Edit: Almost forgot the car is a 93 TA, M6

I hope you guys dont mind me posting here. Most LT1 guys dont know anything about a SD setup. They seem to be infatuated with their MAF's for some reason. So I'm here to beg the great SD guru's for help :hail:

Well here's the problem, my car idles like crap. Its very rough, it feels like I've got a nasty cam in there when its really the stocker.

With the stock programing my BLM's at idle are 108/108 with the integrators dropping down into the mid 80's. It looks like the ECM is trying to pull a ton of fuel. The ECM also goes in and out of closed loop quite a bit which doesnt help matters any. I can tweak the VE tables to get the BLM's up but they still fluctuate quite a bit and the idle still sucks.

The motor is stock internally, stock cam, heads, rockers, etc. The only mods of signifigance are a CAI, longtube headers, and heated O2 sensors (I converted over). The injectors are stock, as is the FPR. I also verified its running the correct fuel pressure (45psi with the vacumn hose off). IMO with such minimal mods I have a hard time beliving the factory programing is that far off.

Here's the interesting part, if I reprogram the chip for PE Idle by setting the TPS to PE threshold to 0% (for just under 1200rpm) the idle is dramatically better. This little hack enables PE mode at idle so the ECM stops making corrections. While it was running like this I borrowed a wideband O2 and it said 13.0:1 while the stock O2s were in the 900mv+ range.

Now since the motor idles much better with more fuel I think the ECM is trying to lean the mixture alot more than it needs to. Unfortunately I cant stop the ECM from doing this unless I go to a open loop program which I am hesitant to try right now.

The big question is why is the ECM trying to pull too much fuel? Only reason I can think of is that its getting faulty readings from the O2 sensors. In other words the sensors are telling it the engine is rich when it really isnt, so it starts taking fuel out unnessecary.

I should really get a wideband on it again while running in normal, closed loop, idle to verify if its really lean or not. But it might be a while before I can do that again so I'm looking for ideas to try in the meantime.

Suggestions? I'm sorta stumped at the moment...

BTW if you're wondering why I just dont leave it in PE idle its because I get some nasty low rpm surging if I try to drive it in that mode.

Any help would be appreciated. This fake cam lope is getting old fast...

Thanks!

 

You say your O2's "were" reading in the .900s when the wideband said 13.0:1, and you have not verified that the new heated O2's read yet. Scan it & see what they are saying, you're totally on the right track; the surging does sound like a lean condition.

I don't even think you need a wideband as much as you need a basic scanner to see what the O2s are saying now. You've already established what the problem was w/ the stock O2's and it doesn't seem that anything has changed w/ the heated O2's. You're just at the "SD isn't happy w/ mods; time to tune" threshhold.

I don't know if lowering FP w/ your AFPR would be beneficial or not, but I'd say it's something to try...

Would your chip mods have caused the O2's to be read incorrectly in the PROM? (please don't take that as an insult, just trying to think outside the box, and it probably doesn't have foundation but...)

Matthew

 

Thanks for the reply. I really appreciate the help. First let me clarify a few things...

The programing is totally stock right now. I had played with it a little to see if raising the BLMs would help the idle. It didnt so I went back to stock.

The heated O2's have been in for quite sometime (about 6mo). All of the readings in the first post were with the heated O2's installed. In other words I was getting 900+mv readings in PE idle with the heated O2's.

I do have a scanner, and a labtop to record some runs so I can tell you anything you want to know. Also the surging only occurs with I try the PE idle trick. With the stock programing (which I am running now) it drives great except for the crappy idle.

Currently the O2's fluctate at idle since the car is in closed loop. The only reason I was able to get steady O2's readings before was because I enabled PE mode at idle. Once I saw the idle get better with more fuel I went back to stock programing to troubleshoot my problem.

I almost think the O2's arent reading correctly but at $32ea I'm a little hesitant to just throw in another pair. Anyone know a way to test them?

Edit: I forgot to mention this but the fuel system is also totally stock. The fuel pressure regulator, the injectors, pump, etc... everything. Fuel pressure is at 45psi which is normal.

Thanks again!
Jason

 

My van originally had a heated O2 sensor in the Y-pipe. Then I put the 350 in and with it came a different ECM (7747 now). It would never idle right. It kinda did what your saying but not that extreme. It would surge up and down repeatedly from a cold start.

Then I switched to a 1-wire O2 sensor (what the 7747 ECM normally was used with) and it ran perfect. I know some guys here just converted right over with no problems but I SWEAR that it was the heated O2 sensor not agreeing with the stock chip. It was trying to enter closed loop too early or something...at the time I didn't have a scanner.

Too make a short story long I'm going back to the heated sensor so I can run a set of longtube headers. The 1-wire O2 won't stay hot enuf with the longtubes. I'm slowly getting the heated O2 tuned in before I switch to the longtubes.

I had to adjust the closed loop timers and hot/cold start temps (thanks to Glenn...) . I set the cold start temp DOWN, and all the timers UP. This way it'll run for a while before going into closed loop. Another funny thing that was in the PROM was a an RPM limit for hot starts. It was set to 1000 rpm. I have my start-up idle set a little high...and I think the two were conflicting somehow...so I set that to 1400 and it's almost right.

Hope this helps

 

Thanks for clarifying a lot of things for me; I was at work and read a little too quickly through your post.

Sounds like AstroCap. is onto something; it's definitely worth trying 1 wires. Personally, I have never been unhappy w/ the reaction of 1 wire O2s on SD or MAF cars when read on my scanner. What reason did you have for running them other than the obvious quicker warm up / closed loop? Is there any meaningful difference once they're all warmed up? I have heard of cold running engines that wouldn't stay in closed loop at idle because of O2s cooling off, but I doubt that's an issue in Orlando or w/ heated O2s I've heard of Delco O2s fixing this problem on cars that had off-brand O2s in them though...

On your scanner; is it reading an average of the O2's or are there 2 readings for them? I wouldn't be a bit hesitant to buy new ones to try. Fixing the idle for $65 would be worth it. Only way I know to test them is to see how they respond on a running car.

PS, what's the stock rear gear in a 93 M6? 3.23? And the 2.95 first / .62 sixth tranny right?

Matthew

 

From everything you have said, your engine IS running too rich. 13:1 (which is rich) can easily relate to .900 volts. Remember that the "stock" (non-wideband) are highly inaccurate outside of 14.7:1. So 900 mV can actually be 13:1 (which is rich).

By any chance do you have relocated MAT?

 

Thanks again everyone.

AstroCap: I dont recall having any problems after switching to the 4 wire, heated O2's. The main reason I switched was because I felt the single wire ones werent getting hot enough with the longtubes.

JMD: I will try to "borrow" a single wire sensor out of my mom's Cavalier to see if the readings change any. I went to the heated O2s beacuse I was getting all kinds of weird BLM readings with the stock sensors after I put the longtube headers in. They are GM/AC Delco sensors FWIW.

The scanner gives me 2 seperate values for the O2's, no averaging.

93 6speed cars had two rear end options, 3.23's with a 2.97 1st or 2.73's with a 3.36 1st gear. The 2.73 cars are very rare, so the vast majority of 93's had 3.23's. My car included...

Glen: I understand that 13.0:1 is rich. But my point was the engine idled actually idled MUCH smoother running that rich. Its only when I run in normaly ( in closed loop) that I have the rough idle problem. Also the MAT is in its stock location (TB elbow), I have not relocated it...

Thanks!