454 XL TBI rpm issue

[waybomb]

I saw sone discussion of the anti-siphon valves; did you replace them?

[390Express]

Source of the post I saw sone discussion of the anti-siphon valves; did you replace them?

Fuel delivery is good. Motor has good fuel pressure while it's stalling. Seems like the ignition ecu is being turned off, or triggered to turn off by a sensor.

[390Express]

Picked up a scanner. Motor had a fault for a Electronic Coolant Temp sensor. Sensor was reading -39 when it was 85 out. Thought that may be the issue, as the ECT effects fuel flow, & Map sensor, but no dice. Put in a new one - no difference. Of importance, according to the ECU, all sensors are in working order, and there are no fault codes.

Replaced the top fuel filter (metal can style), took apart the antisiphon valve just to rule it out, motor has spark at the coil and distributor as it's stalling. I don't get it.

[km1125]

Did you eliminate a second crank sensor as a possibility?

[390Express]

Source of the post Did you eliminate a second crank sensor as a possibility?

Where would it be? ECU says all sensors functioning properly, so I doubt it, but I'd give anything a shot.

I swapped helm harnesses today (so the port motor runs off of the starboard switch and gauges, the starboard motor runs off of the port switches and gauges), no damn difference. It's something after the 9 pin at the motor. Seriously considering buying a new wiring harness, but if that doesn't fix the issue I'm going to be livid. I had a pretty damn good mechanic come take a look at it. He's stumped as to how I can have power to the distributor, power to the coil, spark, and fuel, and the motor still stalls. Runs great while it's running, but stalls after 10-30 seconds run time, no fault codes, no issues.

I thought it may have been low on gas and simply running out, but I put 20-30 gallons in since. I set the fuel level sensors to read empty at 21.5" (24" tank, 2.5" above the bottom of the tank), and the new fuel level sensors read 1/4 tank, which makes sense, it has 40-60 gallons in it. Took apart the antisiphon valve, aside from a small amount of gunk, it was clean and functioning fine. New Racor 110a filter, new fuel filter, new can filter at the top, I'm stumped...

Scanner says proper injector pulse and fuel flow, no low fuel pressure warning.

[km1125]

While you have the scanner, look at the IAC on both engines when you start them up and run them for the first 30 seconds. I'm wondering if the engine ECU sets the idle higher (via IAC and richer injectors) then after 30 seconds or so drops down to normal. However, if your throttle plate setting is too low or too high the engine could run either low on airflow or run too lean because of excess airflow, and stalling.

Might do a visual compare of where each throttle plate is set when it's at idle setting. There should be an allen screw that adjusts it, just like an old carb idle screw.

[390Express]

Source of the post While you have the scanner, look at the IAC on both engines when you start them up and run them for the first 30 seconds. I'm wondering if the engine ECU sets the idle higher (via IAC and richer injectors) then after 30 seconds or so drops down to normal. However, if your throttle plate setting is too low or too high the engine could run either low on airflow or run too lean because of excess airflow, and stalling.

Might do a visual compare of where each throttle plate is set when it's at idle setting. There should be an allen screw that adjusts it, just like an old carb idle screw.

I'll look for the throttle plate setting. The scanner is pretty cool. It has a throttle position indicator, which is 0 at startup, and moves up in terms of percentage as you push the throttle forward.

I believe the IAC value is something like 1.4 or 1.6, it's the nominal position, and it deviates from there up or down as the valve opens and closes. Seemed to be operating normally. Injector pulse values look good, but I was roasting my ass off last time I had it hooked up. I plan to head down there this evening for a bit around 6 or 7pm.

Another tech told me to look at the ignition module and the small coil harness between the coil and distributor. I suppose I could try swapping distributors, but the damn distributor is brand new A/C Delco, I really can't see it being bad, but weirder things have happened.

[km1125]

The throttle plate setting is different than the throttle position, as the throttle position is just the sensor, which can be calibrated or adjusted to the individual throttle body. Some you can calibrate as easy as turning the key on and moving the throttle from 0 to 100% and the ECU will automatically adjust. Others need to be physically adjusted by loosening the mounting screws and rotating until you get a specific resistance on the leads at idle.

Did you take the throttle bodies off and do anything? I thought I had read somewhere that you rebuilt them (or one of them?), but I might be getting confused with another issue.

The IAC value should change as the throttle moves up and down, or the idle changes due to load. I've just seen them in counts from 1 to 127 or 1 to 255 but I guess they could use whatever range they wanted. The key is to compare port to stbd.

[390Express]

Source of the post The throttle plate setting is different than the throttle position, as the throttle position is just the sensor, which can be calibrated or adjusted to the individual throttle body. Some you can calibrate as easy as turning the key on and moving the throttle from 0 to 100% and the ECU will automatically adjust. Others need to be physically adjusted by loosening the mounting screws and rotating until you get a specific resistance on the leads at idle.

Did you take the throttle bodies off and do anything? I thought I had read somewhere that you rebuilt them (or one of them?), but I might be getting confused with another issue.

The IAC value should change as the throttle moves up and down, or the idle changes due to load. I've just seen them in counts from 1 to 127 or 1 to 255 but I guess they could use whatever range they wanted. The key is to compare port to stbd.

I rebuilt the "business end" of the throttle body, but the rebuild kit is more or less just for the top half. They give you a new base plate gasket, but nothing else. I didn't really see any reason to get into the base plate. Nothing was leaking gas, no play in the throttle, and no vacuum leaks. Both TBIs have new regulators, & O-rings. The motor that is now stalling has brand new injectors, but it was running great with the new injectors for two months. It was running a bit rich when I bought the new injectors, but it was perfect, before it developed this stalling issue. I could swap upper halfs easy enough, but the injectors fire as it's stalling, and they're spraying nice. I really don't think it's an injector or TBI issue. IAC nominal value is 130 according to the scanner. I thought there was a decimal in there, but that's the voltage readout, which is also good. IAC moves from 80-130 while it's running, no real difference as its stalling. From what I can tell from digging into the MEFI 1-2 diagnostic manual, there's nothing in the ECU that provides a higher idle, that would otherwise make it stall later.

Swapped the coil to distributor (two wire) harness, ignition module, fuel pump relay, and MAP sensor today. I considered swapping the throttle body, or at least the upper half, but I really don't see the advantage. The fuel pressure reads fine, the injectors spray fine, and there are no vacuum leaks. Perviously swapped the ignition relay, & starter relay. IAC and throttle position sensor are operating fine via visual inspection and scanner readout.

Ran the boat off of the dingy tank. No real difference, but it was nice to see fuel pumping as the motor stalled and after. Return line was flowing fine; nice steady stream, no disruption in fuel, brand new marine gas, still stalled... Confirmed that both motors are operating fine off of the same fuel pressure (12psi)

The only real noteworthy item left on the ignition side is the distributor. It's brand damn new, AC delco distributor, cap and rotor, but stranger things have happened than getting a bad electronic device out of the box. Still weird that the coil and module have voltage and spark as its stalling. The only thing that I noticed from the video posted above, is the variation in timing before it stalls. It more or less turns into a solid timing light right before it stalls, which makes no sense. The motor is still turning, it shouldn't get stuck on a triggering event inside the distributor. Looks like that may be my Sunday morning project.

[km1125]

Source of the post From what I can tell from digging into the MEFI 1-2 diagnostic manual, there's nothing in the ECU that provides a higher idle, that would otherwise make it stall later.

It's not really the higher idle, but all engines have to run a bit richer when starting from a cold start. Fuel injected engines run rich for a period of time, which can be a timer or by measuring coolant temperature.

The ignition observations are interested. Seems like you need to understand what's going on there. Can you put the old dist in there for testing?