I had previously posted this in tech/perf 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!!!

 

Verify your long tube headers are not leaking. Could be sucking in air.
Hank

 

Hank- No, headers are tight, plus this problem existed before the headers. I would also think sucking in air would cause it to run lean not rich.

 

What cam is in the engine? If its a DRM modified engine with a DRM cam, the only thing that would cause the trims to be skewed like that is if the calibration is off. That is if the rest of the sensors are OK and it seems that they are. One other sensor that can cause a rich condition is the Engine Coolant sensor. If its way off it can cause an excessive rich condition. But from your post it seems that you replaced it already. Also you can and should check the wiring to the ECM, measure continuity between the coolant temp sensor signal wire to the ECM it should be less than 5 ohms, also check all the ECM grounds and engine grounds. Is there anyway the injectors can be leaking causing a rich condition?

 

Yes, it has a DRM cam although I don't have the specs. I have already replaced the CTS once but one thing I noticed is that the temp on my scanner indicates a much higher temp than what my guage shows(50-60 degrees) but the fan kicks in when my scanner shows 205 so I didn't think it was an issue. Now I know the sensor is fragile and who knows if they dropped it at the store or something. It's only $9 maybe I should swap it out again just to be sure. I already have but I will double check the grounds and wires to the ECM.

Not to say that it's impossible that I would have injectors leaking but wouldn't that cause some other symptoms like running rich when in open loop, hard starting, or run on?

 

Yes, leaking injectors would cause a rich problem in open loop as well. It could very well be the chip calibration.

 

Are the chip calibrations going to change over time? The DRM mods were done a few years ago.

 

Does it run rich with a load? or just at idle?

I was concerned with the same exact thing with my 93 auto, and the general concensus from the techies was that at idle does not me jack, its under a load or crusing that matters the most.

However i only had a split block issue and it was only a couple of points.

But i took my scanner out and drove around with it logging, (I have a Xray 3000) and all was withen spec.

Justa thought

 

I think tjwong is on to something here. Have you checked the items he suggested?

Frank

 

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 pressrue 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.

 

128 is the number you want when driving steady state, you want to check each BLM cell.
You'll get some fluctuations in the BLM's/INT's as you push the gas and let off.

 

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?

 

I'm betting it goes away when you replace the ECM. One thing I have learned from twenty years of working with computers and digital switching systems, you cannot trust the diags when the computer itself is insane.

 

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

 

When its running what is the MAP sensor doing? That sensor determines engine load. If it is giving the ECM a false signal the ECM may think that there is more load then there is. A higher MAP voltage equates to less vacuum, less vacuum means more engine load. At WOT you have zero vacuum or high MAP pressure which is about 101 kPA. Check your MAP sensor, and its seal to the intake, if its leaking there the MAP sensor would send a false signal and the ECM would fuel for a high engine load state which would mean it would enrichen the fuel requirements.

 

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

TJ- If I recall my MAP numbers were OK but I will double check that. What would cause the rest of the problems? It was running good in open loop just rich in closed loop before the ECM swap. Now it's being crazy.

 

Is this the sensor on the bottom left of the water pump on the front of the motor?

 

I'd ohm at the injectors cold and hot or after it goes rich, though generally the bad one will be limited to one side and you can pick up what side it is on your scanner. A leaking header would make it lean not rich - or at least the BLM's would be lean; ditto if the air pump circuit was flowing air to the headers. If it's not an injector, check fuel purge - just clamp off whatever line sucks in the fumes to see if whatever controls it isn't sticking open after it's been running for awhile or remove the MAF connector and see if the Intake Plenum smells like gas.

 

Qwiketz- Coolant temp sensor is located in the front of the water pump as you mentioned.

SunCR- Not the fuel injectors and this year doesn't have a MAF.

I'm pretty sure I've figured out what the problem is but didn't want to post until completely sure. With the car throwing no codes and having replaced almost every sensor on the car to include having the injectors cleaned and tested I had to start checking the mechanical side more. Although it wasn't easy to see I found 2 broken valve springs, both intake on opposite sides(1 & 2). Well this would definately account for it running like crap and running rich. New springs should arrive tomorrow and I will post when I have them installed.