HELP Gen lV Mercruiser 454 EFI VST issues

[norcalLmo]

I have a stock Gen lV Mercruiser EFI with VST issues - It runs fine, however there is raw fuel coming out of the starboard exhaust (23' Warlock with stock Mercruiser risers and thru transom exhaust) a local shop suggested it's my VST. These things are almost non-existent -(ebay, craigs, local shops etc) Any recommendations for either repairing or replacing this design?? Some posts recommend the Aeromotive 1000a fuel pump, regulator and filter - Has anyone here done this conversion and if so pics would be GREATLY appreciated
Thanks!!!

 

[Trash]

I have a stock Gen lV Mercruiser EFI with VST issues - It runs fine, however there is raw fuel coming out of the starboard exhaust (23' Warlock with stock Mercruiser risers and thru transom exhaust) a local shop suggested it's my VST. These things are almost non-existent -(ebay, craigs, local shops etc) Any recommendations for either repairing or replacing this design?? Some posts recommend the Aeromotive 1000a fuel pump, regulator and filter - Has anyone here done this conversion and if so pics would be GREATLY appreciated
Thanks!!!

You could have one of the internal diaphragms of the VST that has failed. When this diaphragm fails it ports fuel into the intake manifold via a yellowish colored tube from the top side of the VST system. There are parts available to repair the system, they just aren't always cheap.

Another likely issue is you have an injector hung open and it's draining fuel into the cylinder. Actually this is more likely the issue the more I think about it. Check your oil for dilution or gas fumes.

 

[Duck'ed_Up]

Just had the same problem. Buy a VST O-ring rebuild kit and a diaphragm kit. You must drain the oil because it's very likely it was dumping so much fuel it was passing the rings thus making oil. Pull the dipstick you will smell the fuel in the oil. It's about 1hr and a 1/2 fix. Just be careful with the screws that hold the pump to the tank... they strip easy.

 

[norcalLmo]

Thanks for the quick response guys!!!

Trash - any recommendations on how to determine which injector(s) are hung up (since both problems seem to dump raw fuel into the oil)?

Ducked - can you provide part #'s and where you got your o-rings/gaskets?

Thanks again guys - always a wealth of knowledge on this forum!!!:thumbsup

 

[Fun Times]

A stuck float or ruptured diaphragm inside the VST is the most likely cause as it's sort of common and a good place to start.

Using a screwdriver impact driver helps break the top screws loose and is the least likely way to strip the screws out so quickly/easily as long as you have a "really" good fitting screwdriver bit before trying to actually remove them. Afterwards I put in Allen head screws with a light coat of Permatex Thread Lock And Sealant so it's easier the next time I need to be inside there.

Be sure to carefully clean the Screen while you have the VST apart as that filter is crazy expensive at $480.47. Item number 9 seen below.
What is your engine serial number? Be sure to match your serial number within the range of one of the links below for parts and numbers,
http://www.mercruiserparts.com/bam/subassembly/31796/1614/160
http://www.mercruiserparts.com/bam/subassembly/31796/1614/170

While not listed in the parts catalogs linked above, Merc part number 25-803831 is the O-ring for the top cover of the Vapor Separator Tank on older fuel injected MerCruiser engines which is now available separately. You do not have to order a complete Top Cover Kit or O-Ring Kit when changing/cleaning the filter or checking the float setting. But bear in mind that this O-Ring does comes in/with as a kit should you order either item number 5 or 11 for a rebuild job.

You may just need the top O-ring and item number 6 to start while item numbers 3 and 4 maybe.

 

[Trash]

A stuck float or ruptured diaphragm inside the VST is the most likely cause as it's sort of common and a good place to start.

Using a screwdriver impact driver helps break the top screws loose and is the least likely way to strip the screws out so quickly/easily as long as you have a "really" good fitting screwdriver bit before trying to actually remove them. Afterwards I put in Allen head screws with a light coat of Permatex Thread Lock And Sealant so it's easier the next time I need to be inside there.

Be sure to carefully clean the Screen while you have the VST apart as that filter is crazy expensive at $480.47. Item number 9 seen below.
What is your engine serial number? Be sure to match your serial number within the range of one of the links below for parts and numbers,
http://www.mercruiserparts.com/bam/subassembly/31796/1614/160
http://www.mercruiserparts.com/bam/subassembly/31796/1614/170

While not listed in the parts catalogs linked above, Merc part number 25-803831 is the O-ring for the top cover of the Vapor Separator Tank on older fuel injected MerCruiser engines which is now available separately. You do not have to order a complete Top Cover Kit or O-Ring Kit when changing/cleaning the filter or checking the float setting. But bear in mind that this O-Ring does comes in/with as a kit should you order either item number 5 or 11 for a rebuild job.

You may just need the top O-ring and item number 6 to start while item numbers 3 and 4 maybe.

Perfectly stated. I can't emphasize enough about a good fitting screwdriver bit on the cover screws. I was fortunate to have all of them break loose cleanly.

 

[Trash]

Thanks for the quick response guys!!!

Trash - any recommendations on how to determine which injector(s) are hung up (since both problems seem to dump raw fuel into the oil)?

Ducked - can you provide part #'s and where you got your o-rings/gaskets?

Thanks again guys - always a wealth of knowledge on this forum!!!:thumbsup

I'd start with pulling the plugs one at a time after the motor has sat for a while. The culprit cylinder will likely be wet or wreak of gas. There might be more eloquent methods but I'm not super sharp on the best test. It might be worth while to have the injectors cleaned and tested too.

 

[norcalLmo]

You guys ROCK!!!! I'll get to work and keep ya'lls posted Huge THX for your quick response and recommendations! Be Safe!!

 

[Trash]

Let us know the results as it will benefit all parties involved. Best of luck.

 

[SBMech]

I'd start with pulling the plugs one at a time after the motor has sat for a while. The culprit cylinder will likely be wet or reek of gas. There might be more eloquent methods but I'm not super sharp on the best test. It might be worth while to have the injectors cleaned and tested too.

Fixed that for ya

Plug would be wet as well, and dark compared to the rest.

IF it was a stuck injector, you would have a solid misfire and uneven engine running.

 

[norcalLmo]

Thx for the update SBMech - I haven't had a chance to pull the plugs yet - the motor ran smooth with no back/misfire - no idle issues - so with that I'm still going to pull the plugs and inspect them, but I'm leaning more toward a stuck float in the VST tank. I'll update this post as soon as I get some more info - thanks again gang!!

 

[Trash]

Thx for the update SBMech - I haven't had a chance to pull the plugs yet - the motor ran smooth with no back/misfire - no idle issues - so with that I'm still going to pull the plugs and inspect them, but I'm leaning more toward a stuck float in the VST tank. I'll update this post as soon as I get some more info - thanks again gang!!

Do you have any hard starting issues after a period of run time, akin to vapor lock? The reason I ask is that the internal float or diaphragm problems can appear to be vapor lock when in fact its merely flooding the engine after shutdown. Basically look for liquid in the yellow tubing running from the VST and if present you have a diaphragm problem.

 

[norcalLmo]

Quick Update -
It's been like 'Satan's-Butthole' hot here in Sacramento so really didn't have time/energy to 'dink' with it until last night at 9:30 LOL! Pulled the plugs on the Starboard side - wet/soaked with raw fuel on #8? Pulled the top off the VST and checked the float, filter screen (clean) and VST top o-ring - all appears to be fine (*I don't know what the heck to look for, but nothing looked 'jacked-up' LOL! Re-installed the top - replaced plugs - test ran it - SAME FRIGGIN THING - RAW FUEL DUMPING INTO THE STARBOARD EXHAUST! (neighbors really appreciated the straight exhaust and me cussing at 10PM LOL!!!!

So after a Jack n Coke, shower and little more research on the another forum Off********.com Search: Raw fuel on Starboard exhaust - There's an amazing thread of the exact symptom, pictures and solution: Wait for it>>>>>>>>>>>>>>

VST Diaphram kit # 808509 - Classic symptom to-the-T!!!

Ordered a new kit and should be here early next week and I'll update - again!

Just to answer some the questions asked -
1. no rough idle or back-fire
2. no leaks from the top-VST tank o-ring
3. filter appeared to be clean - no tears or laquered gas residue
4. the rear two plugs on Starboard side were soaked * may still have an injector issue if after the diaphram replacement doesnt resolve raw fuel issue
5. no difficulty start-up or Vapor lock issues
6. I've run the motor about 10 minutes total with this issue - no INCREASE in oil level and existing oil does not smell like fuel so HOPEFULLY not an injector + VST combo issue - but I'm replacing the oil just in case

I'm not savvy on the whole cut n paste or computer linking of articles, however the forum discussion referenced above has some SOLID details & pics for this problem

Thanks again gang - I'll keep ya'lls posted:thumbsup

 

[Trash]

Quick Update -
It's been like 'Satan's-Butthole' hot here in Sacramento so really didn't have time/energy to 'dink' with it until last night at 9:30 LOL! Pulled the plugs on the Starboard side - wet/soaked with raw fuel on #8? Pulled the top off the VST and checked the float, filter screen (clean) and VST top o-ring - all appears to be fine (*I don't know what the heck to look for, but nothing looked 'jacked-up' LOL! Re-installed the top - replaced plugs - test ran it - SAME FRIGGIN THING - RAW FUEL DUMPING INTO THE STARBOARD EXHAUST! (neighbors really appreciated the straight exhaust and me cussing at 10PM LOL!!!!

So after a Jack n Coke, shower and little more research on the another forum Off********.com Search: Raw fuel on Starboard exhaust - There's an amazing thread of the exact symptom, pictures and solution: Wait for it>>>>>>>>>>>>>>

VST Diaphram kit # 808509 - Classic symptom to-the-T!!!


Ordered a new kit and should be here early next week and I'll update - again!

Just to answer some the questions asked -
1. no rough idle or back-fire
2. no leaks from the top-VST tank o-ring
3. filter appeared to be clean - no tears or laquered gas residue
4. the rear two plugs on Starboard side were soaked * may still have an injector issue if after the diaphram replacement doesnt resolve raw fuel issue
5. no difficulty start-up or Vapor lock issues
6. I've run the motor about 10 minutes total with this issue - no INCREASE in oil level and existing oil does not smell like fuel so HOPEFULLY not an injector + VST combo issue - but I'm replacing the oil just in case

I'm not savvy on the whole cut n paste or computer linking of articles, however the forum discussion referenced above has some SOLID details & pics for this problem

Thanks again gang - I'll keep ya'lls posted:thumbsup

That is the exact part I referenced in my first response. However.....you can't see the failed diaphragm unless you take the VST top off, flip it over and there are three screws that hold a small plate in place. Beneath that is the suspect diaphragm.

And on the big blocks it vents directly into #8. Small blocks in back side of the TB and front of the Scorpion bread box manifold.

 

[norcalLmo]

Yup Yup - the float assembly is held by a single screw - do I need to remove this to access the 3-screws holding the diaphram in place or can I leave it in place - I'm just a little worried about the float spring and plunger?

 

[Trash]

Yup Yup - the float assembly is held by a single screw - do I need to remove this to access the 3-screws holding the diaphram in place or can I leave it in place - I'm just a little worried about the float spring and plunger?

It's been a year or so since I did mine so I apologize for the hazy description. I believe I did remove the float and plunger to access the cover plate. There were 2 or 3 stainless screws holding the cover plate in place. Beneath that is the diaphragm that is likely crumbling apart. I wish I had taken pictures but I didn't.

Beneath the cover plate is a spring and the diaphragm. Make sure to document / remember the orientation of the spring in reference to the cap and diaphragm. Take pictures. It can go in wrong (the spring that is).

 

[norcalLmo]

Just got the diaphram kit - It's like Christmas, but in July LOL!!!!! Hope to get some time to 'fiddle' with this project this weekend and I'll update
No Worries Trash - I appreciate the continued info - every bit helps

 

[Duck'ed_Up]

Just got the diaphram kit - It's like Christmas, but in July LOL!!!!! Hope to get some time to 'fiddle' with this project this weekend and I'll update
No Worries Trash - I appreciate the continued info - every bit helps

This will fix your problem!

 

[mstanaszak]

Was there any resolution to this issue? Was the problem fixed?
I’m having the same issues and have already had the injectors cleaned.