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1998 454 chevy engine in a tiffin Motorhome Garry Walker 4-25-15  
I have a 7.4 fuel injected engine in my Motorhome. It has started missing on 4 of the 8 cylinders. I have removed the injectors and had them cleaned and new baskets fitted by an injector shop. I have replaced the spark plugs woth new iridium ones recommended for this engine. I have checked the leads and they are all working fine. All of this has made absolutely no difference. Any help would be greatly apreaciated thank you
Garry Walker
Re: 1998 454 chevy engine in a tiffin Motorhome BUBBA THE BUS TECH 4-28-15  
Common problems causing this:

But first compression test.

In order of cost to fix:
Firing order, Very common, Bought two Pickups with this problem. Towed away, ten minute repair + oil change. Sold for a silly profit in less than a week
Blown fuse for 1/2 of injectors. Most GM product of this era have a fuse for each 1/2 of the injectors. Tech way to check is called a Noid LIght plugged in in place of an injector. Personally I pull the plugs for a Compresion test and find there is no wet or raw fuel on the 4 of the plugs, if the sytem is injecting and not running there should be, I look too this first before running the compression test.
Blocked or plugged exshaust
Intake gaskets or other large vacume leak. Usually kills one side of the engine. I use a propane torch to check this.
Cam shaft, remove valve covers and check by measuring valve lift.
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