milano maroon

iTrader: (1)

I am hoping someone can help me with hot idle issue. Here's the details -

Engine is a HBP, 550 primaries / 1300 secondaries. Am running an ISC and most of the time I have a rock solid idle at about 950 rpm. But here's my problem -

After I drive the car, park it for a little while, and want to restart it I have a bad idle. Maybe 500 to 700 rpm and then it dies. Temperature per the PFC will read 95 to 105 degrees C.

I am attaching my current map and a log showing what happens during the hot start. Log should show 3 restarts and me trying to give it enough accelerator so that it stays running. Any ideas on what I need to do to fix this?

Had to attach the map and log as zip files. I can email them out if anyone can't open the zip archive.

Thanks in advance for any help you can give me.

Jeff

arghx

iTrader: (3)

I'm not sure how accurate the wideband reading is because it's probably not warmed up enough, but given the heatsoak condition I think you should first try to adjust your air temperature compensation. This is always tricky, because it can affect other areas of your fuel tuning.

You can also try tweaking fuel in rows P8-P10 at least as a test. Try to figure out if adding fuel will fix the problem, and then figure out how to implement that while minimizing unintended consequences (throwing off the rest of the fuel mapping).

I wonder if the hot start solenoid (fuel pressure regulator solenoid) is hooked up and working. That raises the fuel pressure if fuel temperature is high enough.

milano maroon

iTrader: (1)

Thank you for the reply Raymond. I was hoping you would see this.

"I think you should first try to adjust your air temperature compensation. This is always tricky, because it can affect other areas of your fuel tuning. "

I should have recognized this as heat soak but it never clicked. I have a fast acting sensor installed, but probably not fast enough. I guess the ideal solution would be to relocate the sensor away from the engine mass. But until I do that is this what you're saying? Go to Settings 2 / Inj vs Air Temp and increase the fuel compensation at 80 degrees? Maybe try a 5 percent increase to start?

"try tweaking fuel in rows P8-P10 at least as a test"

I don't understand that. The only time I was in those rows was when I was blipping the throttle to keep it from dying. My engine usually idles in rows P5 to P7 (a little lower vacuum than most, I assume because of the porting).

Plus this brings up a question - if the fuel and timing at idle is being controlled by the ISC will corrections to the Inj vs Air Temp table be used?

"I wonder if the hot start solenoid (fuel pressure regulator solenoid) is hooked up and working?"

I don't know what that is or where it is located. Can you give me some more information on that?

So right now I'll try increase the fuel in the Inj vs. Air Temp table a little and see what happens.

Thank you again for the reply.

Jeff

beefhole

iTrader: (29)

Use your ISC to bump the idle on a hot start. Also try using post start enrichment.

cewrx7r1

iTrader: (2)

The basis for all tuning starts with a hot idle.

Get the engine fully warmed up and stable.
Adjust air, fuel, and timing for best smoothest idle, not by AFR. This is affected by whether the ISC is working. TPS voltage is also important to be in range.

The larger the ports, the higher idle speed required.

Next is to adjust the cold start paremeters.
The hot wax rod/cold start assist affects this.

arghx

iTrader: (3)

Generally speaking the engine will pull less vacuum on a hot start. So it may be falling into those cells but only on hot start. I'm not sure about your specific engine though. It's something to investigate.

With idle IG control on, ignition timing oscillates around certain values depending on accessory load. Fuel is not affected. The ISC valve duty cycle isn't directly adjustable but the idle speed settings do affect it.
The fuel pressure regulator solenoid is among the whole mess of solenoids a stock car. Its purpose is to cut vacuum to the FPR on hot start, temporarily. This raises fuel pressure.

Let us know how it goes.

milano maroon

iTrader: (1)

Thank you Raymond, Chuck, and Beefhole for your replies and advice.

I raised fuel at INJ vs Air Temp at 80 degrees by about 3 percent. I'll see if that makes a difference. I guess it's going to be a tradeoff, increase fuel to compensate for a heat soak condition at hot idle vs. a little richer AFRs when engine is running at that temperature or greater. Correct?

I'll watch the logger and see where I am idling on a hot idle. Will look at increasing the fuel there if I need to.

Can you clarify something? When the PFC controls the idle if I advance the timing in the two maps a little bit does the timing range the PFC works in also change? Or does it have it's own map to choose from?

Thanks,

Jeff

cewrx7r1

iTrader: (2)

When the idle rpms are set to above 0 rpms, the ecu not only controls idle rpm, it also controls idle timing. This can be seen by looking at the actual timing and comparing it to what is in the maps.

When you go to a manual idle (idle speeds set to 0), only then does the ecu run the timing in the maps for the idle area.