high speed engine miss

[markdpro]

I have a 350 yukon 1997 with 54 000 miles
I tow a 3500 lb boat
After a long uphill pull at 50 mph, there is a heavy engine miss when I come off the throttle and then open the throttle to continue at speed. There is no miss as long as I don't back off and then come back on.

New platinum plugs New spark leads new fuel filter new pcv valve no change.

This weekend a flashing check engine light added to the fun but under moderate load, no light and it went off as I continued under moderate load.

There is a little induction rattle at light load.

I'm wondering if the dealer (ach) didn't seal the manifold properly when they replaced the intake manifold injector body gasket and somehow a vacuum leak is causing preignition in the manifold??

I hate to go to the dealer with an intermittant fault

any ideas?

markdpro

[markdpro]

Originally Posted by markdpro

I have a 350 yukon 1997 with 54 000 miles
I tow a 3500 lb boat
After a long uphill pull at 50 mph, there is a heavy engine miss when I come off the throttle and then open the throttle to continue at speed. There is no miss as long as I don't back off and then come back on.

New platinum plugs New spark leads new fuel filter new pcv valve no change.

This weekend a flashing check engine light added to the fun but under moderate load, no light and it went off as I continued under moderate load.

There is a little induction rattle at light load.

I'm wondering if the dealer (ach) didn't seal the manifold properly when they replaced the intake manifold injector body gasket and somehow a vacuum leak is causing preignition in the manifold??

I hate to go to the dealer with an intermittant fault

any ideas?

markdpro

I have pondered this at great length and the best I can come up with is induction icing. With a few crystals of carbon in the induction system, enough ice might accumulate at high throttle settings to cause the stumble when the throttle is closed. Spraying the system with cleaner may have removed enough of the seeding areas to cure the problem????????????????

[radioman2002]

Try something even simpler, check the coil, mine was bad and drove me nuts. After, trying to reset the timing 5 times, (engine had just been rebuilt) Had to go back to basics and check all the simple stuff, when I pulled the coil wire away from the screwdriver I had stuck in the coil to test it, the went dead, after replacing the coil, I now get about 3/4 to 1in of spark, before it dies.