Various engine shenanigans- 454 Sub

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Rabbit

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Well, first post here. I have an 85 C20 Suburban Silverado (originally a CA car) with a 454. It has an edelbrock 1407 to replace the california computer controlled carb, which the previous owner had "upgraded" by making a spacer out of plywood, which leaked like a sieve and got 3 mpg.

I mounted the new carb, cleaned up the fuel leaks, removed 3.4 miles of unnecessary vacuum hoses, 40lbs of unnecessary emissions controls (before you say anything- I'm in an area of AZ that has no emissions testing), got the carb idleing "well enough", and have been driving it daily for a few months.

Issue is this- Heading up the 87N out of Phoenix, which is ridiculously steep and climbs to 6700ft (my artea is at 1200ft), I started getting popping/shimmying/loss of power etc., to the point I had to pull over every 5 miles or so, let it idle for 5 minutes, then continue another 5 miles. Rinse, repeat.

It seemed to clear up at lower elevation, so I wrote it off as vapor lock or other fuel starvation. However, it has started to miss/pop under load even around town when accelerating. It's not a constant thing, some days it runs great, other days it wheezes like at asthmatic getting to 35mph.

In anticipation, I bought new plugs and wires, and will be checking the timing/tuning the carb. What should I aim for timing wise? Is the stock fuel pump okay for a 750cfm carb? The california one seems to have been a 500cfm one- Are the posts I am finding about cal trucks having hotter plugs correct? I'm normally a classic beetle guy (I have a 67 baja), but this is my first proper square body, and I want to do it right. (actually the second, I had an 82 K20 longbed... that was stolen a month after purchase. But that's neither here nor there)

I know this is alot of questions, but again... Brand new to this thing. Any help would be awesome.
 

1987 GMC Jimmy

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You said it was an E4ME Quadrajet, but I've never heard of those on a big block. I would think all fifty state big block trucks would have gotten an M4M series Quadrajet. An E4ME is distinguishable from others by a three pin TPS connector sticking out at an angle from the body of the carb and an MCS top of the air horn where a dual stage accelerator pump connector would be on other Quadrajets. Another indicator of whether or not it had an E4ME is the presence of a "Service Engine Soon" light in the cluster (unless it was swapped at some point). I think it's important to firmly establish that it was not an E4ME because those have an ECM that controls the distributor, trans lockup if it was a 700R4 or TH350C, and various sensors throughout the engine bay, and nothing will work right without that E4ME.

Assuming it was a run of the mill big block Quadrajet and attempting to address some of your other questions, the new carb will be fine with the old fuel pump (unless, of course, it's not working properly). CFM has to do with air, not fuel, and big block Quadrajets can take in up to 750-800 CFM depending on what they came on. I don't know what you're talking about in respect to spark plug hotness. The only variable that I can comment on is gap spec, and I'm honestly not sure if it needs to be .035 or .045. On the timing, I'd shoot for 10* BTDC initial. If it pings, retard it a couple degrees, and try that. If it runs great, and you want to squeeze a little more out of it, advance it a couple degrees. Just don't let it ping, and it's not a big deal if you need to retard it.

Moving onto your problem, I have a few questions and concerns for you. What kind f distributor is on it? I'm not 100% sure what kind a CA big block would have, but I'm assuming it's just a regular vacuum advance distributor. Also, did you put an inline fuel filter on when you ditched the Quadrajet? Those have the fuel filter inside the carb right where the fuel goes in. Are you sure you fixed all the vacuum stuff, everything's plugged in that needs to be (especially vacuum advance), and nothing's leaking including the vacuum modulator and carb base gasket? I'd get a vacuum gauge if it were me. Very useful diagnostic tool. If you can answer these questions, review the vacuum stuff, and also work your throttle while looking down the throat of the carb to make sure your accelerator pump is delivering two healthy squirts of fuel to eliminate the question of a fuel deficiency under load, I think that would be a great starting point. It sounds like some kind of lean condition to me so I wouldn't rule out the pump, and I'd pay close attention to the vacuum stuff.
 

Craig 85

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Granted my truck is a K30, but it's an orginal California truck with a 454. The factory carb is an 800 cfm carb. There are no electrical hook ups on the carb, but there is an electric solenoid vacuum control valve attached to the thermostat housing (photo 1). That hooks up to the throttle lever actuator on the front driver's side of the carb (photo 2) by a vacuum hose. My solenoid is broken and my actuator is missing, so picture 2 is from the internet. I'll have to find these to get mine to pass smog.
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Rabbit

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Granted my truck is a K30, but it's an orginal California truck with a 454. The factory carb is an 800 cfm carb. There are no electrical hook ups on the carb, but there is an electric solenoid vacuum control valve attached to the thermostat housing (photo 1). That hooks up to the throttle lever actuator on the front driver's side of the carb (photo 2) by a vacuum hose. My solenoid is broken and my actuator is missing, so picture 2 is from the internet. I'll have to find these to get mine to pass smog.
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I'll have to dig the carb out to see if it matches- It doesn't seem to, from what I remember. I do remember it has a small computer module on the LH side if the firewall- I had to detach it since the vehicle kept throwing "check engine" lights at me, which confused me, since it's basically all mechanical now.

1987 GMC Jimmy- I'll try tuning it initially to 10deg BTDC, see how that works out. I have seen in this forum that 454s like alot of timing- I saw 20deg to 40deg listed on this very website, so I'll try yours first and let you know. Thanks for the info!
 

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I'll have to dig the carb out to see if it matches- It doesn't seem to, from what I remember. I do remember it has a small computer module on the LH side if the firewall- I had to detach it since the vehicle kept throwing "check engine" lights at me, which confused me, since it's basically all mechanical now.

1987 GMC Jimmy- I'll try tuning it initially to 10deg BTDC, see how that works out. I have seen in this forum that 454s like alot of timing- I saw 20deg to 40deg listed on this very website, so I'll try yours first and let you know. Thanks for the info!
Yes and no on the big block timing yes they do with the right fuel to much timing and **** gas will yield you a big baby rattle. And a turd to boot. I run 36 degrees locked with 50/50 C16
 

1987 GMC Jimmy

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I gotcha. I deal almost exclusively in small blocks. I've only ever really worked extensively on one 454. What you pulled from the firewall sounds more like an ESC module. An ECM is somewhat bigger.
 

Rabbit

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Yes and no on the big block timing yes they do with the right fuel to much timing and **** gas will yield you a big baby rattle. And a turd to boot. I run 36 degrees locked with 50/50 C16

Alright- New plugs! Old ones had some detonation damage (probably from the dieseling) but were an even gray. New wires! Old ones came apart as I detached them- Seems they may have been the originals from 85. Means the plugs were too. Timing was set at 8*, so I advanced it to 10*, and the truck is purring like a kitten. Got my power back, no hesitation on throttle, no sputtering on load. I'll try this for a few days, see how it works out. I probably need to tune the edelbrock 1407 a bit, but it idles nicely (about 800rpm) starts well and doesn't bog when put into gear. Thanks for the help, I'll keep you updated!

Edit- I was running 91 octane in an attempt to stop the dieseling. Should I keep up the premium, or try out regular?
 

Rabbit

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Oh, and if I never have to get that #8 plug out again, it'll be too soon.
 

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I would say from what you mentioned before that your timing setting is somewhat conservative so I'd just go back to 87 if it were me. Even if it were my 350, I'd still switch it back.
 

Honky Kong jr

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Alright- New plugs! Old ones had some detonation damage (probably from the dieseling) but were an even gray. New wires! Old ones came apart as I detached them- Seems they may have been the originals from 85. Means the plugs were too. Timing was set at 8*, so I advanced it to 10*, and the truck is purring like a kitten. Got my power back, no hesitation on throttle, no sputtering on load. I'll try this for a few days, see how it works out. I probably need to tune the edelbrock 1407 a bit, but it idles nicely (about 800rpm) starts well and doesn't bog when put into gear. Thanks for the help, I'll keep you updated!

Edit- I was running 91 octane in an attempt to stop the dieseling. Should I keep up the premium, or try out regular?
Octane and timing go hand and hand. So if you bump up to 12 I'd keep the 91
 

74 Shortbed

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All depends on the total advance..
 

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All depends on the total advance..
I've always locked mine and if it liked more then it was easy to start the distributor was on a switch and relay.....starts cranking and throw the switch.
 

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I would say from what you mentioned before that your timing setting is somewhat conservative so I'd just go back to 87 if it were me. Even if it were my 350, I'd still switch it back.
Higher octane better burn more efficient combustion better mileage.
 

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I've always locked mine and if it liked more then it was easy to start the distributor was on a switch and relay.....starts cranking and throw the switch.
Yeah that works, I always lock them out on blown motors but anything else I'll set it up for total to be all in by 1500rpm, that way don't need to crank first but yet may as well be locked out..
 

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Yeah that works, I always lock them out on blown motors but anything else I'll set it up for total to be all in by 1500rpm, that way don't need to crank first but yet may as well be locked out..
I learned the switch trick long ago and well it's stuck with me lol
 

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