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Volvo 240 B230FT misfiring when warmed up

J

Joss

Member
Joined
Feb 28, 2023
Location
Estonia, Tallinn
Hi,

I have a problem that the engine starts misfiring after it gets warmed up.
When I first run the engine it idles and runs good, I see that my wideband shows about 12.5AFR, whenever it gets warmed up the wideband jumps to 14.7AFR and the car starts to misfire. I noticed that when the misfire happens the AFR jumps from 14.7 to 16.

I have tried
  • Changing rotor and cap
  • Tested and changed ECT, Tested the ECT itself when it was new and out of the engine and tested from the ECU pins after it was installed
  • New spark plugs
  • New spark plug wires
  • Coil changed with known good one from my other car
  • Power stage changed with known good one from my other car
  • ECU changed with known good one from my other car
  • Fuel pressure is at 2.1bar (Edited, just measured again)
  • Tested for air leaks, could not find any
  • Vacuum test was good
  • Timing is on point, tested with the light
  • Engine idles at about 900RPM
  • Idle valve is tested and is brand new from skandix
  • I also tested with the 025 MAF and Green Giant injectros, 025 MAF and normal turbo injectors, 016 MAF and green giant injectors - still resulted in misfire after warmed up.
  • There does not seem to be excessive pressure in the coolant hoses
  • New fuel pressure regulator
  • Has Walbro 255 in tank fuel pump, no under body fuel pump. Was bought 3 months ago.
  • CPS changed with brand new

I hope I did not forget anything that I've tried already.

Added the original pump in between the fuel filter and fuel rail/fuel pressure gauge. Fuel pressure is now at 3bar but it still misfires.
 
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When you put new plugs in did you set the gap? Have you looked at the quality of the spark? Is it orange or blue/white? What is the condition of the air handling hoses? If any are oil soaked and squishy that can act like an air leak. Check along the seams of the intercooler between the grid and the side tank. If there is moisture along the seam it's leaking air. Verify the crank pulley isn't slipping.
 
The jump in AFRs is likely because of the misfire, not the cause. When there's not a complete combustion, oxygen will make it into the exhaust. Since 14.7 is healthy, I'd look at ignition. I agree with Dave, check out the plugs and do a compression test when hot.
 
I forgot to add compression numbers.

Cold
1. Cylinder 8bar
2. Cylinder 9bar
3. Cylinder 8.5bar
4. Cylinder 9bar

Warm
1. Cylinder 8.75bar
2. Cylinder 8.5bar
3. Cylinder 9bar
4. Cylinder 9bar

I have never learned how to check quality of the spark, how do you do that? Remove the spark plug cables, put them near ground and just observe the color?

I have checked all the air hoses, they seemed fine. I will recheck, just in case I missed something.

I also tried different ICU from the other car, just in case - it changed nothing.

When observing the crank belt I cant see it slipping, but maybe there is a better way to test that. I changed the belt last spring and the car is only driven in the summer, so it has seen very few hundred KMs.

EDIT:
I feel quite stupid now, I never thought intercooler as part of the "air intake", I dont know why, its so obvious. I also have some moisture there I think and I cant remember spilling any liquid under there. I think I have at least one clue to follow now, I will take out the intercooler for inspection.

EDIT2:
Its oil, but I think Its from my oil catch can when It leaked. Will test the new intercooler just to be sure.

If any are oil soaked and squishy that can act like an air leak
Click to expand...
I have cleaned the air hoses previously from oil, they seemed fine. If I dont get it fixed soon I will buy the smoke machine.

EDIT3:
Tried new old intercooler, did not change anything. Sprayed break cleaner inbetween every air connection and it did not change the RPM at all.
 

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Did you gap the plugs? .028" or less, I usually have to close the gap a little on new plugs.
Click to expand...
I have never gapped them, but they came gapped at 0.037''.
I will try gapping tommorrow.

I see the car is green, so it's been LH2.4 swapped. How is the power stage being mounted? The base it's on works as a heat sink.
Click to expand...
Power stage is mounted on the original plate. I also re applied the thermal paste last summer.

The car was originally B19A, carburetted engine. Now its running LH 2.4 B230FT with 16t turbo and original injectors, 984 ECU and ICU. currently non-chipped. It has been running good after the swap for two years, without any issues whatsoever. It started acting out about a month ago.
 
Have you checked the color of the spark when you are having the misfire? So with a warmed up engine. Shut down and do a spark check. I've had coils that get a weaker spark as they get warm from use. I've also had ignition amps that shut down or misfire when hot.
 
dl242gt said:
Have you checked the color of the spark when you are having the misfire? So with a warmed up engine. Shut down and do a spark check. I've had coils that get a weaker spark as they get warm from use. I've also had ignition amps that shut down or misfire when hot.
Click to expand...
+1 on the ignition amps i've had this happen to me too was a massive PITA to figure that one out
 
Had white spark on cylinder 4, 3 and 2.
Yellow on spark plug 1. Changed spark plug 1, now all spark plugs are sparking white.

Weird thing is, when I pulled the injector plug, it started to run on 3 cylinders, as expected. But when I plug the injector back in, the RPMs rise and while the RPMs have risen the engine is silky smooth. After 15 seconds or so, the computer "resets" to default again and it starts misfiring.

When I give it gas while everything is connected, it still misfires so I think it's not directly related to RPMs.

Not sure if its important but injectors have 2.3ohms resistance and its connectors have 9.3 ohms resistance.

I also found out that there is connectivity between each injector ECU wire and resistor ballast number 3 wire, as far as I know the injector ECU wire should not be connected to the resistor ballast. Each injector 12v wire should correspond to one resistor ballast wire, the ECU wires should not have connectivity at resistor ballast.
 
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Im back in the beginning. It was not the wiring. I also tried changing lambda, did not change anything.
Does anyone got any more ideas what to test for?

I will try to get the smoke tester in the upcoming week.
 
Joss said:
Im back in the beginning. It was not the wiring. I also tried changing lambda, did not change anything.
Does anyone got any more ideas what to test for?

I will try to get the smoke tester in the upcoming week.
Click to expand...
Having a very similar issue, following.
 
In one of the evenings I swapped my lambda and rotor. Tried the engine, it still misfired.
Came back the next day to just give it one more try, no more misfires. Swapped back the lambda to the old one, no misfire. Swapped the old rotor back, still no misfire. And hadn't had no misfires since.
No idea why it misfired or why it stopped misfiring.
 
Possibly there was moisture stuck in the distributor cap? O2 wiring can have issues, the wire is shielded and if the .5V bias signal gets pulled to ground by touching the shielding it will pull rich? Sometimes if you don't reset the ECU between fixes it will run poorly because it has adapted to the issue.
 
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