Dillon93dillon

motor im working with is a 2000 silverado 5.3l drive by cable.
swapped into a 1979 chevy k20 truck.
mated to a th350/203

the problem im running into here is whether the motor is hot or cold, when i start the truck, the idle shoots way up to 2000 rpm, for about 30 seconds, then gradually comes down to 1500, and over a period of 2 minutes or so it will settle at 800 when its warm.

Update: also found i had two codes that just came up the other day, truck was running great besides the idle issue, then on my way home just before the house i got check engine light, p0172 and 175. both banks are to rich.

My brothers laptop (autotap hookup) is telling me desired engine speed is 600 rpm, which im not seeing.
i believe it was the IAC or MAF counts were reading 0 at idle is this normal?

and my dakota digital VSS converter is reading 6-9 mph just sitting still in park.

i have replaced intake gaskets thinking it could be the problem, but cant find a vacuum leak.

did some work on the scanner today, found out, those two codes, MAF was reading around 11.8 lbs? dont remember what scale it was reading. vss was reading 3-5 mph,
Bank one was reading -15- -19 % i believe
Bank two was reading -15- -31 % ( smoking only on bank two)

I wouldnt think this would be a vacuum leak considering that the ECM is trying to lean it out, but not doing so great. (at running temp). if it was a vacuum leak i would think it would be a lean condition not rich.
any input would be appreciated. thanks

3.4camaro

iTrader: (1)

So in open loop, it doesn't listen to idle commands. Once it warms up and goes into closed loop, it starts listening to the oxygen sensors and smoothing out the idle. I believe in open loop it just takes data from the MAF and fuel table, without making fuel trim corrections.

Sounds like a MAF issue to me, although I don't know what to make of the VSS reading.

Dillon93dillon

yeah, ive heard of the IAC could be screwing with it

Steve Bryant

iTrader: (1)

Dillon93dillon,
I moved your thread over to PCM Diagnostics & Tuning because it really isn't the sort of subject that Advanced Engineering is set up for. When in open loop, the mixture (AFR) is based on a blend of the Mass Airflow (MAF - most of the time) and the Volumetric Efficiency Table (VE - during throttle/RPM transitions). Once your engine warms up to the closed loop enable temperature, the long term and short term fuel trim start to bring the AFR back toward 14.7. I suspect that your MAF calibration is not correct for your conversion installation, but it could be something else.

Steve

Dillon93dillon

the truck ran fine days ago. the tuning was done professionally, and im now getting in spec MAF lbs per min readings.

but i see that bank 1 sensor 1 is reading .050 voltage to .850 or so. but bank 2 wasnt altering voltage very much. .790-.890 or so was all. way rich, and cylinders 3 and 5 are puking fuel i believe? its saturated the exhaust gaskets and came through egr block off. dripping...

edcmat-l1

iTrader: (10)

Cyl. 3 and 5 are on bank one. What are your IAC counts at start up? What are they when the engine is warm and idling? Scan it, check this and report back.

Edit: Just reread your post. If the IAC is zero, that is a sign of a vacuum leak. Same as the cold idle condition, and the fact that you're commanding 600 rpm idle speed, but actually idling at 800 rpm. All points to a vacuum leak.

Dillon93dillon

sorry cylinder 4 and 6.. are puking fuel/oil out. my brother is thinking its stuck injectors possibly.

ive got a live data picture i will post up that shows all the numbers.

edcmat: i sprayed EVERYWHERE, throttle body, intake, brake booster, booster is holding vacuum, didnt hear single hicup or acceleration in idle.

My IAC doesnt make any noise like i heard it should when you shut the engine off, how it should reset to a base idle spot for next fire up.

Frost

iTrader: (45)

It's a closed loop control system (both idle and fuel) not an old school carb'd engine; you sure aren't likely to find the leak by spraying anything.

The advice Ed gave you about IAC counts is valid and should be looked into.

Dillon93dillon

Here is a few pictures of some live data i got.

I also found out today, that my FPR is bad again... which i think the cause it because some reason my walbro 255 is pushing 110 psi fuel pressure.

really puts my at the cause of thinking this is why im having the issue, although the fpr wasnt bad yesterday when it still ran horrible

edcmat-l1

iTrader: (10)

How are you testing the fuel pressure? If you dead head a Wlbro 255, with regulating it, it is capable of 100 psi+.

You don't really have any screen shots with desired idle, actual idle, desired IAC and actual IAC all on one screen. If your desired idle is lower than your actual idle, and your desired IAC is 50 and the actual IAC is 0, then there's only 2 possibilities. IAC is bad, or there's a vacuum leak. Find someone with a smoke machine and smoke it.

Dillon93dillon

usually my idle will bounce from 600-1400, and just drop slowly and rev back up.. numerous times. and will start around 2k rpms even when warm and take about 2 min to work itself down.

My desired idle is always lower than what the truck is actually idling at.

update: replaced the FPR on the fuel rail, and found out it was the sending unit return line not flowing enough, which was building my high pressure but its still got the bank two blowing smoke, way to rich compared to bank 1. but will read 60psi (about 50 steady when idling) and hold it when its shut off for a period of time

maybe got a fould plug also now? or debris in the injector holding it open.

seems to run decent and holds fuel pressue, but smoke

No smoking issues now, had to clean out the pipes.

all of the live data was looking good when i hooked up tech 2 today, 02 sensors were reading correctly everything.

the VSS tho was saying i was moving at 13mph standing still...
from what i remember about wiring is that these speed sensors send out a AC current, which being next to other wires the AC current would alter and change, (pick up other surrounding voltage) so when i moved this VSS wire away from the rest of the wires, it went to 0mph like it should.

not only did i fix that, but by the ecm thinking it was moving was causing my higher idle, when it went to 0mph it instantly went to 600 rpm and held steady.

Steve Bryant

iTrader: (1)

Dillon93dillon,
This is great news! I'm glad that things are looking up for you.

All my best,

Steve

Dillon93dillon

yeah, thanks.

i need to figure out if just electrical tape will cure the interference issue the vss was encountering