Bad fuel pump check valve

[IMSAracer944]

87 944 Base, engine cranks up and idles perfectly, once warmed up it starts loosing power at 2,000 rpm, by 3,000 it’s done. Have replaced fuel filter, TPS, air meter refurbished and calibrated, replaced fuel regulator with no change. Did a fuel pressure test and found the check valve leaking down in just a couple of minutes. Does anyone know if this would cause the acceleration issue?

[944 Ecology]

Probably not, but replacing the check valve certainly would help with hot starts (fuel will vaporize in the rail with residual heat.)

I would put a fuel pressure gauge and monitor the fuel pressure while the problem is occurring.

[kdjones2000]

You sure it's not something due to the speed/reference sensors?

[walfreyydo]

Does it stutter or hesitate between 2000-3000 rpm?
https://www.clarks-garage.com/shop-manual/ts-01.htm#stumble

[Monkey Wrench]

just a "maybe" but you could check that the screen in the tank isn't blocked, causing fuel starvation. there are also little filters in each injector , perhaps those may cause other issues if they plug. the injector parts are cheap or there are places that can clean and bench test them for you, examine the spray patterns. some people exchange or send out or replace or clean them by themselves.

if you are extremely cautious and careful of the fuel and fire issues.. do it outside and with a fire extinguisher rated for a fuel fire, and a cold engine and all the other logical precautions...

you can pull the injectors and entire fuel rail to observe how well they shut off with the key turned off . If they don't seal and continue to empty the fuel rail after key off, then that can cause the pressure to not maintain. if that happens you may also see white smoke on startup or maybe one carboned up plug.

on mine and likely yours there is a thing near the fuel pump that contains the check valve , you can probably replace it for not much but it's probably just a spring and ball so cleaning it may be enough. bit of dirt may be preventing the ball from sealing against it's seat. there are some differences in the fuel system that depend upon year.

using a fuel pressure gauge makes sense, if the in tank fuel screen is blocked , pressure would drop.

could also be that the engine shakes or twists or moves more at higher revs and maybe that affects cabling to engine sensors.

in my volvo I had an issue where a injector was not closing, it was emptying the pressure from the fuel rail into cylinder 3 upon every shutdown. I was confused until I observed it. a mechanic may have found that by other means that do not require spraying fuel around and the dangers of doing that. Perhaps by swapping injectors. I found that once I looked for it that way, so I could actually observe, then it became obvious.

[paulzebo]

944 Ecology and Monkey Wrench are correct. the Check valve is only for startup to have instant pressure at the injectors. A bad check valve would have a slightly longer start up time. On the other hand, a sticking fuel injector will make the engine run lean. The stuck injector allows too much fuel into the engine and the computer will try to lean all 4 of the injectors out. Until it's too lean and cannot run on that one rich injector. Techron is one additive mixed with fuels at your station. But only if the station has Top Teir Fuels. Premium has more of the additive precisely to keep those injectors clean. The good news is you can buy it separately or the fuel injector cleaner of your choice. The bad news is it won't be an instant correction and takes time. Removal of the injectors and a good cleaning at a business who specializes in injectors will be the only immediate fix.