I have checked all the sensors,put on new gaskets(intake,exhaust and throttle body)checked all vacuum hoses.Put in new plugs,distributor cap and rotor and plug wires.
What I have found out is that in Open Loop for about 5 to 8 min. there is no miss or pop out the tailpipe. As soon as it goes into Closed Loop that is when it starts. So what comes into play when it goes into Closed Loop?

I would check the fuel pressure. Before the O2 sensor is called in to tune the mixture, injector duty cycle is longer and the mixture is on the rich side. This can mask low fuel pressure. Once the sensor takes control of the mixture, low fuel pressure can result in misfire as the fuel is not well atomized and doesn't fully combust.

Fuel pressure problems could be the result of a bad regulator or a failing pump/pumps.

o2 sensor takes over in closed loop. good luck, chuck.

Is that the only thing? Because that's new.

you don't say what year. no 240 really has a closed loop. and the brand and type of o2 is relevant, also. cheap 1s don't do well in every car. i only use the bosch and oe connectors, no splicing allowed. cheap also applies to the ignition system. you only say replaced, not with what. need to know because i can't see under your hood, the light here sucks.good luck, chuck.

It's a B21ft 85 244. Ignition parts are Bosch,Bosch oxygen sensor,wires are Volvo OEM bougicord. Did fuel pressure test- System Line Pressure 80psi, Control Pressure 50psi,Rest Pressure after 20min.38psi.

I thought '85s had the B230F engine.
Dukester

only the 240t had the b21ft in 85. everything else was b230. and so it goes, chuck.

85 kjet exhaust backfire USUALLY means running rich. i trust the cpr is correct at the correct temps-50 psi sounds right for fully warm. no rest pressure just means long crank, usually not a running problem after starting. did you test fuel press while it happened?

if you unplug the o2, does it go away? is the freq. valve buzzing when o2 is plugged in? is it even, that is on-off-on-off, not onnnnnn-off-onnnnn-off or the other way around? have you driven it enough to notice a mileage difference between o2 plugged in or not? have you watched the o2 while driving?

injectors leaking? gotta pull them and check with fuel pump running. more than 100k? they're worn out.

i'd also look at the coil's reserve kv with an ignition scope. not enough spark looks like too much fuel. in this case, the coil's a long shot.

how's the engine harness? could be the o2 ecu isn't talking nice because of flaking insulation you can't see. luckily, it's not a bad rebuild. much fewer wires than an lh car.

out of ideas. good luck, chuck.

Engine harness replaced with newer type.
Injectors all new 1 yr. ago and just checked not leaking nor start injector.
Oxygen Sensor unhooked still pop's.

When I unhook Oxygen Sensor and I adjust the Air Flow Sensor to it's best idle the popping stops. I think I'm making it richer(clockwise)not sure though.

adjusting co when cold or warm? gotta be warm. if you have to richen it to idle correctly and then it pops in the exhaust, i swear it's too rich. BUT, turbos always needed to be a little richer to idle ok. maybe a vacuum leak somewhere that the rich adj at idle covers up. intake gasket cracked? brake booster leaking? intercooler and hoses intact?

did you open the injectors when they were out? maybe 1 is opening too soon.

have you checked the test point with a dwell meter?

this manual has a good section on tuning with a dwell meter-

http://www.k-jet.org/files/greenbooks/TP30163-2_engines_b21_b23_part_2.pdf

you're sure the ignition isn't dropping out causing the miss?
not sure. good luck, chuck.

Yes I checked the injectors by lifting the air flow sensor plate.
Used the test point with dwell meter and adjusted when warm.
Checked No vac leaks anywhere. Vac running 18psi.

This is driving me crazy. I have another 128 control pressure regulator (don't know if it's good) but will try it Monday when I'm off work. There is a guy on T.B. that knows how to set them up so if the one I have doesn't work I will send it to him.

whatever the answer, let us know, please. good luck, chuck.

Thanks for your help,I'm running out of things to try but I think it's something fuel related.

i'm not convinced. had a 960 once that would miss that didn't feel like a real miss, under perfect conditions-easily duplicated-that occurred when trans went 3-4. boss says needs a trans-wasn't it. boss says needs a trans ecm-wasn't it. got out the scope and looked at the ignition when it happened. #4 dropped off at the same time, every time 3-4 was happening, etc. just enough load for the scope to catch it. #4 plug was cracked. not knowing the conditions yours is occurring nor the results of fuel press. during the incident, o2, etc., it's really hard to tell from here. i'd be REAL suprised if a different cpr does it. testing control pressure while driving can prove/disprove it. maybe the vacuum to it is wrong or bad-dunno.

something is changing under those conditions-i just can't tell you the 1 thing without more testing. good luck, chuck.

I understand but I don't have a scope. You said vacuum to control pressure regulator but mine doesn't have vac.lines it's a 128 only used on the 1985 B21ft.

If I disconnect O2 sensor and adjust the fuel mixture to it's best setting by ear there isn't popping and idles smooth.It also runs fine on the road without missing. Well I will try the new/used CPR on Monday and also recheck fuel readings.

I didn't have time today to try the other CPR or retest the fuel pressure. I hope I can do it Tuesday. I will post the results.

I got a chance to check the fuel flow at the injectors and found 3 injectors with poor spry patterns. I had bought 4 injectors from FCP at the beginning of the year pn# 0437502015 but they sent 0437502023 and said they had the same specs. as the 015's so I used them.
I called them yesterday and they are sending me 015's.
FCP always makes good on there parts return and I thank them for that.
I can't say for sure that the injector's are causing the miss so I will have to wait and see until I get them.

Thanks for the feedback on your car. Apparently I was not the only one not familiar with the letters and a B21 in an '85.

Iam not home with my Bentley book or my 78's green books but 50 psi control presure does seem to me to be too high.

As I remember the injectors run in the neighborhood 32+ psi in order to open. There is a maximum but I forget that one. Each injector is feed by perimeter pistons slots of the fuel distributor that pretty much regulates volume along with the frequency valve per orders of the ECU and the O2 sensor.
The whole setup is like a mechanical AMM thas on the LH system.

The contol pressure regulator controls the flap hold down pressure during cold to hot operation so it should vary in pressure from its own internal electric heater.

I would think the control pressure is probably only a few psi more that the controlled injector pressure. Someone might be able to find you that exact range of specific psi tolerance.

On the pressure testing hose setup you should have three separate readings. Line from the pumps, the flap control pressure and the injector pressure.

I found it interesting that you know someone who recalibrates these regulators too.

I have read that in most cases its a little wear around the heater fulcrum or a dirty filter screen or two that gives them hee bee jee bee's! Their so reliable its got to be a minor repair if you have parts or skills.

Probably the same with the LH's AMM's. Isn't that always the case?

I have seen where dealers try to get hundreds of dollars for new ones. I doubt Volvo paid out great amounts of money for them in quantity or we would not have even able to afford the car at their low production levels. Bosch probably put them on many makes or systems at the time.

I would like to add that if this does lead to any resolution, you might try changing the spark plug gap a little tighter by a few thousandths of an inch.
I have found that on some lean burning cylinders or oil fouling cylinders the decrease helps. Just in case there is a blowing out of the spark or fouling to ground under either condition.

Good luck tomorrow.

Phil

Is this B21F with a "T" mean it's a turbo?

By any chance is this also a CIS injection system with Lambda?

If so, it might have a Frequency Valve under the brake booster. Is it buzzing all the time like it has too!

There is a relay that controls the O2 sensor and the operations of FV.

It's a square cube relay on the front left fender by the headlight dipper relay.

Swede Freak spoke of mixtures and I saw a "control" pressure you noted.
That's what prompted so many question on my part! I agree with his scenario.
You might listen for a smooth even buzz of that valve as it might have a problem not related to a relay?


My relay failed from corrosion and old age, take your pick.
Mostly hard start problems at random though. Ran rough from a bad mixture.

Phil

Yes T means Turbo
Yes CIS Lambda
No F.V. under brake boaster
Checked relay for Oxygen Sensor-Tested Good
F.V. is on top of Fuel Distributor and buzzes on and off like it should.
Oxygen Sensor connected engine running .45 to .51 volts

I'm leaning towards the Fuel Pressure Regulator. Isn't Line Pressure Fuel Pressure? 80psi?