pac1085

The Lterm&Sterm values on the left side of the engine get up into the 180+ range, and the car keeps the left side injectors open for alot longer. It never used to do this, but the car was sitting for almost 2 years (we started it multiple times per month but never drove it) This is causing the car to misfire and run really bad. Upon first starting the car, it seems fine for two or three minutes (even if its a hot-start where it goes right into closed loop) but then it goes down hill from there. The car is drivable but breaks up around 3000 rpm, lower if you are going slow in a high gear. Since it runs fine at first I dont see how it could be the plugs or wires, but I'm going to check them when I get home. The car is running a known-good tune.

The right side is fine, both Lterm&Sterm stick at around 128.


In DataMaster, where it lists the fuel trims...two values, one left, one right...which one refers to which side of the engine? Is the left one the "left" side of the engine when sitting in the car and looking forward? Or the "left" side when standing infront of the car looking down at the engine?

car:
95 formula m6
ati p600b @ 12psi
speedpro powerforged pistons (~9.2:1 cr)
eagle h-beams, scat crank
accell 44# injectors, oem fuel pump w/ ATI piggyback
MSD 6AL
random tech catted y-pipe, flowmaster 3"
1 3/4" jet-hot coated headers
ASM 58mm TB
mild comp cams blower cam
etc


Any ideas what to check out?

Thanks!

OBE1 95Z28

Sounds like you have a bad O2 sensor on one side. You can verify by looking at your data master files or swap the O2 sensors from side to side and see if the problem follows the sensor. An exhaust leak at the manifold can also cause this. Bank 1 is the driver's side of the engine; not sure of the Datamster definitions of left and right, should be in their definitions.

Guest47904

Do you still have 2 year old fuel in the car?

Did you put preservative in the fuel that was left in the car when it first purchased?

Wild1

A couple of things could be causing this. The other side could be that the BLMs need to be aligned... 180 is way off.

You may have a stuck injector. Did you put "Stabil" in your fuel before storage? Did you perform a Sea Foam treatment before storage?

If it sits, you may have some hungry mice nibbleling on the spark plug wires. Check the bank that is the concern. Run a strong visual to see that chunks have not be chewed out of the wires... check the coil wire too.

pac1085

thanks guys, I think i mightknow what the problem is now.

i did find a loose spark plug, but i threw a new one in and made sure it was tight and the issue still persisted

I don't know why I didn't think of this earlier but here's what I did..drove the car around so it would get up to temp, then clicked the ignition off and back on so it went into open loop. It runs fine in open loop.

So I'm thinking the O2 sensors. they are the originals from 95 as far as i know.

the MAF is used in open loop, correct?

Injuneer

Everything is used in open loop, except the O2 sensors.

How did you scan it? BLM's can't go over 160, unless you've got a custom tune, and few tuners extend the upper limits. And it doesn't go "right into closed loop" on a hot start... there's still a time out limit.

pac1085

I have DataMaster to scan it. The BLM's actually hit 200 at one point. It is a custom tune by Brian @ PCMforless(until I get some issues taken care of and a proper dyno tune). I know it doesn't go right into closed loop which is why I turned it off/back on, it stays in open loop for like 2 minutes and runs fine until it goes back into closed.

pac1085

sorry I was wrong. the BLM (lterm) gets stuck at 160, the sterm is the one that goes to 200.

looking at the log the left side o2 sensor doesnt go above 178mv or so. I'm going to order two new denso o2's for it and go from there.

Injuneer

I was referring to this statement:

pac1085

ooops, didn't notice i wrote that yesterday. it makes more sense now as to why it was fine for the first few minutes.

thank you for the input, hopefully the o2's will do the trick.

1badasZ

where can you get the densos at i need some new o2's myself

pac1085

you can get the denso's at sparkplugs.com 234-4012 is the part number, $36 each.

I ended up putting Bosch in since I was able to get them today locally for $52. It seems like people here prefer the oem ac delco's but ive had alot of luck with bosch/denso on other apps. It fixed the problem and the car rips now.

Ran into an issue...when I removed the old o2 sensor half of the threads were ruined on the bung since apparently it wasn't stainless and is old (ASM 1 3/4" jet-hot coated headers ~10 yrs old) so the threads in the bung + old o2 sensor kinda welded themselves together. I managed to get the o2 sensor in , will have to get the headers repaired or replaced eventually but it works for now. I was going to replace the passenger side o2 sensor as well but it looks like the starter(i think) needs to be removed in order to get it out.