1994 MotorHome 454 Chevy Engine

[Micasa]

I have a remanufactured 454 7.4 liter Chevy engine in my MH. It was installed in late January of this year in Lodi California. I drove it about 200 miles and it started backfiring, has very little power when needed to climb, accelerate, etc., and my mileage is has gone down about 2 mpg. By the time I got to Phoenix it was runnng terrible. The Lodi shop authorized us to go to a local RV shop to have it analyzed. The AZ shop found two spark plug wires burnt in half and one spark plug ruined (These were all replaced with new during the install) They were replaced and all ran well for a while. Stayed in one place for about 3 weeks and then went to Mexico and after about 300 miles it started backfiring again. Parked for 3 weeks and came back to Arizonia and again it was almost undrivable. I found the timing set at 0 degrees instead of 4 degrees per the engine specification so I changed the timing and drove it about 150 miles and it started backfiring again. Talked to Lodi shop and they said it was the AZ shop's problem as Lodi had paid them to fix it. AZ says they just did what Lodi authorized. So I replaced all spark plug wires with high heat wires, (the ones I took out were either burnt through or had the start of holes burnt in them). I checked the plugs and found that 7 were apparently new with no carbon and one was one of my old Plantinum plugs from the previous motor. I put two new ones in (of course Lodi didn't put the platinium plug in, per them it must have been someone else but since they kept those when they put the new ones in I guess it was some kind of trick that got the old platinium plug from the old motor into the new one). The rotor had carbon on it so I replaced the rotor and distributor cap and it ran good for a while. Now I am in Las Vegas and it is again backfiring, goes up a hill at about 25 mph, and the smell of gas is strong. I am parked for awhile and haven't look at anything but expect to find the same problem as the last two times. Does anyone have any suggestion as to what is causing this problem or how I might solve the problem?

[84fiero123]

are the wires burnt thru because they are in contact with the engine if so put wire hangers in place they usually hold the wires in a safe place, they should have been put on in the begining, if thats not the problem then it sounds like the wires are defective. try factory wires for that engine or wires rated for raceing. try a gm dealer not mh dealer, it is a gm engine. never liked those platinum plugs, try ac delco, i find they work better on gm engines, don't know why but they do

[Micasa]

No the wires are not burnt because of contact, they are in a harness as required The platinum plugs were in the old motor, not the new and worked fine in it. The Lodi shop did put AC Delco plugs in the unit in 7 plugs and I replaced the platinum with a new AC Delco. Most GM dealers are not set up to handle motor homes and won't work on them. The Lodi and AZ shops were both autorized GM shops. I just don't know what could be causing this extreme heat in the plug that are burning the wires. It appears that the fuel is not burning properly. Got any suggestions?

[Autopro]

It is very difficult to troubleshoot without seeing the vehicle. But if the wires are ok and you smell gas I would check the throttle body or carb. It sounds like the engine is flooding. When an engine floods the spark plugs get wet and the engine will misfire and backfire. Bad timing would also cause this and a list of other things.


AutoPro

[84fiero123]

autopro is right flooding is a major problem in itself, but is this engine carb. or in jected you didnt say? if it is carb. you may be out of ajustment running to rich. that could be why you smell gas and the roten millage. but like he said its hard to diagnose without be there. try stoping at a napa for new wires and get a set of wires i find these guys usually know more than most other parts stores, because they work at shops of there own . good luck

[mike_24_oh]

well if it is a newer motor and if it has a controll module that could be your problem because the controll module has to do with your firing and your fuel trust me been down that road before on my car if its going bad it will lack of power but a 454 may not have one but i would like to know what you did with your old 454 im looking for one dont matter if it runs or not please let me know

[IFIXCARZ4U]

On big block chevy motor s there should be a sheetmetal heat shield that bolts to the exhaust manifold. If these were left off during the rebuild excess heat will destroy new wires in no time due to the lack of cool air around the engine in a motor home. It is just a tubular type metal shield that goes around the spark plug boot. hope this helps

[Micasa]

Originally Posted by mike_24_oh

well if it is a newer motor and if it has a controll module that could be your problem because the controll module has to do with your firing and your fuel trust me been down that road before on my car if its going bad it will lack of power but a 454 may not have one but i would like to know what you did with your old 454 im looking for one dont matter if it runs or not please let me know

The old 454 was exchanged for the rebuilt engine. Sorry!

[Micasa]

Originally Posted by IFIXCARZ4U

On big block chevy motor s there should be a sheetmetal heat shield that bolts to the exhaust manifold. If these were left off during the rebuild excess heat will destroy new wires in no time due to the lack of cool air around the engine in a motor home. It is just a tubular type metal shield that goes around the spark plug boot. hope this helps

Right on, I talked to a local GMC MH and Race car mech here in Vegas and he said he would bet they didn't put the liners in the sheetmetal heat shield when they installed it on the new motor (he was right, and you can bet the Lodi shop will never see my unit in their shop again). When this motor was originally installed these liners were a cardboard type heat shield but GMC recommends an asbestos type now. So $385 later (new wires for the 3rd time, 2 new plugs, new dist. cap, new rotor, and new shields, and about 10 hours of my time) I think I have the problem solved. We will test drive tomorrow and make sure because it takes between 100 to 200 miles before the wires burn enough to start backfiring. Since it is a fuel injection unit I had eliminated that it was running too rich, besides the wires just keep burning (replaced them 3 times now). The mech said it couldn't be the module, because if it was bad this engine wouldn't run long enough to get the wires hot enough to burn off, it couldn't be the coil for the same reason, nor could it be the catalytic converter blocking air and making it run hot, if it needed to be replaced the engine would slow down and finally stop. So hopefully he is right (his advise was free) and this will be the end of this.

[mike_24_oh]

how much did they give you for the old engine when you got your new one

[Micasa]

Originally Posted by mike_24_oh

how much did they give you for the old engine when you got your new one

All the details in price were completed by the shop with our insurance company, so don't have an answer for you. Sorry took so long to reply but made a trip to Mexico and just got back.