PontiacBonnevilleClub.com

Alright I had two or three threads going with multiple information. I'm going to end those and start this one.

Issue:
Car has a hard time idling without the IAC cranking itself up. When warmed up, IAC ranges from 10-25 to keep it running. Occasionally (like 50% of the time), it surges and misfiles pretty badly when you hit WOT from dead stop and no other time. It's hitting between 4-6 psi of boost at 750 ft elevation, Fuel pressure hangs around 32-35 PSI with foot off throttle cruising around, and when you WOT the throttle it spikes up to around 47 PSI. Key on engine off it surges to 42 with pump running and stabilizes at 38 once pump shuts off. At idle, I'm seeing 35 psi.

Video of fuel pressure and symptoms:


I replaced the LIM, Supercharger and TB gaskets a few weeks ago with no change other than lower operating temp (around 180 if moving, still 200-210 if sitting for a while). Fans kick on as needed. Today I replaced the PCM, and it fixed my traction control and stopped throwing a P1650 QDM#2 Circuit Fault. I still get a fuel trim sensor lean code, and that's it. But what determines if it's running lean or not?

Today I did a few WOT runs with scanner and really wasn't sure what the expected values for. At WOT, LT Fuel Trim was 128 and LT Fuel Tr Cl was 10, KS Counter kept going to 255 and back to zero whenever launching hard (which I know is bad). MAF was at 4-6 gr/sec at idle, and typically hung around 148 at WOT. I think I saw MAF surge to 204 once at WOT though. It was cleaned when I got the car with CRC MAF cleaner. I've tried spraying vac lines w/ carb cleaner and it didn't reveal and leaks. Valve cover gaskets may be leaking a little, would that could hesitation due to lack of crank pressure?

What do you folks want me to read during WOT/Idle to try and determine the root of this problem? I am planing on getting a set of FSMs from the owner (RedRocket) as soon as possible, just waiting for things to go right for both of us.

Replaced:
PCM
LIM Gaskets
Supercharger Gasket
TB Gasket
Spark Plugs
PCV
Fuel Filter
Thermostat
Coolant
Oil & Filter
Air Filter
All straight vacuum couplers

I have a funny feeling I missed a lot of things that I replaced. I'll post them as I remember.

Get LTFT, STFT & MAF. Can you get the MAF frequency instead of GR/sec?

Both fuel trims should be around 128. IIRC the range is 0-255 with higher numbers being rich.
You get the P0171 code when the trims are rich due to the PCM trying to correct the lean condition.

My theory is if the trims are rich at idle & get leaner as rpm's increase then it may be a vacuum leak.
If the trims are near 128 at idle and get richer as rpm's inrease then it may be a fuel delivery problem.
Just a theory at this point.

Try to limit WOT until you get this resolved.

that's a lot of knock counts O.o

i agree, stay out of the throttle

Mike, do you want those numbers at idle or throttle? I've only been doing WOT for scan purposes.

We need both to make a comparison & you can do both while in park. Just getting the RPMs up to 2,000 should be enough to see which way the fuel trims are going.

Okie doke, tommorrow night should be the first time I'll be able to do it. Thanks.

Alright, here are the scan results.

Coolant temp was around 200-205*, even w/ 180* t-stat and fans running.

A new code appeared, 131. Said low O2 voltage. Battery was always between 13 and 13.4

Idle
Lt. Fuel Trim 160, and the Tr Cl ranged from 0-16
St. Fuel Trim 182
MAF read 4 GR/Sec (That was only reading available for MAF)
Injector Pulse Width 0
18* Spark Advance
O2 read 13-22 mv
IAC was actually zero for a little bit

1500 RPM
Lt. Fuel Trim 160, Tr Cl 1
St. Fuel Trim 168-175
MAF 7 GR/sec
Injector Pulse Width 0
19* Spark Advance
O2 read 80-850 mv???

3000 RPM
Lt. Fuel trim 157, Tr Cl 5
St. 120-130
MAF 15 GR/Sec
Inj Pulse Width 0
23* Spark Advance
O2 did same reading 80-850??

So why does my O2 do that? O2 wouldn't affect how it's running in open loop, no? Traction control randomly wouldn't turn back on again. Restart fixed that.

Looks like a vacuum leak to me. Did you repeat your soapy water test after changing the gaskets?

Try disconnecting & plugging some of these vacuum lines.
Large line at the brake booster.
Lines going to the evap canister.
Lines under the supercharger.

Does the idle change when the cap is removed from the valve cover?

The vacuum tree on the supercharger, it seems a bit loose, but it won't come out. Could it be leaking?

spray some carb or brake cleaner on it, see if the idle changes

Alrite - what exactly do you mean by the lines under the super charger? Just the lines that control the bc or what?

Yeah, you can pull both sides off the T & then plug them or connect both sides with a single piece of tubing. IIRC one side goes to the MAP sensor & the other to the fuel pressure regulator. I was mostly wanting to see if the MAP side was leaking. Just plug it long enough to see if the idle improves.

I'm going to guess an EGR tube that's cracked in half at the EGR valve will cause this problem too? Because I just found that...

Called 9 Auto parts places around here including dealer, salvage, and autozone/advanced and turned up with nothing. Any ideas where to get one of these suckers?

Glad you found the leak.

I seem to recall a post stating that these are no longer available. Junkyard or repairing the one you have might be your only choice.
Hopefully someone else will chime in.

I tried some QuickSteel just to see what it does... idled PERFECTLY. I don't think it was 100% sealed as it would hesitate once in a while while driving, but I stopped getting the lean code and it seems like 100% happier. This makes me happy . Thank a lot eh

Oh yeah, one last thing...

I took it for about a ten mile trip, KS counter hit 1, and it sputtered a little bit, but do you think that's because even at idle, o2 mv goes from 20mv to 850mv up and down the scale? . I tried moving it away from wires but that didn't help. IAC typically hangs around 20. I'm also probably going to have to change plugs after running lean for so long.

my 02s do that at idle also, i think its pretty normal.

Your O2 mV should be going up and down like crazy, like you noticed. The O2 sensor is constantly sensing and reporting changes and that's constantly changing the fuel map to optimize the air/fuel ratio. An active O2 sensor is good. When your O2 sensor starts slowing down, getting lazy, that's bad and means you should replace it.
Keith
1994 SSEi

Alrite, thx.

Still hesitates under heavy throttle... and idles perfectly. This is confusing. Can I take the fuel rail and injectors out, have someone turn it over, and I look at the injectors to see if they're restricted?