E36 slight miss at idle, hard start No codes

[marcva]

My E36 is missing a little at idle, and it's a little hard to start (half dozen cranks). but I get no codes.

My mechanic ran a smoke test and found some slight leakage at the ASC throttle gasket. I'm replacing that and the throttle body profile gasket.

Is there any way to proactively test other components?

I would think
- idle control valve
- crank sensor
- Coils are reasonably new (30-40k on them).
- Injectors have been cleaned and benchmarked by cruzin (Didn't need it BTW).
- injector wiring?

- Fuel pump was done at about 140k. Fuel filter?

[bmwdirtracer]

Hi Marc,

It's not going to be the crank sensor. That causes no start, not hard start.

Coils tend to cause misfires at high rpms, or not spark at all. Fuel filter clogging would also cause issues at higher revs, not idle. A wiring issue's not likely to go away, off idle.


Cam sensor will cause a hard start, but not usually misfiring at idle. Still, it's a possible.

What spark plugs are you using, and what condition are they in? Oily? Smell of gas?

A leaking / failing fuel pressure regulator might be a suspect. A first check for this is to sniff the vacuum hose; the real test is testing fuel pressure, with and without vacuum to the regulator.

Is your air filter oiled? Is there any change in this behavior if the MAF is unplugged before starting? (This will, of course, set a code...do you have a way to clear codes?)

Do you have a way to watch live data for the O2 sensors?

Does this behavior change when the engine is stone cold, or warmed up?

[marcva]

Thank you for the quick reply, Chris. I hope you're doing well and that the E39 is holding up. or have you moved on to an E90m? (Seems a logical progression).

Responses
- Plugs are BMW. Whatever they recommend. I don't mess with that stuff
- Yes, My filter is oiled. I'll try unplugging the MAF, and I can clear codes. I can also watch O2 sensors with a bluetooth module that feeds my phone. I need to track down a stock air box one of these days.
- Seems the same warm or cold. Starting at the grocery store coming home not a lot better than when I first leave the house.

Further Hints/distractions
- One other hint is that the first time I turned the car on at idle this spring, it almost stalled. Then it recovered and ran OK.
- The battery has been disconnected within the last few hundred miles. Would there be adaptation going on? or does that only happen after codes are reset?

- Thanks for the injector assurance, though I had a flakey injector wire a few years back that a tech spliced with a replacement. I was wondering if its possible to swap out the injector wiring harness to clean that hack up, just for hygene's sake. It doesn't appear to be available separate from the main wiring harness.

Hoping the throttle body gaskets clean things up, though at 24 years and 189k. Its probably healthy to clean up other parts

Marc

Hi Marc,

It's not going to be the crank sensor. That causes no start, not hard start.

Coils tend to cause misfires at high rpms, or not spark at all. Fuel filter clogging would also cause issues at higher revs, not idle. A wiring issue's not likely to go away, off idle.

Cam sensor will cause a hard start, but not usually misfiring at idle. Still, it's a possible.

What spark plugs are you using, and what condition are they in? Oily? Smell of gas?

A leaking / failing fuel pressure regulator might be a suspect. A first check for this is to sniff the vacuum hose; the real test is testing fuel pressure, with and without vacuum to the regulator.

Is your air filter oiled? Is there any change in this behavior if the MAF is unplugged before starting? (This will, of course, set a code...do you have a way to clear codes?)

Do you have a way to watch live data for the O2 sensors?

Does this behavior change when the engine is stone cold, or warmed up?

[marcva]

rebuilt the throttle body with new gaskets as a smoke test highlighted a bit of a leak between the ASC and Main throttle bodies. Both old gaskets not quite as pliable as the new ones, and when I started and idled the car, it seems better in the driveway. We shall see when I drive it next.

Marc

[marcva]

Still missing. I should have cleaned out the idle control valve when I was in there. Also need to get some MAF cleaner. I have fuel pressure regulator on the way (and pump...cause 189k) I suppose I can pull plugs and look at them.

The hunt continues. More later.

[marcva]

Car seems to start ok, but develops an irregular stumble that manifests every 5-30 seconds when the car idles when warm.

Additional data points

Unplugging the AFM causes the car to stall, AFM readings on my OBD reader look plausible (they move with throttle, etc).
Definitely worse when warmed up The sensation feels like I have something building up, then detonating periodically.


Diagnostics by area:

INJECTORS
Injectors are freshly rebuilt replaced a bad injector a couple years ago, which lead to the refurb on the others.

Ive had injector wiring issues in the past that an indy solved by splicing in a new wire. I wonder if that hacked injector wire might be having issues. Can I test those with OBD reader? or do I have to use a multimeter? I notice the injector wires connect to the main harness at the fuel rail. Are those replaceable?

COILS PLUGS
Coils are newish
- I'll pull plugs (check for contamination that might hint at bad CCV)

INTAKE - Airflow.
- Clean AFM (though it seems OK) (Need to get a can of AFM cleaner)
- Clean ICV? (Should have done it when I had the throttle body off...
- [Replace CCV?]
- Try unplugging any of the other sensors to test?

Preventive work (Because 195k):
- Fuel Pump
- Fuel Pressure Regulator

Other items:

2- What should I watch for on my O2 sensors in the OBD reader? I see readings among the PIDs but don't know what to look for.



I have a can of 3M Intake cleaner I can run through the motor to clean up the chambers after I've looked at the plugs.

[dworthy]

Hi Marc!

Your pre-cat O2 sensors should fluxuate between .1v and .9v and that's when the car is at operating temps.

What Chris was eluding to on the "Oiled" filter is that they can foul your MAF, so be sure to clean it.

How's the gas mileage? What does your STFT and LTFT look like for each bank?

[marcva]

Hi Marc!

Your pre-cat O2 sensors should fluxuate between .1v and .7v and that's when the car is at operating temps.

What Chris was eluding to on the "Oiled" filter is that they can foul your MAF, so be sure to clean it.

How's the gas mileage? What does your STFT and LTFT look like for each bank?

Understand the implications of oiled filter and I watch that. I'll be cleaning it. Didn't grab the MAF numbers, but it seems to fluctuate properly with throttle application.


Mileage is down a little bit, though I haven't tracked lately, and living in a semi urban environment it moves drastically depending on how heavy my foot is. Id say about 19-20 which is fairly typical.

Data from my ACTRON OBD reader. observed in several minutes of idling at operating temperature.

O2 sensors

S11, S12 fluctuating between .13 and .98
S21, S22 steady at .97-.98

ST and LT FTRMS (Not sure if I'm readgin right.

ST ftrm 1 0%
ST ftrm 2 0%
LT ftrm 1 -7.7
LF ftrm 2 -7.8


ST ftrm 11 moves between about 3.1 to - 4,6 (?) dont have logging
ST ftrm 21 3.1 to -6.3

[dworthy]

Okay, so your STFT should be moving every second depending on how you are getting on the pedal. Of course they should not be in lock step, for they are two different banks. Your LTFT should hold steady and only really bounce around 1-2 percent on a normal drive. On the STFT I would be worried if they went outside the -20% to +20% and -10% to +10% on the LTFT. If you can data-log it with engine load so you can see how much extra fueling or leaning that is going on.

While it is somewhat acceptable up to 1V I would say that those post-cat sensors are a bit high. That might be worthwhile to have a closer look at too.

So here's a test you can do to see if it is adjusting properly:
At a stop pump the brakes. A lot
You should see the STFT go into the negative, and the more you pump, the lower it should go all the way down to -28 on both banks. This is a way to check to see how quick the oxygen sensors react, and the voltage should also follow as well.

[marcva]

Thank you very much for the insights. I'll try to get out and review some data after this next call. in about an hour.

Marc

[marcva]

Brake test:

- ST FRMs went to positive (?) 28 within 5-8 seconds, though It looks like my scan tools polling is every couple seconds.
- Voltages on O2 sensors maxed at 0.98 IIRC, they've been that way as long as I can remember. I used to run a bluetooth module and watched them when driving FTTT

[marcva]

Doing brake test again, it takes about 15 seconds for the ST to work their way up with rapid brake pedal pumping.

[marcva]

Is this a sign of oxygen sensor's going bad?/contaminated?

[dworthy]

I think so, for when you pump the brakes, that should cause it to go rich, thus making the STFT to go in the negatives. That's how it's supposed to happen is the air is being expelled out by the booster, but it is being metered at the MAF as entering the motor, so you have less air entering the combustion chamber. When the Oxygen sensors see this, it should be cutting the fuel trim down not up if that makes sense.

[marcva]

But no codes for 02 sensors... Do I have to replace all 4? or just the first two? Are there offline tests? Or will I just see filthy, contaminated o2 sensors when I pull them and know?

Marc

[dworthy]

They should be a sand color and uniform all around the probe. If you see black sooty color, then for sure it's running a bit rich. Most of the time BMW recommend replacement IIRC every 60k miles on the S-50 motor, and you should do all 4. Once they get replaced, make sure you reset the adaptation for the oxygen sensors. As those post-cat sensors are a bit high, you could be looking at a rich function.

Again not 100% sure this will be your issue, have you checked the fuel pressure yet? Like Chris noted check the fuel pressure regulator block next to the fuel filter?

[marcva]

Have not checked fuel pressure as I'm about to do some general maintenance. Will replace fuel pump, pressure regulator, icv, ccv. Check plugs and O2 sensors. Other than plugs, all original @ 190k, and I'm about to drive 800 mi cross country. Cleaned MAF, though it wasn't dirty before I started spraying. People comment about layers of soot and oil. I didn't see that.

Miss is small, but I notice small things after 24 years with the same car.

[dworthy]

I know what you mean, as be the original owner of the wagon, I noticed that something was off a while back. That was a rabbit hole, but in the end I think that I won't have any problems for another 5 years out of that car.

[marcva]

Update. Replaced the fuel pump and the car seems to idle more smoothly. perhaps I had nominal fuel pressure. I'm going to continue the overhaul later this week with pressure regulator. Idle Control Valve and Crankcase vent valve along with associated hoses. I'm hoping this should finish the overhaul cycle and clean things up. I'll reserve judgement on the O2 sensors until the other money is spent and do those next if needed.

Marc

[dworthy]

Are you just throwing parts at the car Marc? Well in a way at your mileage it would just be due anyway if you think about it.

[marcva]

Sorry, back again after my relocation. Yes, I threw some parts at the car, but they were all long overdue maintenance items. After 24 years, the car didn't owe me anything. I ended up doing the CCV and the icv. The CCV was cracked and probably jerking a bit. The icv was not that bad and might have been good with a clean. The car runs well and generally idles fine, though it misses *every once in a while.* At this point I'm doing local shorter trips. I'm going to watch and wait for now. Hoping that I'll get a definitive code to confirm the next tweak.

[dworthy]

As the Germans say: "At 24 it's still a young timer!"

I would say short of yanking the engine out and inspecting every cable, just wait until it does come back and check for codes.

[ross1]

Forgive me if already addressed but long crank times are quite often due to poor fuel pressure.
Is the starting problem only on first start of the day or standing for quite a while or always?
I'd check pressure after standing. If significantly below spec (3 bar?) the pump, regulator and injectors are all suspects for allowing pressure to bleed off.

[marcva]

Thanks Ross1. Starting well now. Pump, regulator both new and injectors cleaned and indexed within 20k miles.

In summary over refreshed just about everything except O2 sensors, and I could peek at the plugs though they only have about 50k on them.