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240 81 Kjet B21F Running rough with warm start

VikingLlama

New member
Joined
Mar 26, 2022
Location
Bellevue, WA
My volvo runs fine when it cold starts, then continues to run fine after it heats up. But as soon as I turn it off and go to turn it on again when it's warm, it starts to run really rich and start backfiring under load or really lean and almost stall out at idle.
So far I've
  • Checked and gapped sparkplugs
  • Replaced Injector Seals and O-rings
  • Replaced the Fuel tank pump
  • Replaced Fuel Filter
  • Replaced one cracked vacuum hose and have been unable to find any other bad hoses.
  • Took out the preheat hose and valve inside airbox
  • Replaced Exhaust from downpipe back

There is a blue port with a spot for a vacuum hose sticking out the driver side of the engine block underneath the intake manifold, have no clue where it would connect to.
It does currently have an exhaust leak at the gasket connected the headers to the down pipe since I apparently got a bad one when replacing my exhaust and I haven't replaced it yet. But I wouldn't think it would cause issues quite as bad as this

Any ideas appreciated, thanks.
 
Last edited:
Look for a hose that's coming off the control pressure regulator, at the bottom. There may be a missing vacuum line, hence the open port on the thermovalve.

vac-B21FT_CPR.jpg


From dbarton's website...
 
Look for a hose that's coming off the control pressure regulator, at the bottom. There may be a missing vacuum line, hence the open port on the thermovalve.

vac-B21FT_CPR.jpg


From dbarton's website...

Thank you so much, mine currently does a loop at the bottom with a vacuum hose instead of going to a delay valve or to the thermostat valve
 
The vacuum hoses to the CPR only affect cold running enrichment (if the thermostat valve is working correctly) so I doubt it's causing your hot starting problem.

You really need to get a fuel pressure gauge to know what's going on with the fuel system.
 
My thermostat valve wasn't hooked up at all, also realized it had one of the ports broken off, sourced a new one and now it seems to have fixed the issue, thank you guys for the help!
 
https://photos.app.goo.gl/1nvPaBKTAkp83nfZA

Update, has started acting up. Still running better after hooking up a new thermostat to the warm up regulator.

Now its starting to misfire and stall after getting warmed up.

Have not been able to find a fuel pressure tester (it doesn't seem like the orielly's rental would fit, any experience?), need to get a multimeter with dwell to see if co is anywhere close, how worried should I be taking apart the fuel distributor, my co adjustment has the steel ball blocking it?

Pics included have a video of the engine symptoms. also found those 3 wires unhooked, unsure if any of those are needed for anything, however the one that seems cut and goes to the bottom of the block next to the trans seems like it would be important.
 
The cut wire is for the factory mono tester. You don't need it.

The single wire connector near the dipstick is for the starter. Apply power from the battery to activate the starter. Make sure the car is in neutral if you have a manual trans.

I believe the connector with the green and black wire is for cruise control.

I have the factory fuel pressure gauge and adapters for rent if you can't locate one locally.
 
Yes, but kjet isn't rocket science either. It's like magic because it takes studying the information. (your magic grimoire.) Understanding it, and getting the few tools needed to perform the magic. (Your wand so to speak.)
 
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