Fiero 2m8 LT1 NX Roadster conversion (Page 42/46)
Fiero2m8 FEB 10, 08:45 PM
The fuel system was rerouted and new filter installed and although that was a good idea anyways, it didn't solve the problem.
I really should have known because the fuel lines always were fine before the engine developed this condition about 6 months ago.

The problem is still there when warm and it also stalls by itself unless kept at a high idle. (1000-1100 rpm vs. 700-800)

I hooked up fuel pressure guage and vacuum guage.
The fuel pressure is always reading 47-48 while cranking and idling.
When it won't start two squirts of fuel in the TB always works to start it.

I spent some time watching the vacuum guage while idling.
The guage moves from 12-15 Hg (just in the green section) right after you start it warm but as soon as the ECM tries to settle the idle down, the vacuum drops to 5Hg and it stalls.
When I raise the idle to 1000-1100 by adjusting the throttle plate it doesn't
stall, but when the throttle plates are closed and the engine is drops below 900 rpm it stalls everytime once the engine is at operating temp.

I might be having problems with the PROM tune or perhaps a vacuum leak?
The engine rebuilder told me that the cam he chose would affect my vacuum but I submitted a new data sheet to have a new PROM made and it worked for almost a year.
Maybe the 48mm TB is too small?

I really am stuck on the diagnosis and don't know what to check next.
Any suggestions would be appreciated.

Ryan
Fiero2m8 MAR 04, 12:37 PM
I'm hoping I've found the problem - a bad IAC.
Just ordered a new one and we'll see if that helps:


Last night I found this 1983 drawing - wow it looks like my Roadster with the moulded in flares, 16" rims, lowered and rear spoiler.
I had even thought about raising the door skins too!:


------------------

Indy Northstar-Stretch ~ LT1-NOS Roadster

Gokart Mozart MAR 04, 08:10 PM
Where did you find that?
Fiero2m8 MAR 04, 09:11 PM
Car Craft Magazine December 1983 article is called P-Dazzled.
Duane Kuchar created 6 drawings in all and they were reprinted in the 1st Quarter 1996 Fiero Owner Mazagine.
The six themes of the artwork drawings are:
1. Widebody
2. Front engine dragster
3. Roadster (shown above)
4. Hatchback
5. Speedster
6. Targa

I can start a new thread in General of them all if you like Dan.
Gokart Mozart MAR 04, 09:36 PM
Thanks, Ryan. I'm sure others would like them, too.
aeffertz MAR 04, 10:29 PM
Awesome hour and a half read. Amazing work, man. Keep it up and keep us posted!
Fiero2m8 MAR 07, 07:17 PM

quote
Originally posted by aeffertz:
Awesome hour and a half read. Amazing work, man. Keep it up and keep us posted!



Thanks for looking - I'm planning to work on the project tomorrow - stay tuned.
Fiero2m8 MAR 09, 08:51 AM
New IAC installed and the LT1 idles better but the no start when warm condition still occurring.
I'm going to do a data log with the scanner and fill out a new sheet to compare with the one sent to Mark at Street and Performance.
For some reason the engine doesn't get enough gas during a warm restart as two sprays in the throttle body solves the problem...

Here is the data sheet:

http://www.hotrodlane.cc/ne...93computersheet.html

I'm going to try unplugging the MAP sensor when it's warm to see if it will start.
Not sure what else to check, cause I changed O2 sensors and CTS already.
What else controls air/fuel mixture during warm start - I'm thinking EGR if stuck open?
Fiero2m8 MAR 10, 01:47 PM
Idle hunts 750-950 in park
Temp 191 degrees F
Voltage 12.5V
IAC 49 - Learned IAC 32
INJ P.W. 3.5 (both banks)
Spark advance 26 degrees
Fuel Trim 18 cell yes enable
LT Bank 2 142 - lean from 128
LT Bank 1 148 - lean from 128
TPS 0.64v @ 0% throttle (I adjusted it up from 0.35v)

Well I spoke at length with Mark today and he wants me to install new 24.9lb/hr fuel injectors.
I am also going to remove all header wrap and take digital laser temp readings of each header tube.
From there I can take more scanner readings and determine whether either of my PROM tunes will work or if a 3rd is required.
I haven't given up yet but the hard start when warm condition has been going on since last summer and I'm nearing the end of my patience
joshua riedl MAR 10, 05:15 PM
Is this a new problem? I had the same issue because I wired my ecm for switched power to the ecm constant power. It would start cold fine but I had to use the gas pedal to start it when warm.