Intermittent loss of power (1 Viewer)

[Mayh3msHand]

Good afternoon to all.

1996
255k
All OEM parts

I have been having an intermittent loss of power. He will run well for 3 or 4 days, then one day while driving he will suddenly bog down and lose power.

When this happens, the temp goes up anywhere from 15 to 25 degrees F. He will not go above 50 while floored, shifting becomes very rough. When floored to the point to force a downshift, he will downshift, the engine will shoot up to 3500 rpms but the speed will drop and he slows down. My fuel consumption drops to about 6 to 8 a gallon, and the engine acts as if it has been severely retarded.

No codes

I've checked O2 sensors, brand new, along with all wiring all the way up to the ECU.

I've replaced with brand new cats about a year ago, and have checked Temps from both.

I have checked all wiring from the distributor and fuel injectors including through the harness.

MAF has been checked along with all wiring.

EGR and EGR diaphragm has been deleted. Plate blocked and resistor installed.

Knock senors have been checked along with all wiring.

About a 6 months to a year ago he was completely gone through on the top end side. Head gasket, valve seals, water pump, thermostat, flushed radiator etc. Timing has been checked and he is advanced 5 degrees.

Again, this seems to be intermittent. And very frustrating. I have school bus drivers giving me the finger when I try to pull into traffic. He simply will not move.

Any and all help is greatly appreciated.

 

[Mayh3msHand]

UPDATE:

Brand new wiring harness has been installed. No change to rigs behavior. I plan on moving to the ECU next.

The behavior is no longer intermittent. It's a complete loss of power, slow acceleration, and will not go above 45 mph.

Anything above 2000 rpms will send the motor into overheating.

 

[gummycarbs]

I know you said that the head gasket was done, but I'd still do a coolant test just to be sure.

he will downshift, the engine will shoot up to 3500 rpms but the speed will drop and he slows down.

Are the RPMs going up and down consistently with speed? Is there any reason to believe that any part of the drivetrain is slipping?

My first thought was throttle position sensor, but that wouldn't explain the heat increase.

 

[rdcnj]

I had this happen, in my scenario it was the EGR valve that ended up resolving up.

Mine was slightly more consistent where it didn't rely on temperature, but would induce a "hard stall" at the most random times.

"Anything above 2000 rpms will send the motor into overheating."

This is bad and if you had the headgasket done recently, I would be checking with that shop.

 

[Irish Reiver]

I had this happen, in my scenario it was the EGR valve that ended up resolving up.

Mine was slightly more consistent where it didn't rely on temperature, but would induce a "hard stall" at the most random times.

Are you able to expand on what the issue was with your EGR.

 

[rdcnj]

Are you able to expand on what the issue was with your EGR.

Pretty sure debris got in there when we were reconditioning the vehicle.

I had replaced the EGR valve due to a "suercharger" like whine coming from the truck after eliminating a few other variables.

What I noticed is that since the EGR valve was replaced, the symptoms mentioned here completely disappeared.