I had previously posted this here before but still struggling with it. I have a 93 LT-1 6sp (45,000 miles) that is running pig rich in closed loop. No problems starting at all and runs really smooth in open loop. I have an autoxray 5000 scanner and when it goes into closed loop I can see the O2's start bouncing back and forth in a good range. Once I bump the throttle a few times it will start running really rich. These are my scanner readings once it is running rich:

coolant temp: 205
Map sensor : 2.46
Throttle sen : .54
Left O2 : 900's
Right O2 : 900's
Left block learn: 108
Right block learn: 108
Block learn cell: 16
Left Integrator: 64
Right Integrator: 64
Idle air meter: 17 steps
Spark advance: 22 degrees
Knock retard: 0 degrees

Now for the components I have replaced over the last month:

TPS, IAC, MAP, CTS, O2's (Twice Bosch and then Densos), Fuel filter, Spark plugs, new Em longtube headers with RT cats. Opti was replaced less than 2000 miles ago.

The first symptoms was a stumble once it went into closed loop. When I would stop at a light it felt like it wanted to die but never would but it felt like it was running on 6 cyls. I never once have gotten a code. I havn't been just throwing parts at it in hopes of fixing the problem even though with the laundry list above it would appear that I am. I do have a helms manual and have been reading it religously but like I said no codes. The MAP replacement seems to have fixed the stumble but the richness is definately still there.

Now the engine is a DRM modded 383, DRM prom, adj. fuel reg. last checked it read around 41-42.

The car has run great for a long time no problems no codes. It all started with the stumble. What else could be causing the car to run rich only after it goes closed loop? If it was something in the fuel system (injectors etc.)wouldn't it run rich in open loop as well? Ignition coil getting hot? I disconnected inlet temp sensor, no change. Removed and cleaned TB.

HELP!!!

 

Well if it runs good in open loop you can eliminate: injectors, pump 7 filter.
For closed loop it is all up to the MAP sensor, O2's, TPS, CTS & ECM.
Does the Opti use an ignition module? If so that is a possible cause too.
Beg, borrow an ECM to try it may be going on the fritz.

 

With those BLM #'s the ECM is not in control. You have done about all there is to do....except replace the ECM. The prom is probably ok as there isn't a code thrown and it runs well in open loop. Just for fun tho, I would check the main grounds, especially for the ECM.

 

Agree about the ECM as a possbile culprit, but also note that I replaced my Ignition Control Module (ICM) two weeks ago and picked up 2 mpg. I had been averaging 16.5 - 17 mpg around town, after new battery and new Ignition Control Module I'm now averaging 19 - 19.4, and she runs more consistent.

If you are running or have ran any aftermarket ignition coils, they can be hard on the Ignition Control Module.

*I'm not saying it is the ICM* but as an electronic part it could be functioning correctly at low temperature (open loop-- engine is not very hot yet), it then begins getting hot from its own operation plus the heat from the passenger side cylinder head to which it is firmly mounted, it may start falling on its face.

 

Thanks guys- I'm thinking ECM myself, I'm just trying to eliminate anything else before replacing it since I don't really see a way to test it without "replacing it with a known good ECM". I may try the ICM but it seems like a faulty ICM would give me more of an intermittent problem than a super rich condition every time. If anyone can think of anything I may have missed please chime in.

 

Actually it looks like the ECM is trying to lean it out when it goes rich. Those low BLM values say that the ECM knows about the rich condition but it is our of it's adjustment range.

Look at the MAP values when it is running well in closed loop (i.e. BLMs are ok) and then after it goes way rich and check the injector pulse width under both conditions. This will tell you if the ECM is doing it's proper job.

Could you have a problem with the injectors or FPR. You might monitor fuel pressure under normal & rich conditions.

Put your scanner into Monitor mode and do a WOT burst from a stop into 2nd gear. Then take a look at the O2 sensor values. If they are in the 890-920mV range fuel delivery is ok at WOT.

Also, when you are collecting scanner data before & after running rich, take the data above idle, say at a steady 1,500 or 2,000rpm. Use the Monitor mode to capture data over time instead of the Scan snap-shot. This may give you a better picture of what's going on.

 

I just went and bought a fuel pressure guage so I will try that tomorrow with the scanner. I also bought an ignition control module so I'll see if that helps at all.

 

Well I went out this morning and checked fuel injectors, they are not leaking. I went on a test run with the fuel pressure gauge and scanner hooked up to check my system under load. The car ran great the whole time, never stumbled once at any RPM. Once I got the RPM's up the O2's never gave me another problem, they bounced back and forth as advertised even when I stopped and was at idle. My fuel pressure was a little low about 38 so I bumped it up a few lbs.

Now here is the question, my short and long term fuel trim bounced around quite a bit at all loads and RPMs but I would say they averaged 128. Is 128 just the perfect reading when A/F ratio is 14.7 to 1? Is it supposed to stay at 128 or is the bouncing back and forth normal and it's just the ECM and sensors adjusting to the 128 standard? Of course I've only had my scanner on my car and I just got it a couple of months ago. I'm getting closer and it sure was nice to have her on the road and running good again.

 

I'm pretty sure that the 128 blms means that the ecm isn't correcting the fuel trim at all which would mean your tune is about as close as it could be as far as the fueling goes. Glad to see it wasn't anything major, just one of those things that has to come up every once and awhile to mess with you and keep you on your toes. Now if I can just get mine on the road.

KC-Shadetree Performance

 

Reference your last post, is that after you installed the new Ignition Control Module? If so, maybe it fixed your problem

P.S. You want the long term fuel trim to be 128 both sides. That is the goal. Short term will fluctuate above and below 128, but should stay within several clicks of 128 either way if everything is in tune.

 

Yes, that was after I replaced the ICM. -Thanks Lone Ranger- I think it helped a bit but I don't think I'm quite 100% yet. I need to drive it some more and try to get that fuel trim straight.

 

the BLM is the long term fuel trim. The intergrators are the short term fuel trims. If the intergrator lives mainly above or below 128, the BLM's will change adding or subtracting fuel and retain that. There is (as I recall) 16 BLM cells + 1 for idle). The blm's should stay more or less constant while the intergrator responds to the O2's. If your BLM's are at 128, that is about is good as your going to get. The short term intergrators will swing as like your O2's. As you accelarate, the ECM goes thorugh each cell depending on the speed/ RPM and adjust PW according to the stored BLM. Hope that makes sense.

 

If it was the old ICM as part of the problem, it will take some driving time for the ECM to adjust/learn-in the fuel trims now that the engine is getting better ignition. So they may stabilize on their own after more driving, if that was the case.

 

Well I took it out for another test drive last night and she ran great. I still had the split BLM's but it ran great. I thought I had her about fixed.

I went to drive it into work today with the scanner on and I got just up the road when she goes into closed loop and BAM she falls flat on her face again. O2's running rich 800-900 and up, short term fuel trim at 64 long term 108 and she was stumbling again like it was running on 6 cylinders. What the heck is going on? I drove it up the road a few more miles trying to figure it out but the farther I drove the worse it got. I stalled at a couple of lights but it started right back up. I limped it back home and here I sit confused. How could it run so smooth yesterday on 2 seperate runs and flip on me over night? Not 1 code. How can it run so rich and so poor but has yet to ever flip one stinkin code. My Helms book says that if the O2's stay high for too long it will set a rich O2 code.

What besides a bad ECM and the parts I already replaced could cause it to run so rich in closed loop? Like I had said before it runs great in open loop so I would think I could rule out most of the fuel system components. Am I missing something? No codes, nada!

Well the only good news I have is the price on the ECM. The local aftermarket shop here (Checkers) wanted a little over $300 but didn't have any in stock. I called the dealer just for laughs and they told me for some reason there price had just dropped from $350 to $170, he couldn't tell me why and I wasn't asking. Should be here in 2 days.

Anybody have any thoughts?

 

Seems like it has to be the ECM, after all that has been done so far. Can't think of anything else. And that is a great price on an ECM.

 

Well my troubles continue, I got the new ECM swapped the prom went to fire it up and it will crank but doesn't want to stay running. If I hold the throttle down I can get it to start but it doesn't want to stay running. My first thought is that they ordered me the wrong ECM so I put my old ECM back in because it always started and ran great in open loop with the old one. Well it runs the same way with the old or new ECM. I seem to be de-gressing here. trying to fix a rich problem and now I can't even get it to run.

I thought maybe it was a fuel issue after all. I had the fuel pressure gauge hooked up and it wasn't holding quite like it should with just the key turned on. I ordered a new Holley AFPR and while I was waiting on it I sent my fuel injectors away and had them cleaned and flow tested by Witchhunter in WA. There was no real problems with the injectors although they did benefit from the cleaning and rebuild. Installed the AFPR and injectors this morning. Fuel pressure is great and holding but the car still has the same symptoms. It will start with some coaxing but it doesn't like it. It runs like crap, very rich and it feels like it's running on 5-6 cyls.

Now this really seems crazy to me but I had my scanner hooked up when I finally got it to start. It seems like it went straight into closed loop. Now it did take me a minute of coaxing her to life before I could even look at the scanner but as soon as I did it was in closed loop (to fast)
O2's in the 900's
L & R block learn 108
L & R Int 64
and both of my fans are acting crazy. Both coming on at the same time and to early. Then #1 stays on and #2 will shut off for just a few seconds and kick right back on and this was when it was only at 160-180.

Totally pig rich still. Oh yeah, while I was waiting on my fuel parts I went ahead and replaced my CTS again just because I know they can be the culprit sometimes. I had already installed a new one but for $8 it was worth another shot.

What would cause it to go straight into closed loop and run like this. I checked the ECM grounds and all of the fuses. Is this going to be a wire gremlin or perhaps is my PROM fried? The PROM was originally done at DRM when they did all of the other mods(years ago). The only mods I have made since DRM is the exhaust (Headers, cats). I was very careful when I swapped the PROM into the new ECM to avoid any static charge or anything but could the new ECM have zapped my PROM? HELP!

 

Coolant temp sensor will force a closed loop if it tells the ECM that it is already up to operating temp.

 

Morley- I replaced the CTS and it is sending the right temp and signal to the ECM.

 

Start it up when its cold. Then move the wire harness(s) that come from the CTS, MAP, TPS. Also trying moving the connectors to each. I wonder if there isn't a intermittent bad wire or connector that is fooling the ECM. Failling that, it almost has to be in the ECM...you've done all the rest.