Just started the motor and she's idling lean in open loop. 6E code in an 87 Vette, 24# SVOs at low to mid 40s PSI, 218/226 510/510 114 LSA cam, idling at 700-800 in Park. The only code I've changed was inj constant (25.9#), lower fan on, and higher tc lock. Barring vacuum leaks, where do I want to richen this up? I haven't matched the idle speed in the code yet. I could turn up the fp. I could lower the inj constant. What to do?

 

I went through the service manual idle set procedure today. Got everything perfect. Shut it down, restart, idled at 1400.

In open loop, it runs poorly - lean, low vacuum, low idle, IAC wide open. Once it hits closed loop, IAC closes completely, vacuum picks up, good AFR, good idle.

What is causing this? I don't know if IAC or lean condition is causing all the problems, although IAC would seem to cause the lean condition. Why is the IAC wide open in open loop and closed in closed loop? I must have to change something in my program, but what?

 

Have I been blacklisted? I need some help from people that have been through this.

I think this is mainly an IAC problem. In open loop, it's wide open and I've got low vacuum and a lean condition. Probably because the IAC is just a vacuum leak. In closed loop, the IAC closes and life is good.

Why is the IAC wide open in open loop? I haven't changed my idle speeds in the program, but my new mechanical idle is set slightly higher than the eprom's commanded idle. If the IAC is a stall saver, why is it opening all the way up at 700 when the car runs much better at 700 with it closed?

Am I missing something?

 

I am not as familiar with the 6E. Hopefully someone will jump in and give you some advice.

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

I think you have one or more of a few problems. I'll go through them one paragraph at a time.

You might need more spark advance while the engine's warming up. There's a table that adds to the spark advance at lower coolant temps, labeled "Cool Compensation Spark Vs. Load" in TunerCat and "Spark Correction - LV8/2 Vs. Coolant Temp" in GMEPro. Add several degrees at the coolant temps where your engine is warming up in.

You can add fuel in either of the open loop AFR tables, although the one vs. coolant temp is the one you should play with. Have you disabled your cold start injector? If not, did you match the open loop tables from your '87 bin to the '89 bin you're running now? How do you know that you're running lean in open loop? Scan tool? Gut feeling?

As far as the IAC, it sounds like it's maxing out in open loop to keep up the idle speed (which is higher at lower coolant temps). But once the computer goes into closed loop and takes control and the requested idle speed is lower, the IAC can close (or in actuality, extend to nearly shut off the IAC passage). What are your IAC counts in open loop and once the engine's fully warmed up and in drive? You should shoot for 10-20 counts when warmed up, and they shouldn't hit max (160) in open loop from a cold start-up.

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Greg Westphal
'87 IROC 305TPI/A4

 

Greg,

I'm a little confused. He said he is running lean in open loop. You indicated to add some spark. Adding spark will lean the mixture even more (spark firing sooner giving the charge more time to burn thus burning more fuel). Did you mean retard?

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

Yep, you're right in that adding more spark would lean it out, but I don't think I explained why I suggested adding more spark in his case as a possible solution. The computer takes away a bunch of spark advance while the engine is warming up (something like 15-17 degrees), and then gives it all back at once when the coolant temp has increased by 36 degrees F. It's line LC02D in the BUA hack, and I saw the same thing when I was running the '87 code. I'm not sure if it was still there when I switched to the '89 code, but I think it is.

Anyways, I found that adding several degrees (or even more if necessary) of advance to that coolant compensation table helped my engine idle better, needing less IAC (I was maxing my IAC out) and smoothing it out. Anyways, if he's running too rich in open loop (can't really tell since the O2 sensor isn't functioning then), then the additional spark helps. Of course, taking out fuel would work too.

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Greg Westphal
'87 IROC 305TPI/A4

 

Thanks Greg and Trax -

Timing - I'll look at the scanner to see where it is at startup and open loop. I can turn the dist to see what helps and then program accordingly.

Fuel - Cold start is disconnected. Lean according to AutoXray. I've thought about lowering the inj constant or changing AFR, but... read on

IAC - The highest it should try for is 900 rpm at 90 degrees, but then once past 110, it tries for 750 rpm, which is where the idle is mechanically set. After that, it should try for 600 rpm, which is why the IAC is completely closed in closed loop. The IAC is at 160 in open loop no matter the temp. This is killing vacuum and contributing to, if not causing, my lean condition. I'm leary to mess with the fuel until I've figured out why the IAC is wide open. But, I'm not sure whether the IAC is causing the lean, or the lean is causing the IAC. Now, throw in spark and I'm about ready to put in a carb!

 

I'd start with the IAC first. Pull off the throttle body from the plenum, take off the IAC motor and passage cover, and clean the passages inside the cover and TB as well as the tip of the IAC motor. See if this helps. If not, then open up the throttle stop screw until your warmed-up-coolant IAC counts are 10-20. Mine were around 75-85 when I first started burning chips (I had bumped up my idle 150 rpm), which was causing my IAC to max out in open loop while warming up just like yours is. This also meant that my IAC motor was only using 1/2 of it's range. Now I think the IAC only hits 140 or so from a cold start-up.

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Greg Westphal
'87 IROC 305TPI/A4

 

Cleaned the TB when I put it all back together. Burned a new chip with 10% increase in open loop AFR vs. coolant. Still lean in open loop. What to do now? Should I subtract in that table instead of add? Or just add more?

 

What are your IAC counts at idle when the engine's warmed up? If it's zero, then you might have the throttle-stop screw in too far, which means that you're letting in more air than you need to and the IAC can't compensate since it's already closed. If it's not zero, then turn the screw in so that your IAC counts are around 10-20. This will give the IAC more room to open up when the engine is warming up. If all else fails, or just as a simple test, add more fuel in to richen it up in open loop some more. Adding 10% more fuel isn't a whole lot, really...

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Greg Westphal
'87 IROC 305TPI/A4

[This message has been edited by GregWestphal (edited March 26, 2001).]

 

Dumped 20% more in. She got rich. Now I'll split the difference. Gotta put in that remote eprom. Pulling the memcal every day is getting ridiculous.

The extra fuel still didn't give her the open loop idle speed she wanted. Maybe I choked it. I had it adjusted so that in warm closed loop idle, I had about 5 IAC counts. When fans kick on, lights are on, etc. that goes way up. IAC is still wide open in open loop and I can't get to commanded idle. If I crank the throttle stop to get open loop idle, my closed loop idle skyrockets. Maybe it is in the timing?

 

Fuel doesn't help, has to be in the timing.

I changed the cool compensation vs. load table - I added 6 degrees at everything below operating temps. I believe that's the table to use, but winbin also shows a startup spark advance table. Is that only for startup?

While you're reading, any ideas why I have 0 in my inst fuel econ, avg fuel econ, and range displays and why my OD light is on since I switched to 6E in an 87 Vette?

 

Aaron, you added timing to the right table, and are correct that the startup spark advance table is just for startup. As far as the displays and OD light, I'm guessing that it's related to how/where your dashboard reads info from the ECM. If there's some sort of computer for the dash, you might need to swap it out for an '89 model. Beyond that, I don't have a clue.

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Greg Westphal
'87 IROC 305TPI/A4

 

I'm having the same problem and was just about to post a question. Mine idles (and runs) like crap until it goes closed loop. I watched this with my scanner. The instant it went closed loop, the idle smoothed out.

I'm not running the 6E (but think I'd better switch soon), but am confused about one aspect of your discussion. The ECM doesn't use feedback from the O2 sensor until it warms up (hence open loop / closed loop). This, presumably, is because that feedback is bogus if the sensor is not sufficiently heated. Therefore, aren't any statements regarding lean/rich during open loop operation unreliable since they are based on inaccurate O2 readings? So how can you really say you're running lean?

In the 32B, there are two tables for adjusting F/A ratio while in open loop (one vs temp and one vs load). Comparing '87 and '88 bins I have found that the '87 bin adds more fuel than the '88 (vs load). I had been using the '88 bin as my baseline, so I "installed" the '87 values in this table to see if it would help. I can't say that I see any real improvement. This suggests that richening the mix isn't the solution... ?

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'87 IROC 5.7l TPI - original owner!

 

Update - timing helped a bunch. My only concern is that my cold open loop idle is now at 34 degrees adv and she could use more.

As far as the mileage displays, I think I was given a misnamed bin. I'm going to try another 89 bin and see if it helps. If not, I guess I'll just have to switch to SD and lose the mileage anyway.

As for the O2, I've still got the stock exhaust (temporary!) and the O2 warms up and reads seemingly accurately well before the 5 min closed loop timer is up. The ECM isn't using it, but I can still look at it on the scanner.

Thanks for the continued help and I'll keep updating.

 

I have monitored a couple of "cold" (temps haven't gotten below 70 here for several days, now) startups to see what changes once the ECM goes into closed loop.
I watched the timing. It slowly increased from 14.6* to the low 20's, but made no sudden changes once the loop closed and the idle smoothed out.
I watched the injector pulse width. It idled at 2.2 - 2.3ms and didn't change once the loop closed.
I watched the rich/lean flag. It did indicate lean until closed loop. Then it jumped back and forth as usual.
If the mix was lean, then suddenly got corrected, why didn't I see a change in the injector pulse width? The airflow was constant, so to richen the mixture, I would expect to see the pulse width jump a little.
FWIW, the "cold" idle seems to be worse as the outside temperature is warmer. I'm beginning to suspect the IAC valve as a contributary culprit. Any suggestions?

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'87 IROC 5.7l TPI - original owner!