], etc. GMC's motors were even red, I hear.
For the '76 MY GM went to Corporate Blue. Speculation for the change is that GM got sued by B-O-P-Caddy owners who objected to an orange 'Chevy' engine in their fancier car.

Looks like I see a little Air Force blue on the back of your passenger side [US -wise] step fender. With my dyslexia, I read your license plate as ULYSSES as per Ulysses S Grant or Homer's hero.

Won't idle, Hmm? Warped carb base plate? Leaking carb gasket? Worn pivot holes around butterflies? Hard to say with this much water between us. R&R Carb, after cleaning and see what you get.
Good luck.

[68gmsee]

Originally Posted by andy d

.....Got loads more if you arent already bored to death with me.

Looks like an assortment of old vehicles in that shop. You got any pics of that 57 Chevy?

I grew up in the 50's and 60's so am fond of that vintage vehicle. Back when you could tell the year, model, manufacturer, and in some cases, whether it was a 6 or an 8 cylinder as they passed by on the road.

[nonstop]

So just to get this straight - you didn't mess with the carb or anything else, just EGR and valve covers? Have you looked at the PCV valve and vacuum hose? They are both relatively cheap and easy to replace. And just checking, you also capped off the vacuum line going to the EGR valve?