Crank Position Sensors LT1

[mikeg205]

What do spark plugs look like... post pic please

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[jlarkin.41]

What do spark plugs look like... post pic please

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I will pull them this weekend and snag a picture.

Is vapor lock a possibility? I have read a few times that vapor lock shouldn't be possible on the EFI LT1, but it sure seems like a similar set of symptoms. I would be weird however that it just started as I have never had this issue in 7 years with very little change in my boating habits.

[jlarkin.41]

What do spark plugs look like... post pic please

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Tested quite a few things today. Plugs looked ok in my opinion for having ~70 hrs on them or so. Tested voltage on the MAP sensor and TPS and they appear to be doing what they are supposed to. Checked resistance across the ECT again at ~130 deg F it was about 650. Checked all coils for signs of arcing, cracks or corrosion and all looks good.

Left my fuel pressure gauge installed this time and left the stick pins in the connector for the ECT. Hoping to see something the next time it happens.

I should note, it did throw a code 14 (low ect) but I believe that’s because I unplugged the ECT while it was idling rough last time to see if anything changed.

[mikeg205]

Looks like 3 are not firing. 1 had some activity. 2 seem brand new. Seems like running on 5 cylinders

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[jlarkin.41]

My spark tester shows spark on all cylinders and it runs phenomenally after it starts. I hit 49 mph today, I doubt I would be able to do that on 5 cylinders.

The darker colored plugs came from the rear four cylinders.

[JimN]

The plugs that are light tan indicate a lean condition- they look normal for a car, but not for a boat.

Find a way to run diagnostics with a Tech 1 or something similar- doing it with a meter will just take too long and it will annoy you.

Vapor lock IS a possibility because the fuel pump is at the engine and not in the tank. Make sure the fuel line hasn't collapsed or de-laminated- it's getting close to 30 years old and ethanol isn't a good thing for that particular type of hose. Check for a fuel filter at the tank, too. If you find one and didn't know about it, I doubt it's allowing good fuel flow. While you're there, check the fuel pickup, check valve (if it has one) and the fuel shut-off.

[jlarkin.41]

The plugs that are light tan indicate a lean condition- they look normal for a car, but not for a boat.

Find a way to run diagnostics with a Tech 1 or something similar- doing it with a meter will just take too long and it will annoy you.

Vapor lock IS a possibility because the fuel pump is at the engine and not in the tank. Make sure the fuel line hasn't collapsed or de-laminated- it's getting close to 30 years old and ethanol isn't a good thing for that particular type of hose. Check for a fuel filter at the tank, too. If you find one and didn't know about it, I doubt it's allowing good fuel flow. While you're there, check the fuel pickup, check valve (if it has one) and the fuel shut-off.

Thanks Jim- I searched the whole fuel system last year as I was suspicious before I ended up changing the pump. There is no in tank filter and no anti siphon valve. Tank and pickup screen were clean. Fuel filters are new. Haven’t closely inspected the lines but I’ll take a look.

It’s weird as I have never had an issue with vapor lock in the past, which makes me think it’s something else.

I’m going to pull the injectors some night this week and take a look and also check the fuel lines.

Anything else I should be looking for for my rough idle or lean condition?

[jlarkin.41]

The plugs that are light tan indicate a lean condition- they look normal for a car, but not for a boat.

Find a way to run diagnostics with a Tech 1 or something similar- doing it with a meter will just take too long and it will annoy you.

Vapor lock IS a possibility because the fuel pump is at the engine and not in the tank. Make sure the fuel line hasn't collapsed or de-laminated- it's getting close to 30 years old and ethanol isn't a good thing for that particular type of hose. Check for a fuel filter at the tank, too. If you find one and didn't know about it, I doubt it's allowing good fuel flow. While you're there, check the fuel pickup, check valve (if it has one) and the fuel shut-off.

Thanks Jim- I searched the whole fuel system last year as I was suspicious before I ended up changing the pump. There is no in tank filter and no anti siphon valve. Tank and pickup screen were clean. Fuel filters are new. Haven’t closely inspected the lines but I’ll take a look.

It’s weird as I have never had an issue with vapor lock in the past, which makes me think it’s something else.

I’m going to pull the injectors some night this week and take a look and also check the fuel lines.

Anything else I should be looking for for my rough idle or lean condition?

[mikeg205]

Also injectors may be not sending enough fuel in lean cylinders.

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[JimN]

Thanks Jim- I searched the whole fuel system last year as I was suspicious before I ended up changing the pump. There is no in tank filter and no anti siphon valve. Tank and pickup screen were clean. Fuel filters are new. Haven’t closely inspected the lines but I’ll take a look.

It’s weird as I have never had an issue with vapor lock in the past, which makes me think it’s something else.

I’m going to pull the injectors some night this week and take a look and also check the fuel lines.

Anything else I should be looking for for my rough idle or lean condition?

It may not be classic vapor lock, but it could be starved. Also, the fuel filter wouldn't be IN the tank, it would be ON the tank if it has a second one. The anti-siphon would be the piece that is attached to the outlet of the fuel shut off on the tank- looks like a regular barb fitting.

[jlarkin.41]

It may not be classic vapor lock, but it could be starved. Also, the fuel filter wouldn't be IN the tank, it would be ON the tank if it has a second one. The anti-siphon would be the piece that is attached to the outlet of the fuel shut off on the tank- looks like a regular barb fitting.

Thanks. I can confirm I only have two filters. One water separating between the tank and pump and one inline between the pump and injector rails. I took that barbed fitting apart next to the pet **** and it is just a barbed fitting with no check ball in it.

[jlarkin.41]

Also injectors may be not sending enough fuel in lean cylinders.

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Thinking the same thing. I have a ski buddy who works in a shop with a bench tester for injectors. I may try to get them checked on their flow rig.

[JimN]

Thanks. I can confirm I only have two filters. One water separating between the tank and pump and one inline between the pump and injector rails. I took that barbed fitting apart next to the pet **** and it is just a barbed fitting with no check ball in it.

I read the first page of comments and you wrote that the fuel pressure gauge wasn't on the engine when you have the stalling- it HAS TO be connected in order to perform a valid test because idle pressure is almost useless. You need the boat to be under load, on the water and the test is one at KEOE (Key On, Engine Off), idle, 2000 RPM and WOT, in gear. Y( ushould have a second person onboard to check the pressure and make notes, or you do that while they drive.

[jlarkin.41]

I read the first page of comments and you wrote that the fuel pressure gauge wasn't on the engine when you have the stalling- it HAS TO be connected in order to perform a valid test because idle pressure is almost useless. You need the boat to be under load, on the water and the test is one at KEOE (Key On, Engine Off), idle, 2000 RPM and WOT, in gear. Y( ushould have a second person onboard to check the pressure and make notes, or you do that while they drive.

I will do it again this weekend or some night this week if I get a chance and share the results but I did this last year while my wife was driving (after I started seeing issues). I dont recall the values, but it was in range with the values I found on this site at Idle, Under load and at WOT under load.

[mikeg205]

I will do it again this weekend or some night this week if I get a chance and share the results but I did this last year while my wife was driving (after I started seeing issues). I dont recall the values, but it was in range with the values I found on this site at Idle, Under load and at WOT under load.

Plugs show what is happening.. injectors need cleaning or replacement. Lots of fuel in some cylinders and barely any in others

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