Motor Heads! 1995 454 chev engine misses

I’m pulling my last bit of hair out.

The engine will miss randomly and with the higher rpms, the miss is very pronounced.
That meaning the tach will drop like the key was turned off down 1000 rpms.
@ 1000 rpms the tach drop just a little.
@3500 rpms the tach will drop 1000 rpms.

*Some of the items below were done because it was time for a tune up.

Replaced complete distributor
Replaced plugs and wires.
Replace two fuel filters and fuel/water separator.
Switched injectors with other engine.
Replace fuel pump.

On the good engine the fuel pressure is rock solid.
On the engine I’m having trouble with it is constantly wiggling and we can see the drop in pressure when the engine misses.

Can’t be bad gas as we just ran both engines for 60 hours with the same gas in each tank.

Where to look next?

Fuel lines to that motor?

HRG

Mechanical fuel pumps or electric? I would put a volt meter on the ign box to verify that you have a full 12v all the time. Sounds like a random loss of power to to the ign system. Check all the spark plugs on that engine.

Sounds like a weak pump, swap pumps and see if the issue follows it. Missed that you replaced it so not likely, but keep swapping parts, the ECM?

onestout wrote:

On the good engine the fuel pressure is rock solid.
On the engine I’m having trouble with it is constantly wiggling and we can see the drop in pressure when the engine misses.

Would the ECM do that? I don’t have a clue.

Since everything has been replaced from the first filter to the injectors and I’m still having issues with the fuel pressure (if it’s not the ECM) all that’s left is the fuel line and pick up….right?

Brian Klawitter wrote:

<div class=”d4p-bbt-quote-title”>onestout wrote:</div>
On the good engine the fuel pressure is rock solid.
On the engine I’m having trouble with it is constantly wiggling and we can see the drop in pressure when the engine misses.

Would the ECM do that? I don’t have a clue.

Since everything has been replaced from the first filter to the injectors and I’m still having issues with the fuel pressure (if it’s not the ECM) all that’s left is the fuel line and pick up….right?

I am assuming fuel injected, a disruption in power to the pump could be the issue. Make sure all grounds are clean and tight. Swap computers, etc. until the mis moves.

In 1995 a 454 had a PCM and unfortunately the eprom for it is discontinued. There is no TSB’s either which sucks.

onestout wrote:

I am assuming fuel injected, a disruption in power to the pump could be the issue. Make sure all grounds are clean and tight. Swap computers, etc. until the mis moves.

The ECM is the only thing we haven’t changed. Guess that’s next.
There a solid 12.5 + to the pump.

No clue what Jeremy said. LOL!

Check your fuel tank vent for clogs.

Lots of spiders around!

Brian Klawitter wrote:

<div class=”d4p-bbt-quote-title”>onestout wrote:</div>
I am assuming fuel injected, a disruption in power to the pump could be the issue. Make sure all grounds are clean and tight. Swap computers, etc. until the mis moves.

The ECM is the only thing we haven’t changed. Guess that’s next.
There a solid 12.5 + to the pump.

No clue what Jeremy said. LOL!

You need to do the test when you see the pressure drop, you could put the needle type voltmeter on it, easiest way to see a short spike, and run it that way once. It just sounds like something is cutting off the fuel, it could even be a bad oil pressure sender telling the computer there is no oil pressure and it shuts off fuel. Good luck.

The eprom is the little chip in your computer that has the vehicles calibrations in it. PCM(powertrain control module) ECM(engine control module). One in the same I guess just different names. I think the 454 were the last ones using that setup 1n 95-96

Might want to ask at https://www.chevytalk.org/fusionbb/showforum.php?fid/78/keyword/1988-1998_Chevy_Trucks/ as I think one of the moderators there had that engine in a few trucks

Since you have 2 engines, swap the ECMs and see if the issues follows from one to the other.

We used a different tank and had solid pressure.

Since we replaced everything from the pump to the engine, the fuel check valve was next in line going to the tank to take a look at.

The wire (upper right) you see in the photo is an aluminum welding rod! It was stuck in the check valve shown in the following photo.

Pressure is solid!! Motor is running great!

The tank/engine is 25 years old and NOW it coughs up a welding rod??

Thanks for all the responses!

Attachments:

1. 

   rod-in-check-valve.jpg
   

2. 

   Welding-Rod-and-Junk.jpg