Fuel trim "delay" in closed loop

[tttoon]

Sooo I've been stumped by this problem for a while now. When I have everything connected in my 91 318is with M50tu the engine seems to have a delay in the fuel injector signals. for example when I coast down to a red light and depress the clutch the rmps will oscillate 3-4 times from 1000-1200rpm before settling at 1050 rpm (give or take). Idle is not smooth then. When I drive part throttle (3000") on the freeway the engine sound will oscillate as well, as if the DME is constantly opening and closing the fuel injectors. Accelerating WOT the engine will oscillate as well.

When I disconnect the TPS (I think this forces open loop, right?) The oscillations disappear and the car seems to run better and pull somewhat harder. Idle is then low (600 rpm) because it disables the ICV I think. Idle is then noticably smoother than with the TPS connected

The specs are:

M50tu from '95 e34
413 silver label, non EWS DME. Tried with 2 different DME's but I bought the best running one second hand so I'm not 100% sure it's good, I would think so though.
S50 cams
21.5 lbs injectors
3.5" MAF
1 week old O2 sensor, did not make a difference
TRM chip for this configuration

Is there a DME wizard that can shed a light on this?

[samiam3356]

It comes out of closed loop at a certain temp. May be your temp sensor took a crap or you don't have things wired correctly. How hot does your motor get normally?

[tttoon]

Thats the problem I think, when it goes into closed loop. Temp sensors measured out to spec (bentley test) and the engine stays constant at 1/2 of the temp gauge. When it goes into closed loop and takes the O2 sensor in account it runs way worse than when it's in open loop (like forced open loop with the TPS disconnected)

[Zba]

Do you have any way to scan for codes?

Sounds like you may have a bad o2 sensor or o2 wiring. Do you have access to a multimeter? First check all of your plug connections and make sure they are tight, then check the o2 wiring. I would also check tps and maf signals.

After you unplug the tps and it smooths out have you plugged it back in? Does it start running poorly again, or is everything still smooth?

Will it smooth out if you unplug the front o2 sensor/maf etc or only with the tps unplugged?

Have you cleaned the throttle body?

Just a few things off the top of my head
GL!

[jrdeamicis]

Do you have any way to scan for codes?

Sounds like you may have a bad o2 sensor or o2 wiring. Do you have access to a multimeter? First check all of your plug connections and make sure they are tight, then check the o2 wiring. I would also check tps and maf signals.

After you unplug the tps and it smooths out have you plugged it back in? Does it start running poorly again, or is everything still smooth?

Will it smooth out if you unplug the front o2 sensor/maf etc or only with the tps unplugged?

Have you cleaned the throttle body?

Just a few things off the top of my head
GL!

The TPS should be 1k(ish) to 4k(ish) then no continuity @ WOT. Just use a multimeter and put it on pins 2+3 (If I remember correctly)

OP, start with what you know. It gets better when you unplug the TPS. Check your TPS.

[tttoon]

The TPS measures out fine according to the bentley spec, 1.2k to 4.6k at WOT. 4.2k across 1 and 3. 5DCV on the harness. The O2 wiring has been completely redone by me up to the harness, and checked out last week. O2 sensor is a brand new Bosch unit. I can't scan for codes, my check engine light does not work and the diag port doesn't power up a peake.

Upon more test drives, this is what I come up with:

-Everything connected: RPMs oscillate when depressing the clutch rolling to a stop, 3-4 times 100rpm around idle (1000 rpm). On the highway the engine sound audibly oscillates (I guess with the actual AFR)
-TPS disconnected: (it doesn't make a difference if I connect or disconnect the TPS with engine running or not): RPMs drop and stay steady at 700rpm, car "seems" to pull better.
If I disconnect the MAF the idle changes again, a slight hickup and then it seems comparable to TPS disconnected.

What I've been thinking: It seems that the ECU makes too big corrections in the fuel delivery to stay around stoich in closed loop. I'm wondering if that has something to do with the bigger injectors. I bought the car with a TRM chip supposedly for the configuration, but would simply puttting bigger injectors in a car that's not chipped for it give similar results?

And any tips on cleaning the throttle body? take it off completely and clean with alcohol?

[Tchao]

No, fuel trim adjustment will never be as great.
You most likely have a wiring problem if the sensors tested good.

It's not as simple as open/closed loop. Those are for long term fuel trim. Our ECUs don't use widebands.

You are running to default mode or safe mode, like when it looses a TPS or MAF signal.

Check all of your harness for pinches, rubbing, etc.


See if the local guys like Amr have an extra harness for you to barrow just to trouble shoot.

[Zba]

And any tips on cleaning the throttle body? take it off completely and clean with alcohol?

Run to the parts store for some throttle body cleaner. Take off the intake boot up to the throttle body, spray the cleaner into and around the butterfly valve to saturate the varnish, then use a rag soaked with the spray to clean the rest of the varnish. Don't forget to open the valve by hand and clean everywhere and be liberal with the spray, it works well.

I have a feeling it's pretty gross in there and I've seen instances where the turbulent airflow through there creates driveability issues.

BTW, are you saying the car surges?

[Adrian_Visser]

Why not figure out the CEL first and read the codes. OBD will help you.

I don't have any of my wiring charts in front of me right now to tell you which pin goes to which on the c101/x20 but I can tell you that you need to run power to pin 16 on the diagnostic connector to power up a peake.

You could temporarily run a wire from the + junction point in the engine bay to the diag. port pin 16 and get a code read right away.