1992 LT1 Coupe: First time with scan tool

[screamin_conure]

Well, I couldn't take it any longer and I HAD to see my baby!

So, I pulled the cover off, unhooked the Battery Tender, hit the key and she fired right up! I received an AutoXray EZ-Scan 3000 for Christmas, so after letting it come up to about 150 degrees coolant temp, I shut it off, hooked up the scanner and started it back up. First off, the car has a very uneven idle. "Bouncy" is about the best way to describe it. Not very smooth. It's a little smoother in park vs. gear, but not much. It also has a very rich-smelling exhaust, and LOTS of steam-like vapor from the exhaust.

Here's what the scanner told me (I'm posting only the pertinent stuff):

A full trouble code scan returned "No trouble codes found".

Left Block Learn: right around 128, but would fluctuate a bit.
Right Block Learn: 160 (I know, not good)
Block Learn Cell: 16
Left Integrator: Fluctuated quite a bit, but in the neighborhood of 128
Right Integrator: 135 average. Consistantly higher than the left.
Spark Advance: 22 degrees
Loop Status: Closed (went into closed loop after a few minutes of idling)
Both 02 sensors were right in the 570-580 mV range, which I belive is about normal. However, there were times when there was quite a difference between the left and right.

I'm thinking either a bad injector in the right bank, or a flaky 02 sensor. But most likely injector(s). I do have a digital volt-ohm meter, but it's just too darned cold to stand out in the garage and take resistance readings on my injectors! I also got a fuel pressure gauge for Christmas too (boy, Santa really knows his stuff), but again, using it ould have required me to get out of the nice warm interior! As soon as the weather warms up (come on Spring!), I'll be checking these things out too.

So, would a bad injector cause a rich condition and rough idle like this?

 

[vetteoz]

Both 02 sensors were right in the 570-580 mV range, which I belive is about normal.

O2 readings in closed loop should not be static.
Should flip- flop back and forth from hi to lo mV readings

 

[Hib Halverson]

If the right BLM is 160, the system is way lean and adding fuel to the right bank. Look for a fouled injector, a vacuum leak or anything which would cause a lean condition.

Is this engine missing at all?

if you don't have a factory service manual, now's the time to buy one. You'll find a pleathora of troubleshooting info.

 

[screamin_conure]

If the right BLM is 160, the system is way lean and adding fuel to the right bank. Look for a fouled injector, a vacuum leak or anything which would cause a lean condition.

Is this engine missing at all?

if you don't have a factory service manual, now's the time to buy one. You'll find a pleathora of troubleshooting info.

Thanks for the reply Hib. You actually made things a little clearer for me. In looking at the 160 BLM, I was taking that as the computer reporting what the A/F mixture IS (rich), instead of the computer trying to correct a lean situation.

I got the car at the end of last summer, and it spent a couple of weeks with my mechanic to address a number of other issues, one of them being a high idle. He ran a smoke test at that time to look for vacuum leaks and he reported that he couldn't find anything. We ended up replacing the IAC and cleaning the TB at that point, which corrected the high idle for the most part. After the IAC was replaced, he subsequently installed new intake gaskets, which means that a vacuum leak could still be a possibility.

However, if it were to be a vacuum leak, wouldn't I be seeing more consistently high BLMs on both banks, rather than just the right? The thing is, once under way and off of idle, the car runs well. There are no misses, hesitations, bobbles, etc. Even cruising at 60 mph, it's nice and smooth. It's just at idle that it seems to be a vibrating, stinky mess.

I do have a set of FSMs for my year, and while I can absorb technical stuff pretty well, I tend to get lost in those things.

It's supposed to be near 40 this coming weekend, so maybe I'll be able to get out and put a VOM on my injectors and check fuel pressure and hook up a vacuum gauge as well.

 

[92BlackVette]

I didn't even know they had a scanner for OBDI computers wow. What information does it offer when you attempt a scan?

 

[screamin_conure]

I didn't even know they had a scanner for OBDI computers wow. What information does it offer when you attempt a scan?

Yeah, the EZ-Scan 3000 is an older, discontinued model from the OBDI days. I actually found one, brand new, on Amazon.com for $80.00!

I believe that it picked up about 35 different data points when using it in "operational data" mode (live scan). All kinds of stuff: BLMs, TPS voltage, desired idle speed, actual idle speed, battery voltage, O2 sensor voltage, MAP sensor voltage, spark advance, intake air temp, coolant temp, etc. Lots of stuff. Nice little scanner. I've contacted AutoXray and all I need is a software upgrade ($100.00) and an OBDII cable ($50.00) and I can use it on my 2001 Honda CR-V and 2000 Toyota Corolla too!

Looks like there's one more available for $99.00!! Amazon.com: AutoXray EZ-Scan 3000: Automotive

 

[gmjunkie]

If the right BLM is 160, the system is way lean and adding fuel to the right bank. Look for a fouled injector, a vacuum leak or anything which would cause a lean condition.

Double check all vacuum lines,fittings,power brake booster and EGR!!
I'd probly even re-check the torque on the intake!!

 

[vetteboy86]

O2 readings in closed loop should not be static.
Should flip- flop back and forth from hi to lo mV readings

The O2 sensor volts should transition consistently from approximately 50 mV to approximately 900 mV. I don't know the actual numbers. My scanning software records these as O2 counts. The O2 counts will then cycle from 0-255. As vetteoz explains this is in closed loop.

 

[vetteoz]

I didn't even know they had a scanner for OBDI computers wow. What information does it offer when you attempt a scan?

$60 for a ALDL -USB cable and some free software lets you monitor / record all the ECM signals on your laptop in real time.
If you record ( datalog ) then you can replay later at a slower than real time speed to identify problems

 

[Hib Halverson]

What "free software" can you get that works as a software-based scan tester which supports 81-95 GM OBD systems?

Also, what is the source of this 60-dollar "ALDL-USB" cable?

 

[vetteoz]

What "free software" can you get that works as a software-based scan tester which supports 81-95 GM OBD systems?

TunerPro is the most popular
TunerPro and TunerPro RT - Professional Automobile Tuning Software
Datamaster that I show the screenshot above from is free for the 1st 20 logs then you have to buy it.
Only put that up to display typical features because it has the most user friendly interface

What is the source of this 60-dollar "ALDL-USB" cable?

ALDL OBD1 OBD cable OBDI OBD2 engine codes
There are others exactly the same but this is the cheapest I have come across.

 

[screamin_conure]

I've been thinking about the vacuum leak issue a bit, and I was wondering something:

If I were to hook a vacuum gauge to my intake manifold, would a steady reading of about 17" or more of vacuum pretty much tell me if I have a vacuum leak somewhere? Obviously, it won't necessarily tell me WHERE the leak is, just that I have one. Am I barking up the right tree here?

Also, to test general manifold vacuum, where's the best place to attach the gauge?

Thanks again for all of the advice!

Ron

 

[screamin_conure]

The weather here in the Chicago area cooperated enough for me to get out in the garage and do some further diagnostic work. Even got to take her out for a spin!

Here's what I did:

Fuel pressure check: I hooked up a FP gauge to the schrader valve and upon turning the key (no engine start), the needle briefly went to 50 while the pump ran for a few seconds and then settled back down to 45. Shut the key off and pressure stayed right at 45 psi. I left it there while I did the cold injector readings, and pressure dropped to around 40 by the time I was done. Started the engine and pressure stayed right at about 42-43 psi. I think I'm good there.

Vacuum gauge: I teed a vacuum gauge to the port that feeds the EGR solenoid/ASR line, underneath the driver's side fuel rail cover. Started the engine and vacuum jumped to 15" Hg. Revved the engine a couple of times and vacuum dropped to 0, shot up to about 20, and then settled back down to about 17" Hg. The needle was rock solid stable at idle. I think I'm good there too.

Injector resistance check: I checked all eight injectors with a digital VOM, both cold and hot. The results...

COLD
Cyl. # Ohms
2 12.8
4 13.1
6 13.0
8 12.6

1 12.7
3 12.7
5 12.6
7 12.7

HOT - after a 20+ minute drive where coolant temp hit a maximum of about 225 degrees.
Cyl. # Ohms
2 13.3
4 13.1
6 13.1
8 13.3

1 12.9
3 12.9
5 13.2
7 13.3

The injectors are all within an ohm of each other, but I'm not sure about the overall resistance readings. They seem rather low, as I was under the impression that they should all be at least 14 or so. These are the original Multecs, and while the idea of a new set of Bosch IIIs from FIC is tempting, it would be a $180.00 gamble that may or may not correct the issue.

Road test: As I mentioned, I took her out in around-town traffic for about 20+ minutes with the scan tool hooked up and monitoring live data. With a cold start, right BLM shot up to 160 and stayed there. Left BLM was right around 130, give or take. Let it idle until coolant temp made it to 145 degrees and then I set out on the road. Upon getting in motion and the system going into closed loop, right BLM started to come back down and by the end of the ride, was fluctuating qute a bit and actually went as low as 93 while idling at one traffic light. Left BLM was much more consistantly closer to 128 throughout the ride. Both integrators were closer to 128 throughout the ride, but the right integrator did a lot more fluctuating than the left. At no point that I was able to see, did the EGR duty cycle move off of 0%. I thought that was kinda' strange. Once fully warmed up and idling at a stop light, IAC motor steps were at 0, but at a few stop lights late in the ride, the IAC seemed a bit "lazy" and was opened a few steps causing an idle of about 800 rpm while stopped and in gear, and it would then slowly drop back to zero and the idle would gradually come back down. 02 sensor readings were all over the place (from 200 mV up to 800+ mV), but the right sensor seemed to be the most erratic and had the widest and most frequent swings.

So, I'm not sure what to think at this point. Could it be questionable injectors that aren't accurately doing what the ECM is telling them to do? Could it be a flaky 02 sensor on the right that's sending the ECM whacked out info? Whatever it is seems to be centered around the right bank in particular, as the left's numbers seem much more in line. I guess it could be an exhaust leak in the right manifold, either before or at the 02 sensor, causing a false lean reading and forcing the 02 sensor to tell the ECM to add fuel.

Even though I have no trouble codes showing, I'm treating this as a Code 64 (Right 02 sensor - lean exhaust indicated). I still need to try disconnecting the MAP sensor to see if the false lean goes away, and also try pinching the AIR hoses going to the exhaust ports to see if that changes the BLM. After that, it's testing for an exhaust leak, which I have no clue how to do, but I'm sure I'll figure out something.

Either way, I'm getting close to figuring it out. This is fun!!!

Thoughts and critiques are welcomed.

 

[G Winter]

The injector ohm readings are within the allowable specs in the FSM but I would be a little suspicious of the reliability of the injectors.

Glenn

 

[screamin_conure]

Hey Glenn, thanks for the reply!

I'm kinda' thinking along the same lines. Even though they "appear" to be in good shape, I've been doing a bit of researching/reading, and from I gather the Multecs can still be problematic despite good test results. I guess it's better to replace them and know that I'm working with a known good set of injectors before I start using my wallet as a shotgun and blindly replacing other parts.

Per chance, what volume/page number did you find the resistance specs in the FSM? I've been searching through mine, and can't seem to find that.

Thanks again!

Ron

 

[gmjunkie]

Either way, I'm getting close to figuring it out. This is fun!!!

Ya Think??:L:L:L
Maybe not before it's all over!!
Out of curiosity,What is the Learned IAC??

 

[screamin_conure]

Ya Think??:L:L:L
Maybe not before it's all over!!
Out of curiosity,What is the Learned IAC??

Oh boy, I'm hoping it doesn't get to be TOO much fun!!

According to the '92 FSM, learned IAC is: An internal ECM parameter. Each time the vehicle is driven, the IAC system learns how many counts is required to produce a given desired idle.

Sounds pretty much like the "history" of your IAC movement, as stored by the ECM.

 

[gmjunkie]

Oh boy, I'm hoping it doesn't get to be TOO much fun!!

According to the '92 FSM, learned IAC is: An internal ECM parameter. Each time the vehicle is driven, the IAC system learns how many counts is required to produce a given desired idle.

Sounds pretty much like the "history" of your IAC movement, as stored by the ECM.

Yeah That,I want to know what yours is,warmed up good and idleing!!

 

[screamin_conure]

Yeah That,I want to know what yours is,warmed up good and idleing!!

DOY!! :duh And here I was thinking I was being a helpful guy on the forum!

To be honest, I didn't jot down the learned IAC value.

I had it out again this afternoon, and at this point I'm about 90% certain it's an injector. Just to be sure it wasn't the MAP sensor, I pulled the connector for it and started the car. It threw a code and SES light for the MAP sensor voltage, but it had no affect on the idle quality/miss. I plugged the MAP sensor back in, cleared the code and started the engine again with the scanner running. Both left and right BLM and left and right integrators were locked on 128 while in open loop. As soon as it went closed loop, the right BLM shot up to 160 and stayed there while the left stayed right around 128, fluctuating only a bit. The right integrator shot up to 180 and was flipping around like mad while the left was right in the normal range. I could see the voltages for the right 02 sensor were much higher and fluctuating more than the left. As soon as I drove off, the right BLM dropped from 160 to under 128, and then started to slowly level back off to a more normal range. When I would come to a stop, the right BLM would just climb right back up to 160 and the whole cycle would repeat with every movement in traffic and stop. I really think I have at least one injector that is perhaps either partially blocked or starting to go bad. Enough to go lean at idle, but picks up the pace when energized under acceleration. While idling, it's forcing the 02 sensor to read lean, and being a batch fired system, the ECM is kicking up the fuel delivery for everybody on the right bank. The injector still isn't responding favorably so the ECM continues pouring it on. The reason I really think it's an injector is because I can feel the lean miss in the steering wheel and in the seat while it's idling. It's a subtle, rythmic "bounce". Goes away on acceleration, but comes right back at idle.

It's just GOTTA be an injector. They're 18 year old Multecs.

I'll be giving Jon at FIC a call in the Spring.

 

[gmjunkie]

It's just GOTTA be an injector. They're 18 year old Multecs.

I'll be giving Jon at FIC a call in the Spring.

:L:L:L No,It don't gotta be!!
Buts thats alright,I'm cleaning my car up to head to Florida Wednesday,after that I'll catch you guys in a couple weeks!!