Gmc 454

[mro]

Let's see.... 50,000 miles at 4 to 5 miles a gallon.... lol.

Mines got 240,000+
Once upon a time it got 14mpg on the high way with light loads and just about 12 pulling a trailer. Now lucky to get 10 with a tail wind.


mro

[HobbyMan]

WEll, towing a 10,000 lb travel trailer it gets 7-8 mpg. With big bias ply tires, and the standard rear end, It does well. The dealer wanted my dad to get the lower ratio rear end, that would kill milage. With a 454, you don't really nead the lower differential. I am looking into some good headers that was on my friends chevelle SS454, but that is my last option. This is now getting put on the back burner because of some sensor problems screwing up fuel delivery. Maby the CDI is bad or something. I have a chiltons for it, but it does not cover everything. The other day, one of my dad's 79F's lost ignition on the inner spark plugs. It is probalby a pickup coil, but I have soo many things to do this weekend, and finals are next week, I won't have time for a while to work on the truck. I am putting all of these ideas together and trying to form some conclusions on the best way to handle this truck. I was going to get the engine running properly and polish the whole truck as my Dad's Christmass presant, but just getting him an XS11 hat is much easier. I haven't even been able to find out if the stock manifolds are available. I was also wondering about the manifold bolt pattern. Are there any differences between a early 70's 454 and a ealry 90's? It is basically the same as the 88-89, but with the new TBI.

[RUSH]

I wouldnt get SS bolts if I recall correctly they dont have the strength of even standard bolts. if you are going to change them go for the hi tensile bolts.

[mro]

exhaust

The stock cast iron manifolds are prone to cracks. If yours are still good the gasket should take care of leek. Have talked to some RV guys (454 was popular) and cracks in stock exhaust manifolds was said to be common.

If I decide to keep mine, may buy a new long block from the local GMC truck center along with steel exhaust manifolds. Other option is getting a diesel. Fuel cost more but better milage.

fuel delivery

If you have the "throttle body fuel injection" may want to pull injector out and make sure it's clean. Some can be disassembled and there should be a fuel screen. Also check fuel pressure. Just because you can hear the fuel pump don't mean it's working properly. The computer can go bad but not as common as other problems.

mro
btw
Merry Christmas

[HobbyMan]

I took both injectors out and cleaned them the other day. It is still struggling a bit. The TCI went bad already once before. The unit that is in there now is a rebuild one that was done by a company in FT. Worth, I think. It could just be a sensor.

[Sluggo]

Naturally, you used the A.L.D.L to pull the codes from the computer. This would be the wisest way to proceed. There are a ton of sensors that could cause the vehicle to run poorly. If your Chilton manual doesn't give you the needed information and flowcharts to figure out the problem, may i suggest making a stop at your local library and see if they have better manuals. You may not be able to take the book home but you can copy the pages that show you the procedures.
By the A.L.D.L., i mean the terminal under the dash board that you stick the 2 pronged tool [ or piece of wire] into and count the "check engine light" flashes. this gives you a code of what the computer sees as being out of whack.
Good luck

[HobbyMan]

I have the code reader. i thought It only worked when the engine light was on?

[goldcoastguy001]

I raced a 77LT camaro for 7years with a 454cu, had headers on it but I can say for sure that S/S bolts are a waste of time....they heat up to fast and cool too quickly for the head you will end up having to tighten bolts every other week.....change the gasket with a good alu/fibre gasket and H/T bolts and tighten the hell out of them you wont have any problems after that I can gaurantee it. also make sure timing is correct flames out the exhaust is a sign of to much advance on the timing....big blocks generally wont ping with too much advance unless it is really advanced just a side note they run exceptionally with vacuum disconnected and timing static set at 38-40degrees....the springs in the dizzy advance mech lose tension and advance it prematurely........

[dpotter58]

"Yeah, I have heard from a number of peple now that have had cracked heads"

You'll find a few on here like that but most of us are OK...

[planedick]

Gaskets?

After replacing an engine in a chev van and the shop put gaskets on the exhaust manifold. Whoa, the dealers all tell me that is the reason the manifold cracks or warps. Chev (GMC) engines haven't had exhaust manifold gaskets since they came out with the 283. WWAaaaayy back when. Check with your local GMC dealer.

[goldcoastguy001]

its not really gasket of sort more like like a thin shim type gasket for lack of a better word.....normally like tin type stuff...you can get a alu "gasket" for it...(bit like the inlet manifolds use to have..)

[planedick]

No gasket....

No gasket is better as the engine soaks up the heat so the headers don't overheat and distort or crack....

[HobbyMan]

FINALLY got around to getting this truck running last weekend. New plugs and starboard manifold. We were going to opt for a good set of headers but none will fit. Manifold was our only choice. The TBI is now freshly rebuilt and all that is left is to check some of the wiring. We put the original MC which we rebuilt a year or two ago. The cheap replacement finally gave out. My Dad is using this truck to get our excursion back from Colorado. We'll see what kind of mileage it gets with this new ethanol gas. Probably really low. Other than a little exterior polishing, this truck would make a good magazine cover. I am glad to say that it gets more complements than any of our XSs. They also come from a much wider range of people. What can you expect from a pre '88 body style 91'GMC dually pickup? IMHO, the last vehicles that came close to it were the 7.3DL '02 F350s.

[Crazcnuk]

"Let's see.... 50,000 miles at 4 to 5 miles a gallon.... lol. "


My 502 (Gen VI Chev big block) gets 14mpg, with 3.70 gears and no overdrive....

[HobbyMan]

I think we got around 7 mpg towing 4-5 tons worth of trailer and excursion.