daveS

I just installed a 430hp LS3 and 4L65E trans in my hot rod, with the GM supplied computers and wiring harnesses for the engine and trans. The car fired up in only a few seconds and I've driven it a few miles, but it has a low idle speed and a bit of what feels like surging. The engine has died several times, when I let off the gas, approaching a stop sign.

Any ideas what to start looking at? The MIL light is not on.

I have hooked my laptop to the trans computer and it shows an idle speed of about 600 rpm, but it seems lopey, compared to my new Corvette.

Edit: Also, when I started the car in the shop, this morning, the engine idled OK, but still slow, until the ECM turned on the electric radiator fan, then the engine died again. It will start right back up in a second, anytime after it dies.

KENS80V

iTrader: (16)

Was there provisions in the harness for a speed signal?

daveS

There's a tachometer wire (but I have no tach yet) and the trans has a vehicle speed output to it's controller. I changed the trans setting for the correct gear ratio and tire diameter. The trans controller will display both engine and vehicle speed, coolant temp and trans temp, when hooked to my laptop.

It's my understanding that the connect and cruise engine computer may not be "tuneable".

Next time I get the car out, I'll hook my laptop to the trans controller (made by PCS) and watch all of the available gauge outputs.

daveS

Late yesterday, I checked the coolant reservoir and found that it had been sucked dry (probably a pint) when the engine cooled down from it's last run. I refilled it and put about another quart of coolant in the radiator. It's been hard to fill - I've had to pour very slowly, but it always got to a point where it just wouldn't take any more, so I assumed that the system was full.

Today, the engine started idled nicely and the radiator fan never came on, so either the computer learned something from the previous run or the problem was a shortage of coolant. It was only about 25 degrees outside, so there should be plenty of cooling available. The laptop readout was showing 199 degrees for the coolant temp and the fan is supposed to come on at 207.

LSX Power Tuning

iTrader: (4)

It just needs a good tune. I have re-tuned several of those in the last few months. All of the customers had the same complaint, driveability.

Old Geezer

iTrader: (3)

Some of those GM pkges have a warning that tuning, voids the warranty.
A bit absurd....

daveS

Thanks for the responses.

Just this morning, I figured out that the idle problem starts the very second that the ECM activates the electric cooling fan. If the car is already idling when the fan comes on, the engine dies immediately. Restarting is never a problem.

If the ECM is tunable, I'll have to start looking for a tuner in the Denver/Loveland/Fort Collins area, or see what it might take to do it myself. I'm new to computer controlled engines, but have decent computer skills. Before I retired from engineering, I did a lot CAD drawing and programming CNC lathes and mills.

My hot rod is not street legal yet and can't be driven to a tuning shop. I just drive it around a 1-mile loop in my rural neighborhood.

daveS

I've read some more on this topic and found a warning about having the air cleaner located in the air stream coming off the electric radiator fan. I have this type of setup, so I placed a piece of sheet metal between the fan and the air cleaner, to block the hot air flow. That seemed to help a lot. A least now, the engine doesn't die immediately after the fan comes on.

I'm still having some problems with low idle speed and some surging at moderate speeds. I'm going to put some more miles on the engine to see if performance improves.

01WS6/tamu

iTrader: (37)

May have to just drive it a while the pcm has parameters it learns as it's being driven and adjusts itself accordingly while doing so. This is why they act goofy after disconnecting the battery on initial restart until it has been driven a few miles and or allowed to idle in conjuction with being driven.

I've installed several of these engine packages and found the base gm tuning to be pretty dang good for what it is. Of course it's like all OE package tunes it's on the conservative side so they do benefit from a full custom tune but for a hit the key and roll with it they are pretty spot on.

daveS

I moved my MAF sensor further up the intake snorkel, just above the radiator hose, but that didn't help. I still had a slow idle and stalling as I approach a stop. My shield for the air cleaner has cured the problem with air flow from the radiator fan.

I'm also working on a new snorkel that will use the current silicone 90 attached to the throttle body, along with an aluminum 90 and 10 inches of straight pipe, located above the intake manifold. I won't be pretty, but it may work better.

I decided to buy HP Tuners VCM suite and do some tuning myself. So far, the only thing I've done is change the 550 rpm idle target speeds to 600 and change the min idle speed to 600. I drove the car long enough to be the coolant up to full temp and the car never died approaching a stop, so at least it drives better. GM apparently expects the engine to idle properly at 550, so I assume that some other parameters need to be altered to fix the problem properly.

I made a scan of the engine idling, but have no idea if the MAF readings are normal.

http://www.hptuners.com/forum/showth...e-idle-problem

LS3AEROCPE

I just put it in my 87 M/C Aero. The first start its around 800 rpm but settles to 500 rpm. The cold air intake tube must be away from the raidator and the map sensor installed inside the longest flat part.

daveS

I built a new air intake snorkel, that has 11" of straight tube, with the MAF sensor right in the middle. The air cleaner is up above the intake manifold, far from the radiator. That exceeds the GM requirements, that came with the engine. They suggest a 6" minimum length, with the sensor in the middle of the run.

I still had problems with engine stalling, so I hooked up my computer and found that the minimum idle speed table didn't get changed to 600 rpm across the board, to replace the original 550 rpm values. I edited the table to have all 600 rpm values and it seems to drive OK, but not much different than it did with my old snorkel that has no straight pipe. The MAF reading at idle is about the same .7-.8. The throttle open percentage is 18%. Does that seem like a normal value for the mild 430 hp cam?

I'm happy as long as the car doesn't stall and seems to accelerate well, right off idle, which it seems to do.

I was thinking about editing the MAF table. If anything, I'd guess that the AFR is rich ( I'm at high altitude) and/or the spark advance is a little low (around 14 degrees). I may try a little less frequency, for a given MAF reading.

blyne3

Try it with the MAF unplugged and see if the problem goes away. The MAF is really sensitive, air turbulence is detrimental to the reading and will cause all sorts of problems like rich or lean and it is also measuring air temps, so being in the flow path from the radiator may cause issues.

daveS

Here's my new intake snorkel.



Below is a link to my latest scan with a 610 idle speed. Before I added another 10 rpm to the idle speed, the engine still had the occasional stall upon a stop sign approach.

http://www.hptuners.com/forum/showth...782#post341782

2xLS1

iTrader: (25)

You might consider using an airflow straightener from saxonpc in front of the MAF.