Flashing engine light / no power under WOT or heavy load

[04SS99Denali]

Im lost. The truck runs great under normal throttle, Idles smooth not misfiring or anything. Even at around 70% throttle up till 4000 it runs great. When I put it under heavy load (going up a steep hill) or WOT condition it will lose all power and start to shudder as if its misfiring. I pulled the cap rotor, cleaned them again they were replaced 3 years ago (only 5k miles ago). New plugs, new wires also done 5k miles ago. Right now there are no pending codes. Also has a new fuel pump, did this before and still does it after.

Little history, replaced the intake gaskets 3 years ago so pulled the distributor. I lined it up back then and checked again today, put cylinder 1 to TDC and the arrow on the cap is pointing toward the #1. So I do not think its a timing problem.

It did not do this before everything was replaced. Which is why Im confused because nothing seems to be put back wrong.

Any suggestions would be very helpful lol

 

[OR VietVet]

I would be wondering about catalytic converter back pressure. If you have an infra red temp gun, start the engine and let get warm and then give us front of and rear of temp readings at the cat(s). Check fuel pressure as well. Can get bad newer parts. Best if you attach a gauge for the fuel pressure and get a reading at idle and then tape the gauge to the windshield and drive it under the mentioned load conditions and tell us what those readings are. You can sometimes rent a fuel pressure gauge set or buy a cheap one at Harbor Freight but make sure you get a long enough hose to snake out and tape to windshield.

 

[04SS99Denali]

I really don't think its fuel pressure because it was doing the same symptoms before and after the new pump. But definitely worth a shot. The old one completely died out on me luckily it died in the garage after a long winter of sitting lol. You know I never thought of the bad cat idea Im going to do run it and check temps. I will get back to you.

 

[Doubeleive]

flashing check engine light is a misfire, I would take a fresh look at the cap/rotor, if there is a small crack or something it could be the problem, did you use OEM parts or something cheaper?

 

[04SS99Denali]

I just pulled them both off this morning, gave it a quick cleaning / filing. Looks good. Last time I experience the power loss the CEL did not come on. Truck just lost power and shuttered. I should also add it takes a few seconds for it to regain itself after an episode. Even after I let out of the throttle

The rotor is Delco and I believe the cap is auto parts store brand

 

[GreyStone]

Have you changed the fuel filter.. Would also help if you say what vehicle we are talking about.

 

[04SS99Denali]

Ive been out replicating the issue running live data logs on my scanner and it has yet to throw a CEL.It will still lose power under WOT / heavy load.

No I do not think its been changed at least in the last 50k.

 

[PG01]

Did you make sure everything was plugged in tightly at the little connectors at the distrib, none the pins on the connectors bent over, no wires broke etc. sounds timing related to me.

 

[04SS99Denali]

Did you make sure everything was plugged in tightly at the little connectors at the distrib, none the pins on the connectors bent over, no wires broke etc. sounds timing related to me.

Exactly what I thought. Which is why I pulled the cap / rotor to make sure the timing was right. Everything seems fine. Plug wires are new. All the connections are in. The truck doesn't even go out in the rain it just sits in the garage lol.

I was going through all the systems for pending codes and there is a MAF code pending. I cleaned it and erased the code. I am going to go replicate the problem again and see how it does.

The more I replicate the issue the more it appears to be a load bearing problem. It will rev out to like 5 and change in 1st gear, once it starts to build load in 2nd is when the power loss starts to happen.

 

[PG01]

Maybe your intake gaskets have a leak and its pulling timing at higher rpm ???? Thinking off top of my head