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Old 10-03-2012, 11:09 AM
BogiesAnnex1 BogiesAnnex1 is offline
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Originally Posted by sherri32 View Post
My son has a 1991 Chevrolet silver-ado with a 350 vortech engine ( i am a mother and don't know anything about vehicles LOL) I bought his truck from a man who let it sit up about 5 years, when we first got the truck we put a new alternator, battery, spark plugs and wires and a new fuel pump on it. The truck ran fine for about 2 months and then one day on his way home from work. He turned off the interstate and it died. He finally made it home and I took it to a mechanic who said his number 1 and number 8 cylinders are not firing and he needs a new engine. The truck does not smoke and runs fine until it gets hot then it acts like it wants to shake when you put it in gear. My ? is does anyone know anything about this or if this has happened to them or is the mechanic right and he need a new engine? What should I do? My son is only 17 and knows nothing about cars either so i'm stumped as do i put money in this or just give up and try and buy something else.
If this engine is original to the truck it is an LO5, these are 350 cubic inches that use Swirl Port heads with Throttle Body Injection (TBI).

If the Check Engine Light (CEL) is illuminated there will be code information that can be down loaded from a connector on the bottom of the instrument panel. Go to this web site for instructions to use the connector and the CEL light to read the codes without a code reader tool: >>> How to read older GM OBD diagnostic codes for free >>>.

Go to this web site to get the list of GM OBD 1 codes: >>> OBD-1 Diagnostic Trouble Codes >>>. OBD 1 stands for On Board Diagnostics (generation) 1. This is used from about 1984 through 1995 for models with electronic fuel injection of which TBI is one of several types.

New fuel pump if this still has TBI the pump is in the fuel tank and is a pretty large effort to replace, is that what you did or had done? A fuel pump on the side of the engine, forward on the passenger side, would indicate the engine has either been replaced and the fuel system modified to a carburetor, or the existing engine was similarly modified to accept a carburetor.

Cylinders 1 and 8 are at opposite ends of the engine, 1 being the front driverís side and 8 the rear passenger side. However they follow each other in firing order (1,8,4,3,6,5,7,2), this is how the distributor cap should be wired. The rotor within the cap rotates clockwise when viewed from above, which of course is the only view of it you're going to get.

One of the risks with the Chevy Small Block is wear and loss of cam lobes where flat tappet cams are used which is what is found in the vast majority of pre-1996 pick-ups. There is always the possibility that you mechanic has diagnosed this and this could be the reason he recommends engine replacement. This is easy to check for by removing the rocker covers to watch the amount of valve action, little compared to the others would indicate a wiped out cam lobe and tappet.

A truck this old could be having problems with the timing chain and gears. This allows the cam to fall out of synchronization with the crankshaft. But this is a problem well leave for another day.

The 1 and 8 spark plug firing problem if real could be in the distributor cap. First check to see that the plug wires are pushed tightly into the cap. Then inspect their lengths for damage. Running the engine in the dark and looking for electrical arcs is one way of isolating high voltage leaks as you can see them. Given that 1 and 8 are next to each other on the cap terminals there could be arcing between them inside the cap. Removal of the cap and careful inspection will show trails that look a lot like a crack in the plastic. Part of the tune up for the HEI ignition should include a cap and rotor as the high energy of these systems erodes the contacts.

Check engine vacuum, this is a pretty mildly cammed engine so it should be high certainly above 16 inches at idle and steady. A vacuum check is a good diagnostic to isolate problems. Follow this link for more detail: >>> How to Use and Interpret a Vacuum Gauge >>>.

I'd highly recommend purchasing a service manual for this truck. The common over the counter manuals from Haynes or Chiltonís are reasonably priced and contain a wealth of information.

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