I've been messing with my car the last month trying to diagnose a miss, and a rich condition. After tearing apart the whole top end, checking the injectors, and checking all the spark plugs, wires, cap/rotor, and oil change, I'm still fighting a too-rich condition.

I have a wide-band O2 sensor hooked into the passenger side, and a 3-wire heated O2 on the driver's side for the ECM. The wide-band shows 14.0:1 or so at open loop, but 12.7-13.1 during closed loop. I've checked the wide-band on both sides of the engine, and its the same. I have 30lbs injectors at 46 PSI, and the ECM is set at 32lbs. I have my Ostrich set up, and Datamaster to log. The Datamaster shows the BLM and Integrator around 125-130, but the wide-band still says 12.7:1. I have adjusted the injector constant from 30lbs all the way up to 50lbs, which should not even allow the car to run, yet it still sit not higher than 13.5:1. I adjusted the VE tables too, and still no luck. I have tried a different ECM, and a different PROM chip, with no luck. I checked the fuel-pressure regulator, and it does not appear to be leaking. We checked the headers with a temp gun, and they're all around 350*.

I'm at a total loss now, as it wont pass emissions with the fuel too rich.

We've even put the wideband on Don's car and it reads normally, about 15.0:1 at idle and 14.6-15.3:1 at part throttle.

Anyone else have an issue like this?

 

Kevin,

Just some thoughts off the top of my head...

Have you run through the standard voltage checks at the back of the ECM? Make sure the ECM is seeing all the correct inputs.

http://chevythunder.com/fuel%20injec...ecm#1227730%29

I assume you've looked at all your sensor readings and they look correct.

How's your O2 sensor ground? On mine, I discovered there was enough electrical resistance between main ECM ground and the O2 sensor bung at the header collector that I ran a braided ground strap from the O2 sensor body directly to the back of the cylinder head. Definitely don't want ground loops on the sensor that the ECM depends on for knowing how to adjust fueling.

Is the 14:1 at open loop what you expect for your calibration? If not, what was it before?

Is the "richness" the same at all operating conditions?

What happens if you disconnect the alternator plug? Wild thought... but maybe there's electrical noise in the system that could be causing problems.

Maybe output a .csv file from Datamaster and send to me. I can take a quick look at it.

ultm8z@yahoo.com

 

Kevin, Did you check to see if the injectors are leaking?

 

Sorry for not being more specific when I said I "checked the injectors." Yes leaky injectors was the first thing I suspected too, but when we had the top end apart, we put the injectors into our flow bench, and they all measured 16 ohms, and they held 50 PSI of pressure just fine, and they all sprayed normally when grounded.

No we didnt check the ECM grounds, but the wire harness has never been changed, its still factory. I don't think its an O2 problem as we tried regular O2's on both sides when we switched the wide-band O2 from one side to the other. Changing the injector constant and not getting any results is the weirdest issue to me.

I dont have the data log here but I can attach the bin file. The forum software made me zip it first, it wont accept bins.

 

I have read that higher psi injectors are quite troublesome at lower RPMs. They just can't control fuel well. If I recall correctly this is mainly at lower RPMs only.

 

Is the problem just at idle or everywhere?

Understood its the factory harness, but it's getting on almost 25 years old now... It wouldn't hurt to back probe the ECM connectors to that link I posted and verify the ECM is getting all the inputs it needs.

 

Would reprogramming EPROM fix this?

 

Yes its everywhere. From idle to 3000 RPMs the air/fuel ratio on the wideband O2 shows 12.5 to 13.5:1 no matter what I do with the injector constant. We'll have to check out the grounds and the ECM connections.

 

Changed all 8 spark plugs yesterday with brand new ones. Some looked dark like they were running rich. Now the car runs about 13.8 - 14.3 in open loop, but still drops to 12.8 to 13.3 when in closed loop. However, changing the injector constant now has a noticeable affect. Normal IC is about 33lbs, I can see the BLM get higher towards 160 as I raise the constant, and the car starts running rougher. Surprisingly though, the air/fuel on the meter still doesnt change that much. So I tried locking out the BLM and INT to 128 and then raising the injector constant. That did help, but again the car got too lean and was idling rough. Air/fuel was bouncing between 14.0 to 15.0 and up. It never held steady, like I would expect. I checked all the spark plug wires again, and they seem fine. Next I'm going to remove the plenum again and open up the fuel pressure regulator and check for tears in the diaphragm. I keep thinking this is fuel related.

 

I still say see if you can get me a data log (.csv export)... maybe another set of eyes on the data may help yield some clues.

 

Coolant temp sensor? Possible coolant sensor is suggesting cool coolant when in fact it is not... However that would affect the OL as well. Vac leak? That would affect the BLM driving it up and add gas in CL.

 

I'm curious to see the results of the DMM check on the ECM pinouts, and a datalog if possible. Need to see what information is being received by the ECM.

I kind of agree with Ronny's line of thinking that the ECM is getting "fooled" into adding more fuel. It doesn't sound like a fuel delivery issue from a "mechanical problem" point of view.

 

There are two coolant sensors. One for gauge on dash and one for ECU. Do the datalogs show correct or realistic coolant temps? If so like not the sensor...

 

Can you adjust closed loop o2 sensor constants?

 

Attached to this post is the Datamaster Autolog file. Remove the .txt at the end so Datamaster will read it.

I held the throttle at idle, 2000 rpms and 3000 rpms to give an idea of whats happening. We didnt get a chance to mess with it today.

It still "pops" out the exhaust like it has a misfire, but all the header temps are similar. We hooked direct battery voltage to the coil to eliminate the wiring, with no effect. Next we'll try changing out the distributor.

 

Kevin, possible to convert to a .csv file? Or something I can import into Excel? I don't have datamaster.

 

Kevin,

I downloaded Datamaster and started looking at your log file (posted above).

I notice you're stuck in cell 4 even when not idling. Has that been typical before the problem developed?

Also, the bin you posted, I assume at one point the car was running properly with it? Just curious about baseline...

Also, your IA temperature is saying ~85F (24C) on the datalog. Is that reasonable for the conditions you were in during the run for this log file? Where is your IAT mounted? Do you remember what the ambient temperature was approximately?

Lastly what's the significance one a cell goes pink or light blue on the datalog replay?

 

I dont know on the cell 4 thing, I've never looked at that before.

Yes the car runs awesome right now after a tune-up, but its still slightly rich at 25 MPH based on the smog numbers.

My IAT is relocated to the front air intake, and I made the modifications in the bin file for that mod that were posted here previously. I thought about putting it back under the plenum and seeing if that made a difference. Last two weeks it was about 70-75* degrees here.

Pink or red means its rich, blue (its green on my display) means its lean.

 

Being stuck in block 4 will cause a rich condition. Does the ECM show a vss signal ? Any changes in the tune to eliminate ccp ?

 

Just an update, as I finally got the car to pass the emissions test after putting two new cats on it. We found one of the cats was half-missing its substrate. Now the emissions numbers were way down close to zero as expected.

By the way, yes the ECM sees the VSS signal and no I have not removed the CCP. The only sensor changed is the IAT relocated to the airbox instead of under the plenum, but I changed its code to compensate for that.

 

I think the factory cal will force you into BLM cell 4 until the CCP reaches 21% duty cycle.