300sdl won't rev past 3k under load

[chuckfryer]

Hello-
I have a 1987 300sdl. It's acting very strange, it revs freely in park with no load. It takes off from a stop fairly well, the 1-2 shift occurs over 4000. After that it won't go past 3K. Boost is at 14 PSI until it hits 3000 then falls off. I have replaced fuel filters, swapped out alda, even took the Alda off for a test drive no change. This may be pure coincidence but I will tell you anyway.it started happening after I put a new thermostat in and replaced the three prong coolant sensor at the upper radiator hose. Please help me get this car back to being drivable.

Thanks

[speednjay]

Check the exhaust maybe that catalytic converters is plugged

[tyl604]

You could try step by step reverse engineering. Start with putting back in the old three prong coolant sensor. (Just guessing.)

Could the switchover valve on the firewall have just suddenly clogged up or dropped one of its vac lines?

[chuckfryer]

Ok, I put old 3 prong back....no change. I don't have a cat, it's all pipe not even a muffler. Overboost already bypassed. All good ideas though, thanks.

[Dubyagee]

Sounds like a fuel blockage or a failed lift pump.

[Diseasel300]

The fueling is entirely mechanical, there's no sensor anywhere on the car that will affect the fuel delivery. Check your accelerator linkage and make sure when the pedal is floored that the rack lever on the back side of the IP is against its stop.

[oldsinner111]

for a diesel always for me,tank screen,or main filter. Weak lift pump,I would use cheap electric pump,to save from buying lift pump

[chuckfryer]

Ended up being the intake path. While replacing the thermostat I removed the air cleaner assembly. While it was out the filter was dirty so I blew it out, and ordered a new one. I removed the old filter completely and car ran like it should! problem solved