hot start idle surge

[9secz]

My current tune provides quick cold (50 F) start, stable cold idle, and near-perfect driveability after a cold start. The hot idle was dead stable during, and at the end of a 45 minute drive today. However,

After being off for maybe 20 minutes, the engine refuses to idle smoothly. It starts quickly, but almost immediately starts surging. The surges increase in magnitude until the engine dies. The idle will work fine after a bit of driving.

The car has a rear mount intercooler (mid-engine) that (unfortunately) sits over the exhaust. I have added a lot of shielding, but my hot start intake air temp is typically in the 110 F range, even on a 60 F day. I'm wondering if MAT compensation is the root of my hot start idle problem. The thing is, my AFRs are not lean during the surge.

The MAT sensor is close to the throttle body and far from the turbo and exhaust system. It's the plastic body GM part.

Does anybody see what else might be causing the hot start idle surge?



Jeff

[onteera]

Try to adjust your idle advance settings. Spark advance goes up and down about 12-15 degrees, it may cause oscillation the RPM.

[9secz]

Try to adjust your idle advance settings. Spark advance goes up and down about 12-15 degrees, it may cause oscillation the RPM.

Thanks for the suggestion! I've tried putting the same advance in all the idle cells, but that screws up idle performance that is currently fine, which is most of the time. This surge only happens right after a hot start. I've tried setting the afterstart enrichment taper to 1000 cycles (only at hot start) to see if some extra-richness makes the engine happy. For some reason, possibly a tuning error somewhere, my engine idle is smooth only when AFR is in the high 12s. It *really* does not like 14 or leaner. I'll test the new ASE taper setting today.

I've played with injector timing between about 300 and 450 BTDC, but it doesn't make much difference.

Jeff

[subwoofer]

For some reason, possibly a tuning error somewhere, my engine idle is smooth only when AFR is in the high 12s. It *really* does not like 14 or leaner. I'll test the new ASE taper setting today.

I have been struggling with idle quality too. I have not looked at your .msq, but I have found that getting the VE table smooth and with the correct surface normal is essential to leaning down the idle. It does not take much variation in AFR to send it hunting when you are around 14.7, but a whole lot of variation to do the same while (overly) rich.

[fast930]

i had the same problem and was able to add fuel in mat percentage.my 930 was real bad after a good heat soak of 30 mins or so. i added 6% at 100 and helped tons. the intercooler never sees temps like that even here in so. fla unless heat soaked

[superchargingmachine]

I have the hot start issue on 2 cars now and have been unable to resolve the issue. As 9secz has described I have a cal that works good under normal driving, cold starts, etc. But, if I shut the car(s) off hot and come back too soon my AFR's go lean and the car(s) struggle to idle. If I keep the car running for a few minutes everything settles down.

My guess has always been that the IAT is heat soaked. This would lead to the calculated air denisty being lower than what is really entering the cylinders. What is the correct work around? MAT correction is going to influence things all the time right? But, I only need correction until things stabilize. What do the OEM's do?

Car 1:
1.6L 4AGE
Turbo
440cc injectors
EDIS
V2.2 MS
tried 2 IAT locations, clsoer to the valve was best but does not fix the problem completely.

Car 2
1.5L 5EFE
M45 Supercharger
440cc injectors
MSD 6AL - digital
V3.57 MS
IAT near head

[16vboost]

For some reason, possibly a tuning error somewhere, my engine idle is smooth only when AFR is in the high 12s. It *really* does not like 14 or leaner.

I think your injector dead times are too low. Where did you get these values from?

I think they're too low because I had a similar experience where I could not idle above 12.5:1. Also on over-run the engine would go full lean. I've increased the dead time and can now idle at 14.7:1. What does this have to do with hot starts? Naturally, your PW is much lower once the engine is hot (not to mention hotter air is less dense and requires less fuel). You'll have to re-tune VE once you mess with dead times but just try it around idle at first.

-Alex

[superchargingmachine]

I will have to get the car out and give this a try. Would anyone have dead time information for Toyota 7MGTE 440cc Denso Injectors?

[16vboost]

I noticed in your tune you have slightly different dead times for each injector. How did you get these numbers?

-Alex

[9secz]

I noticed in your tune you have slightly different dead times for each injector. How did you get these numbers?

I tested each one with my modified injector tester. Here's a vid of the setup:

http://www.youtube.com/watch?v=KlnS67s8aGQ

If my pc is good to me, my Excel data file should be attached. Never mind, the site won't accept the file.

Jeff

[16vboost]

That test setup looks awesome. I spent lots of time with the 1 squirt vs 2 squirts method of tuning injector dead time and got it right at .890ms. I finally decided to just raise it to see what would happen and settled on 1.1ms. It really helped my idel and EAE over-run conditions. I think it's a hack, but it helps when your PW is below 2ms. Are you using those 1200cc injectors in the car? What's your maximum duty cycle at full boost / rpm? Can you lower your fuel pressure to get a longer idle pulse width?

You said your car doesn't go that lean after a hot start, but won't idle smoothly at above high a 12 AFR. So if it gets into the 13's after a hot start, you're in trouble. I think your first course of action should be to make the idle as robust as possible, then tweak MAT correction and ASE to try to make up for most heat-soak conditions.

I'd attack these areas to make the idle better
1. Make sure you can idle at 15:1 if you need to (play with idle PW and injector dead times)
2. Don't make your ignition table flat, it should go from 15 deg at idle to 4 degrees at idle rpm and 100 kPa. Less advance with higher MAP!
3. Increase your MAP lag factor to 100% or as close as possible.

For the heat-soak tweaks I'd do this:
1. For air temperatures beyond your normal operating range, raise the heck out of the MAT correction (somewhat smoothly of course).
2. Increase your ASE duration for elevated temperatures (temps beyond normal operating that is).
3. Increase your ASE percentage as much as you can without ruining your cold start performance.

You know your idle is good when you can take off in first gear without using the gas.

Keep us posted
-Alex

[Yoeddynz]

Digging up old threads. My Viva has been having the exact same issues as the OP.

My inlet setup consists of a K&N filter onto a large alloy pipe that runs up to a 90 degree bend into my throttle body. This is just behind and above the radiator. I have a plastic GM IAT insulated from direct contact with the alloy by some 2mm foam. This sensor is mounted under the pipe just out of sight, about an inch down hill from the 90degree elbow. For a better idea please see here...





The car will start fine hot or cold. It idles fine normally, however due to the above mentioned 'possible heatsoak' problem I have ended up setting it to idle a bit rich at around 12.5- 13 so when I get the heatsoak situation it doesn't effect the usability. However this then means that for most of the time its too rich at idle. I want to fix the cause or find a way to tune around it.

The heatsoak problem will rear its ugly head after the car has sat for maybe 10-20 mins when the engine is at full temp. On stinking hot days its at its worst.

I have read the above posts and I'm still not that confident in playing with the MAT settings, or even fully understand them. I am sure there must be a way where I can add fuel for just the first half minute or however long I need in order to stop these lean surges. Once the car is moving again or has even idled for a minute or two its fine again, but too rich due to my current setting to try and combat the worst case scenario.


9secz.. I am wondering if you solved your issues and how? If anyone else reading this thread who have had similar problems and managed to tune them out then ideas or advice would be great. Or links to good threads on understanding MAT correction etc would be great too. I have some suggestions in the past like ignoring the IAT temp at startup. However my issue is not starting when hot, which is fine, but instead having and unstable, surging idle for about 20-30 secs after startup. From what I understand 'ignore IAT at startup' will only affect the startup and not the time after?

Cheers,
Alex

[superchargingmachine]

This is a blast from the past. I wondered if this had ever been resolved. I always thought a fixed fuel rate on start up based on clt or iat with an adjustable timer would correct the issue. I haven't messed with MS for a couple years now. Good luck.

The was the only issue I was never able to resolve.

[Yoeddynz]

Yeah its currently my only tuning issue on this car.. and it is an annoying little thing too.
I am sure there is an easy fix somewhere!

[slow_hemi6]

I have had mine set up using the Ignore MAT during ASE recently. I have 77C and 100C as my last 2 coolant rows with 0 in the Enrichment % and enough in the taper to give me about a minute or so of ignoring MAT after start up.

[Yoeddynz]

OK.....I'm trying to picture that..

Could you possibly put up a screen shot of that?

I'm gonna delve off into TS and have a look to see if I can work out what you mean

[Yoeddynz]

OK I have had another look and scratched my chin. I think I have worked out how the Mat correction thingee works!

This is my current table...



So what I think is happening is this..

Say I drive to the supermarket. When I arrive I turn the engine off and go do my shop for the finest sausages and beer one can buy. Meanwhile as I'm inside picking between dark malts and Ipas the heat inside the engine bay soaks into the big alloy tube between the filter and the TB. The IAT sensor positioned just down from the TB gets warm itself (even though its plastic its still going to warm up).

I return with my goodies and start the car. The ECU now sees a much higher temp than what is actually getting drawn into the engine and pulls some fuel out. Lets say it thinks the inlet temp is 50 degrees. According to the MAT correction table above it will pull 10% of fuel. Hence the engine runs lean for a minute or so until the pipe and the sensor cool down. Then it slowly returns to normal.

So If I play around with that table and alter the graph so it doesn't pull so much fuel I should see improvement. Considering my car is N/A and we never get much above say 35 degrees on the hottest days here then I should be fine doing this.

Is this correct? I will try it out and see.

[slow_hemi6]

Yes that will help combat the lean restart from heat soaked sensor issue. I don't let mine correct below 92%.

[Yoeddynz]

Yay- I'll give it a go today.

[Yoeddynz]

It worked! One minute spent flattening off the curve from about 30 degrees and the car ran perfect after a hot start having sat a while. Very happy indeed. I can now adjust my idle back a bit leaner on the VE table and with a bit more tinkering it should be all good.