1996 Chevy 454 runs rough #5 and 6 not firing

Started by changing the plugs in all 8 then wires,cap and roter,Checked and compared all compression all 8 close to the same. I know it is 5 and 6 because there is no change when the plug wires are on or off the cap. No check engine light I havent pulled any codes yet, they charge $75. to do that but I may have to.

Could it be in the fuel system? I would have to take of the plenum to check, lots of work and it is in a motor home so there isnt alot of room to work.

Could it be the cam? It is strange that it is 5 and 6 they are across from each other. Oil seems to be ok and not full of fuel Exhaust seems rich and it is eating gas

Any idas or suggestions would be helpfull. Thanks Boxer

Reply to
dbox
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Boxer wrote: ( 1996 Chevy 454 )

Cylinders #5 and 6 do not fire. I changed plugs, wires, cap and rotor. Compression for all 8 is good. There is no change with the 5 and 6 plug wires are on or off the cap. No CEL.

Could it be in the fuel system? I would have to remove the plenum to check, it's in a motor home not much room to work.

Could it be the cam? It is strange that it is 5 and 6 across from each other. Oil seems to be ok and not full of fuel. Exhaust seems rich and it is eating gas. Any ideas? ___________________________________________

High gas consumption can be expected if 2 cyls are not firing.

Some firing orders such as 1_8_4_3_6_5_7_2 make it easy to mistakenly interchange the #5 and #6 wires at the distributor cap. Confirm actual firing order and recheck wire installation.

Distributor cap shorted or cracked between the #5 and #6 posts.

Cap on crooked - rotor is too far from #5 and #6.

Vacuum leak in manifold near #5 and #6 intake ports.

Two bad individual injectors at #5 and #6.

Two bad plugs. Remove the #5 and #6 plugs, lay them on a metal engine part, attach the plug wires and crank the engine. If there is spark, plugs and wires are probably okay.

Probably not the cam because compression is okay.

Good luck.

Rodan.

Reply to
Rodan

5 and 6 were not fireing befor i changed out cap,roter,plugs and wires, the cap is the new type and has the even on one side and odd on the other with the corrisponding # on it so i am shure they are correct.

It is the type of manifold that has 2 rails in it feeding the cyclendres id doesnt have individual injectors. It could be a bad rail or tube?

Whare would i check for a manifold air leak between 5 and 6 or shouldi spray wd40 near there and listen for a change in rpm?

Reply to
dbox

"Not firing" Just what does this mean?

No spark at the plug? Plugs sparking fine, but an error code is being stored?

Reply to
Noozer

cracked rings or you need valve's checked and may just be a couple pushrod off.....

Reply to
Scrapper

oh you must be working on model cars all those years.....so you must be on crack......

Reply to
Scrapper

Boxer wrote: ( 1996 Chevy 454 )

Cylinders #5 and 6 do not fire. I changed plugs, wires, cap and rotor. Compression for all 8 is good. There is no change with the 5 and 6 plug wires are on or off the cap. No CEL. Could it be in the fuel system? I would have to remove the plenum to check, it's in a motor home not much room to work. Could it be the cam? It is strange that it is 5 and 6 across from each other. Oil seems to be ok and not full of fuel. Exhaust seems rich and it is eating gas. Any ideas? ___________________________________________

Some firing orders such as 1_8_4_3_6_5_7_2 make it easy to mistakenly interchange the #5 and #6 wires at the distributor cap. Confirm actual firing order and recheck wire installation.

___ Dtributor cap shorted or cracked between the #5 and #6 posts. ___ Cap on crooked - rotor is too far from #5 and #6. ___ Vacuum leak in manifold near #5 and #6 intake ports. ___ Two bad individual injectors at #5 and #6. ___ Two bad plugs. Remove the #5 and #6 plugs, lay them on a metal engine part, attach the plug wires and crank the engine. If there is spark, plugs and wires are probably okay. ___ Probably not the cam because compression is okay.

Good luck. Rodan. ____________________________________________________

=== 5 and 6 were not firing before new ignition parts were installed. === Distributor cap is the new type and has the evens on one side === and odds on the other with the corresponding # on it so I am === sure they are correct.

You don't know that they are "not firing", because you have not taken those two plugs out and visibly observed the sparks. This is the first (and zero-cost) test needed. Then you can decide what further action to take.

=== The manifold has 2 rails feeding the cylinders. It doesn't === have individual injectors. It could be a bad rail or tube?

If there are injectors, a couple could be dribbling fuel. Fuel rails feed smaller tubes that usually go to injectors. Sorry, I have no experience with tubes that don't end in fuel injectors.

=== Where would I check for a manifold air leak between 5 and 6 === or should spray WD-40 there and listen for a change in rpm?

It is a small probability of the cause. I meant a big vacuum leak, like a brake vacuum port in the manifold left open.

Notes

Another possible cause: a sloppy bearing in the distributor that lets the shaft lean off-center, so the rotor passes too far from the #5 and #6 terminals.

A flat cam lobe, a burned valve, a bent pushrod, or broken piston rings could cause misfiring, but you confirmed that compression is acceptable and uniform, so the problem must be elsewhere.

Good luck. Rodan.

Reply to
Rodan

If its a 454, its either got bent pushrods or well bend some pushrods if it doesn't throw a rod through the block or get totalled in a wreck first. Some things never change. Pop the valve cover and replace the bent pushrods.

Reply to
Steve

i will give it a look it soinds like the easiest thing to check next. although 5 and 6 have the same compression as the rest.

Reply to
dbox

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