Off-idle stumble and testing/calibrating/adding sensors

[alangbaker]

Greetings, folks.

I've finally got my Van Diemen RF98 Honda on the track, and for the most part, everything is running great, but I'm wondering about a couple of things.

First of all, the engine stumbles when you first open the throttle from idle. It's not bad once everything is fully warmed, but when the car is first started, the engine will die if you open the throttle unless you're very, very careful. Has anyone got any ideas on what might be causing that? The engine assembly manual makes particular note of the calibration of the throttle position sensor (TPS) and I'm wondering if that's the likely culprit.

And can the other engine sensors be easily tested, or is it a matter of simply replacing if you suspect that they might be bad?

I'm not actually concerned with the engine's performance at the moment. One of the other guys in the club has a pretty fresh Loyning engine and we seemed pretty equal (I'm running the 30.5mm restrictor per SCCA rules). A little reading in this section of ApexSpeed suggests that a dark exhaust pipe is normal, is that right?

Anyway, any and all thoughts, opinions and advice very gratefully accepted.

[Hardingfv32]

Dark pipes if using un-lead fuel.

Brian

[alangbaker]

Thanks... ...I thought so, but I wasn't sure.

[Roux]

Even in hot weather mine needs a few minutes of warming up before the stumble goes away. Once warm no issues. In really cold weather a few restarts might be needed. A coin or washer between the throttle and the stop can help warmup a bit. My exhaust for some reason is light tan. Over the top Swift style exhaust. Filter is clear, have not looked at pressure, but I should start logging that

[problemchild]

Even in hot weather mine needs a few minutes of warming up before the stumble goes away.

It is a race engine, so I do not believe there is any program in the ECU for driving when cold. We find that 140 deg WT is required to drive it to the grid. Then it is good to go. Ours normally stall within 2-3 seconds when first started cold. On the 2nd start, if it makes it to 4 seconds, then the ECU, increases the idle, and it will stay running. Some engines and cars have slight variations in this process, but most have needed 140 degrees.

The LED diagnostic program seems good for basic troubleshooting. If you don't know what this is, get someone who races with a FIT engine to show you the 8-page HPD Electronics manual with directions and codes. The only one I know is 5 flashes means low battery voltage, and gets tripped on start up if you use a small battery.