Hey guys,

I have a customers L98 that during open loop idle it is real lean (reading 17-19.5:1 A/F).

The L98 was transplanted into a 1987 K5 Blazer (beautiful truck) and I have dialed him in for all of the driveability issues and max power at 256HP & 290ft/lbs at 24.14mb atmospheric (welcome to 6200' above sea-level). The motor is FAR from stock. Sorry for my ignorance, but I do not have his build sheet in front of me. He has an intake, heads, larger...but not too agressive cam, forged pistons 10:1, crank, etc.

The problem is when it is cold or just in open loop idle it is super lean and has a terrible idle. When the 02 (heated) wakes up it will settle in to a nice idle and hover between 14.2 and 14.9:1 A/F. The main problem is now that the COLD weather has arrived in Colorado it BARELY wants to run in the morning and my customer is not happy.

Any help would be GREATLY appreciated!
-Kenny

ps...I am using TunerPro RT and Moates Emulator to tune.

 

Well, there's a few "L98" computer and software combinations, but, as long as the VE or MAF tables are set to deliver roughly BLM=128, then there's usually a warm-up enrichment table to tweak. It may be called "open loop" afr % change something something. There's also a "start-up" enrichment available that is used for the first few (5-15) seconds after starting.

I'm not a moderator, so I won't harass about it being a non "DIY," but be prepared for it.

 

I did see the open loop AFR % vs TEMP and also open loop AFR % vs MAP. I tweaked the TEMP table and hopefully in the right direction. I made the assumption that the higher the number the higher percentage of PW in that temp range seeing is on the table the value climbed as the temp reduced.

I will look for the start-up enrichment value as well tomorrow when I return to the shop.

Sorry if this is in the wrong section or if I was out of line posting on this forum with help on a 3rd gen motor combo.

 

What does it read during warm open loop idle Still Ok? The first step to getting the cold enrichment right is to make sure it delivers the proper fuel when warm. Itll be harder to check up on the enrichment when the engine is cold. My experience is that the WB isnt that accurate as the combusion efficiency isnt up to speed on a cold engine. I was drowning my motor in fuel at startup and didnt know it untill the motor warmed a bit. Started at 12:1 and sunk into the upper 10's once it started buring some of the fuel that was being put into it. As for the cold enrichment, Id probably just set it to where the engine runs best and doesnt smell gassy or blow smoke.

Also, any chance of some profit sharing, here?

 

Profit sharing? Sure just like most of the aftermarket companies there is a $5000 buy in...then you need to have 100 of my chips on hand, etc etc! Just kidding! Seriously kidding...just looking for some good old fashioned tuner help.

Well like I said once the Heated 02 wakes up it idles perfect and hovers around 14.2-ish to 14.8-ish and stays there till normal operating temp. When the motor is warm and Open loop it struggles to hold a good idle and is still lean. I did notice in the AFR % vs TEMP that the value above 20* was the same value all the way up to full high temp at 9.xx. Lower than 20* and it was steadily climbing up to 35.xx. To let you know the WB is on my dyno and ready for sniffing duties when I fire the truck up.

BLM and INT seem locked at 128 until the 02 wakes up and then settles and holds at 127-128. The 02 sensor while it is in open seems to stay right around 350-400ma until it wakes up and spikes to 800 and then settles.

Thanks for the input guys!
-Kenny

 

If your tuning, just make sure your in open loop so you dont have the computer making corrections. The computer can correct for alot so it can make a tune thats way off run ok. If it runs poorly in open loop, then the VE tables are off.

As for the profit sharing comment, thats in regards to you being a tuner. A lot of people on here have gotten burned big time by the tuners and other people looking to make a profit off of their work and knowledge, so you may get some flak about the fact that your tuning for profit. Nothing personal, but I can definatly understand where theyre coming from. Essentially right now your getting free help on your customers car.

 

Honestly I am not looking to offend or burn anyone. I am a part of numerous forums that I help others (private and paid tuners) dial in diesels, turbo gassers, methonal conversions, 2 stroke shifter karts, EFI motorcycles, stand-alone EMS, and plenty more. I did not realize that asking for assistance on a poor running open loop L98 might get folks in a stir. My sincere apologies and I will take what was mentioned above and see how it helps.

I truly appreciate the replies,
-Kenny

 

I would say that if its lean in open loop then its likely the VE tables are off. Pretty much all tuning should be done with the engine fully warmed and in open loop so you can see whats actually happening. Right now it sounds like the computer is correcting for the issues once it enters closed loop. With the speed density computers, the VE has to be recalibrated even for small changes like timing. Large changes like stated above can leave the tune way off as the actual and reported VE are very different. It'll probably take at least a few iterations to get the VE to where it should be, although it could take many to finally get it dialed in. The low barometric pressure in CO will also play a part as the VEs will be slightly higher there then at sea level, due to the reduced pressure at the exhaust. With a high flow exhaust, though, this shouldnt be as much of an issue as it would be with the factory exhausts.

Once that is done, then you may find that the cold start issues clear up on their own once the VEs are in line. Dont touch any of the cold start untill the warm idle/run is ok or you may find it pig rich on startup once its tuned.

 

If this is SD and it happens in very cold weather, it sounds like your MAT Delta Inverse Table is off. This is caused by one or both of the following:

1) If he has a relocated MAT/IAT sensor, then you MUST readjust your MAT Delta Inverse Tables. Do some searches on the subject as I did a lot of research and posts on this and RBob did further research.

2) The EGR is not functioning by the exceedingly cold weather and you need to adjust the EGR enable/disable temp. However, the "tune" is expecting an EGR and this affects it.

Even if he doesn't have a relocated MAT/IAT (i.e. still in the plenum), he still may need some adjusting of the MAT Delta Inverse Table.

I encountered all this 5 years ago when we hit -10*F weather.

 

He also mentioned that the motor is far from stock, so Id guess that its probably a combination of issues. IMO, I would still start with the warm open loop tune. If thats off, then nothing else matters. Once thats complete, then work your way back to the things that will affect cold engine operation.

In laymans terms, the MAT delta inverse table basically is used to blend the IAT and CTS temperatures to get a true air temp to estimate the air density. This shouldnt affect the immediate cold start as the engine and IAT temps will essentially be the same, but it can really screw up the rest of the tune as the engine and intake air temps diverge. Keep in mind that the inverse delta term is based on airflow, which is calculated from the VEs, so if those are off, then that will also be off. Again, if I where you, Id set the engine to run in open loop, put it on the dyno, and start tuning the VE tables. Those are pretty much the foundation of the entire tune.

 

Yesterday I dialed in the VE tables in open loop. She idles as smooth as can be in open loop now. I loaded the truck for all the cells in open loop for the tune. Then let her cool down for about 3 hours while I worked on another clients car. I then did a "cold" start and it idled smooth all the way until the 02 came into play. It seemed to be hunting and following the 02 swing from lean to rich for about one minute and leveled out. When reflashing the 27SF512 chip it took a crap because of my burning station. I ordered a different and new station from Moates yesterday and thankfully they answered my begs and plead for it to be shipped out last night to arrive this morning. I will redo the chip when it arrives and test the true cold start as it is 6*F this morning.

I will go back and check everything you guys mentioned. I think it is pretty well set at this point. My mistake for not dialing in the VE tables in open loop and up to temp. I learn something new everyday!

THANKS GUYS!

I will post back how things are looking later today.

-Kenny

 

Hunting on idle can be a sign of the IAC out of adjustment. The "OEM" limit fot he IAC is too low when you modify an engine and usually needs to be "bumped up". The bigger the variation between the IAC setting and the rpm (which can get high with a cold weather), will make the "hunting" more pronounced.

I like to set the IAC to 50 rpm less than my desired RPM when hot.

Try setting the IAC as above and MAYBE a slight reduction in the "very cold" idle speed parameters.

Cold weather tuning is seldom discussed here as so few people actually tune their cars for severe cold weather (due to their location seldom gets that cold), and most guys don't drive their cars in severe cold weather.

The only reason I found certain things about cold weather was I had to drive my Firebird one winter when I moved to a location that gets "stinking cold". After that first year, I got a "second car" for winter driving.

 

Do you happen to know what the min temperature is for closed loop in your cal? I doubt its set to anything extreme, but its worth a check if your getting some initial surging with the motor still cool. After that, you may need to dig deeper if this is an issue for the customer.

Im using a later model PCM and they had the min temp for full closed loop set to something like 2 deg C. With my unheated O2, this would cause the AFRs to swing wildly from 19:1 up to around 12:1 as it would go into closed loop way too early. The PCM kept the idle steady, but it would start misfiring like crazy when it got to 19 and 20:1.
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Can you elaborate a bit on how the $8D idle routines work? Im used to the PCM, which has everything based on flow and uses standard proportional, integral, derivative terms to control the idle. I remember the $8D routines looking a little odd when I glanced at them.

It could be an issue with too much gain at low temperatures, if the $8D uses temperature based gains.

Or, it could be too much gain in the closed loop O2 calibration. KAZ, what are the high and low reported AFRs from the WB when the car enters closed loop?