My problem is my 1984 366 is really down on power. The truck is a1984 GMC C-7000 with 98648 miles on it. It has 366 cid or 6.0 Letter gas engine with a new Edelbrock 1905 on it. It has new plugs, wires, distributor cap and rotor. It runs but it is a real dog. I can not get the truck over 15-25 mph. I have another 1993 Topkick that does a lot better (also a 366). What could be holding the engine down? I know there is more torque in there, but how do I get it out?
Just throwing stuff out there: “Can’t get over 25mph” Is that empty? “New plugs, rotor, etc” Did you get the cap and wires in proper firing order? I’ve messed up and had a couple cylinders off (or even 180degrees off) and it’ll run but no power. Darryl
Off the top of my head...... Intake restriction, exhaust restriction, timing is off, fuel supply is restricted, fuel pump weak, fuel filter plugged, brakes dragging, vacuum leak, low compression or maybe valve burnt or sticking.
First - Thank you. Your ideas are much appreciated. I checked the spark plug wires - all good, rotor is new and obviously working, the coil is new (but that does not mean it is working correctly). But in going through this, I think I have a lot of vacuum leaks and maybe an exhaust leak. The air filter is massive and new, the timing was coarsely set, but I think it was not tuned, fuel pump is new and the tank refurbished (no junk, sealed, perfect) the fuel filter is clean and clear. Brakes dragging - hummm, maybe. Vacuum leak - absolutely, Low compression - I will redo a compression check. So from you two (Junkyard and Labparamour) Thank you. I think I am going to start running down the vacuum leaks and seal up the exhaust, pull the plugs and redo the compression test (I remember 130, but it is a vague memory - I will write it down. I don't like the idea that is is worn out (need rings and valve job?, if so - bad news) It may be correct, but I hope not. It is not worth rebuilding
BTW, it is a crane and it is close to 24000 lbs.
You need to hook up a vacuum gauge to the intake manifold first. That engine should run 18 inches of vacuum at idle. What carb came off that engine? spread bore? The 1905 is a square bore and if not using the right base gaskets or adapter can cause vacuum issues. Is the mechanical advance/vacuum advance working? The mechanical advance was know to freeze up in those distributors. If that year still uses one. Does this truck have a vacuum booster for brakes?
Also, since this appears to be a replacement carb, is the linkage opening the throttle butterflies fully?
When you check the compression block the throttle WFO.
You're certain that 5 & 7 aren't reversed? Been there.
So the firing order in 1-8-4-3-6-5-7-2 and 5 and 7 should be looked at? I have the compression tester out and will run them all, then rewire it
I am not sure i understand this. How would I do that? Thanks
I will recheck this. There are certain physical limitations with the current setup. The rod off the pivot on the firewall is a certain length. If I need to lengthen this, I need a workaround.
He was saying check compression with the throttle wide open.
It’s very common for 5&7 wires to get inadvertently swapped. Just make sure they’re all in the correct spot.
Hi the compression test show 1- 175psi 3- 170psi 5- 155psi 7- 155psi 2- 155psi 4- 145psi 6- 140psi 8- 145psi
Also, I checked the wiring - it is correct.
No paper gasket under an AFB ever, only the thicker insulator ones, if I remember correctly. Didn't those have a little spud up behind the dash you had to unplug to establish base timing. Also, I remember that those manifolds would glow when they ran like that. Check the trigger and pick up in the distributor. I remembered that they were prone to failure, cracking, shifting etc
Your a little shy on #4,6 and 8 you want 20 psi difference only between cylinders but it should run ok where it is. Now check the vacuum
The more I think about it, the more all my headaches regarding those Tonawanda engines it all boils down to the distributor reluctor. The shaft would rust beneath the reluctor causing it to crack. Then it would slip out of phase with the rotor. Now you have a primary field collapsing onto a secondary and no place to go. Now that high energy spark jumps to any available post it can find. Good luck
We had 60 school buses with the 366 engine, that finally were taken off the road this past summer. All were from the mid 90's and all had over 235,000 miles on them. As I recall, most of the time, the mechanics would find distributor problems when the buses started running poorly. There was a whole shelf in the parts room dedicated to distributors for these old 366 engines. If a drive called in with a dead or dying bus, the mechanics loaded a distributor into the truck and headed out. MOST of the time, the new distributor fixed the problem and it was very rare to have a "tow in". You mentioned exhaust leaks. Well, a lot of ours sounded like dirt track race cars, due to exhaust manifold gasket leaks. This never seemed to hurt the engine performance much.
My 95 with fuel injection needed a new distributor. I got a Chinese distributor for under $150 and has a lifetime warranty. Came with Ignition control module and cap and rotor. Just an ignition module was the same price. Pick ups in the distributor are apparently a common problem. Every 6.0L/366 I've owned had a cracked exhaust manifold on the passenger side. 1975 6500, 1995 Topkick and 2000 Silverado 2500 pick up. I've heard it is very common but don't know why.
The ignition, the governor and they're just plain overworked.
The distributor is the same as used in pick ups which I think is why they are so cheap. I just use the truck for a water truck. If I made my living with it might go to a better brand.
There is a whole website dedicated to that pig. Including how this, that and everything else works, how to convert to this or that.
well it has been some time, but it bent a push rod. I pulled the heads and had them rebuilt. There were 2 stuck exhaust valved that had to be hammered out. It had good compression, spark, air and fuel (tests OK) but was running as a 6 and not an 8. The head rebuilder says it is common with bad (old) gas. It has probably been running with these 2 bad valves for over 10 years