K-jet rough idle and hesitation

Here's the setup '85 245 turbo has been sitting for a few years due to holes in block, picked it up for $200, put in early b21F block with the FT head, known good fuel dizzy and CPR from '82 turbo, 90+, 19T, npr, b21F intake, brand new injectors.

it had a nasty fuel leak on the return line to the tank, so i cut it, flared it, added an extra foot or so of fuel hose.

so, it being an early b21F block, there's no provision for the thermal cutout switch or the CIS coolant temp sensor. I made a hole in the head for the CIS sensor, and doing some reading, it sounded like the thermal cutout switch wasn't super necessary. leaving the female spade for the cutout switch disconnected, it would take quite a bit to get it started, keeping up on the gas til it warmed up and hit (i assume) closed loop. it idled okay once in closed loop, but there would be a hesitation under light throttle around 2k-2.5k.

So doing some experimenting, i ran a wire from the cutout spade to ground, and it ran a lot better, no hesitation, smoother idle, etc. aha! i thought to myself, the plug on the passenger side of the engine by the WP and oil pressure sensor is the exact same thread pitch as the cutout switch! how serendipitous! so i installed the cutout switch there, ran a wire from the spade to the switch, and am now having the same issues as having no switch or ground at all. i'm guessing it's not normal operation to have the cold start injector on all the time.

also, after sitting a while, it takes a couple tries before it will stay running, when warm it'll start right up no problem. possibly an issue with losing residual fuel pressure? possibly related? not sure. any advice is welcome.

Typically, the thermal cutout switch keeps the engine in open-loop longer than it would with the switch disconnected. Maybe lazy O2 sensor? I have the switch disconnected on my 245Ti and it starts up very quickly and idles fine when stone cold. I am still running the stock exhaust manifold with the sensor threaded into the bottom, so it gets warm quickly. Maybe a 3-wire sensor would be a good upgrade.

The thermal time switch (installed at the rear of the head, next to the #4 intake runner on a non-turbo head, or under the #3 runner on a turbo head) controls the cold start injector. If that's bad, the cold start injector won't turn on when cold, and may stay on when warm, instead of being controlled by the impulse relay.

A car that has been sitting and resurrected with kjet should have the pressures checked. Your description seems like typical incorrect control pressure. The residual pressure is controlled by the
check valve in the fuel pump and the fuel accumulator. The control pressure regulator or warmup
regulator directly affects the mixture from cold till fully warmed up.

I disconnected the cutout switch and have had it connected and it warms up fine with or without it in my experience. You should also make sure the cold running enrichment is working. That minimizes hesitation while driving on a cold engine. 85 and 82 used two different methods of doing that.
You want to make sure you are using one of them.

It’s got a brand new Bosch o2 sensor. I’ll try to build the $20 tbricks kjet pressure tester.

In the 20 years I've owned my turbo. I'm on it's fourth control pressure regulator. Each death follows.
1st one clogged. This was the 'problem' the car had when I bought it in 1995. original 079 bad
2nd one blew up under boost and started leaking from the vent hose. Was a new volvo 123 unit
3rd one leaked from the vent hose. The difference in the leakers was the previous one actually
made a popping or bursting sound and died. This leaker was quiet. rebuilt 079

This fourth cpr is another rebuilt 079 has been in there a few years. I think that the leakers were caused by alcohol in the fuel. But it is conjecture. Suffice it to say that it has been the most replaced part of the kjet system in my car. In 20 years I have replaced a lot. lol.

My experience with CPR (WUR) devices is far simpler. Cleaned a couple. They are very simple devices. A pressure disk blocking a fuel nozzle with a spring regulating the flow adjusted by a heater element and vacuum.

Testing the heating element resistance which is just a few ohms will find most functional.

Cleaning the fuel screen and cleaning the disk and nozzle is most of the remaining problems.

Since there is nothing but steel and aluminum in the fuel flow I cannot see anything to be affected by alcohol.

Trash affecting the regulating disk to nozzle were both my problems.

finally got around to building a pressure tester (more like $30) and noticed the pressure did not change at all between system pressure and control pressure. so, i happened to have another CPR laying around. turns out, running a 140 CPR on a factory intercooled turbo car, like you would on earlier turbos (delay valve) is not the way to go. did a little reading, swapped a 128 in, ran the thermo wax valve line to the correct place, adjusted the dizzy slightly, idles smooth, no more hesitation, control pressure is well within spec. still a bit of a rough start, but i've got a new fuel pump check valve on the way, and i think that'll help. residual pressure tanks pretty quick.

Hmmm, which car did the 140 CPR come off of? I currently have my factory intercooled 245Ti running just fine with the 079 CPR that was installed on the B21FT I installed in it last summer. I did disconnect the pressure differential switch, so it's no longer an '84 car with that and the 128 CPR that all 1984-85 240 Turbos came with, even the non-intercooled cars.

-J

I bought the 140 several years ago for my ‘82 turbo. Not sure what it came off of, but it had the same vac line nipples that I needed for that car.

But now I’ve got my ‘85 hooked up like an ‘85 and it seems to work