Mercruiser Twin 8.1Ltr's EFI - Need Help !!

[kfraser65]

It's sort of a long story, but I wanted to get all the info out there in hopes that someone might be able to help me. I bought this boat from an insurance auction. The boat had broken loose from it mooring and took on water and was submerged in about five feet of salt water for about 4 hours. The motors were drained and preserved. I have both motors free and turning. Both have 125 lbs of compression on all cylinders. All cylinders are getting fire from the coils. I have 45 lbs of fuel pressure @ the rails, and all injectors are firing. One of the PCM's was DOA, so I replaced that one. Here is what I get. Neither engine will start. They both turn over, but will only back fire through the throttle body. I hooked up the Rinda Tech Mate scan tool and am getting no bad codes on the port or starboard engine. ( Bad code for Speedo tube, but nothing that would prevent starting). Crank, Cam & Throttle position sensors are all good. I removed the valve covers and have no stuck valves. I am down to my whit's end???

Engine Ser # OM9XMO8

 

[harleyman1975]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

The 8.1 in my truck uses a mass airflow sensor. I don't see one in your pic. Not too familiar with the marinized version of this motor but I am suspect of the ignition system...just a gut instinct though.

 

[kfraser65]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

At this point, I'll throw anything out there. I had someone tell me the cranking amps on the batteries I'm using are too low. I checked and the recommended MCA should be 800. Mine are 585 MCA. Could this cause both motors to not start and just back fire once though the throttle body?

Thanks Everybody !

 

[Fun Times]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

One of the PCM's was DOA, so I replaced that one. Crank, sensors are all good.

Engine Ser # OM9XMO8

Hi there, Did you buy a new or used PCM? Was it the same part numbers?

Also you serial number is invalid due to there are letters where there should be numbers in place. A partial serial number will only yield less accurate information at times.

I have seen many times people say the crank sensor checks out good when in all actuality it was a bad crank sensor in one way shape or form. And since it was under salt water it could still be the case. The crank sensors are sensitive to many things including any type of contamination build up as the sensor is designed to contact the reluctor wheel of the crankshaft. Below is a very helpful manual for the 8.1 crankshaft sensor if you read its entirety.

2002 8.1l V8 Crankshaft Position Sensor - Silverado & Sierra 1500 - GM-Trucks.com
The reason i remembered the manul above,
http://forums.iboats.com/mercruiser...-but-will-not-spark-no-rpm-diacom-590452.html

I checked and the recommended MCA should be 800. Mine are 585 MCA. Could this cause both motors to not start and just back fire once though the throttle body?

Thanks Everybody !

Yes it could as you don't have enough power to power up all the circuits while cranking over the engine.

You would be much better off with having as close to 1000 CCA / 800+ MCA.

Good luck.

 

[kfraser65]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

Wow, Did I ever mess up the Ser#.. It should be OM316113. The PCM was purchased used. It was exact part number. The issue I'm having is exactly the same on both engines. I'll try a new battery and check the Crank & Cam sensors. Any other suggestions would be appreciated... Thanks Again !

KevinF

 

[kfraser65]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

After a long and frustrating journey, I have solved the issue with both engines not starting and only backfiring through the throttle body. I've got $25 bucks sitting in a pay-pal account that I will give away, if anyone in the first 20 responses get's it right. I can tell you it was not a battery issue, nothing to do with the PCM, crank or cam sensors, throttle sensors, or any sensor for that matter, nor was it anything to do with the ignition system. Put on your thinking caps folks !

Kevin

 

[Bondo]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

After a long and frustrating journey, I have solved the issue with both engines not starting and only backfiring through the throttle body. I've got $25 bucks sitting in a pay-pal account that I will give away, if anyone in the first 20 responses get's it right. I can tell you it was not a battery issue, nothing to do with the PCM, crank or cam sensors, throttle sensors, or any sensor for that matter, nor was it anything to do with the ignition system. Put on your thinking caps folks !

Kevin

Ayuh,.... Ya found out Water does pressurize in the rail, but Don't burn so well,......

 

[alldodge]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

It's a fuel issue

 

[Bondo]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

Today, 03:40 PM

Today, 03:42 PM

Ayuh,.... You type s l o w e r than my single digit,.......... :laugh:

 

[alldodge]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

Today, 03:40 PM

Today, 03:42 PM

Ayuh,.... You type s l o w e r than my single digit,.......... :laugh:

Yep I'm a hunt and pic-kinda guy and probably talk to much on the computer any way.

:laugh:

 

[dingdongs]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

put wrong starter on opposite engine.

 

[bspeth]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

off topic: she looks like the ss minnow.

 

[kfraser65]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

bspeth.... Not even close...

 

[LorenHaus]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

Electrical or mechanical problem?

 

[haulnazz15]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

Well I was thinking maybe the kill switch at the helm was engaged, but that's sorta the same as the ignition system.

 

[OllieC]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

I'll bet the canvas on the fly bridge had something to do with it......

 

[500dollar744ti]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

Was the gas tank full of water?

 

[Walt T]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

Nut behind the wheel

 

[kfraser65]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

The engines were preserved within a couple of hours of her taking on water. Before I bought the boat, the marina in Key Largo replaced both starters, changed all of the filters, drained all the fluids, & fogged the cylinders. I wish someone had told them that both of these engines are CCW ROTATION !! They replaced both starters with CW rotation...! I never took the starters off and didn't even think to check the rotation...lol. Two new starters and both engines started right up!

 

[500dollar744ti]

Re: Mercruiser Twin 8.1Ltr's EFI - Need Help !!

That's weird, someone did guess relatively close to that..

Why would they both be CCW?