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1994 502 EFI Raw Fuel From Exhaust

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1994 502 EFI Raw Fuel From Exhaust

Old 07-09-2015, 09:01 PM
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Default 1994 502 EFI Raw Fuel From Exhaust

I have a pair of stock 1994 502 EFI's. Total hours: 532. Hours on engines since rebuild: 80. I've had some issues with these motors in the past. All seemed to be fuel related. Evil VST's. I blamed everything bad that ever happened to me (on and off the boat) on the Fn VST's. So this winter's project was to remove the VST's and go Aeromotive. Eddie Young did the fuel rails for me. Opened up #7 and set them up to feed from both ends. After 10 micron filter, AN10 split to two AN6 feeding the rail. AN6 out of the rail to Aeromotive regulator. From Regulator 3/8 return line to the tank via fill hose bung. Regulators are set at 37psi and drop to about 33-34psi idling. All Injectors were sent out to be cleaned and flow tested.

Port motor starts, idles, and runs flawlessly. If it wasn't for the gas slick behind me along with the smell of gasoline I would never suspect anything was wrong.

Next step was to look at distributor cap and rotor. My Ah-Ha moment. Pulled the wires off and the post for #2 had carbon on it. Put the wire back on and sure enough it was loose. So new cap, rotor, wires, and plugs and I know I've got this fixed- Nope. Fire it up and within 2 to 5 seconds I'm doing my best BP impression.

Now I'm thinking it must be MAP sensor. I have a parts donor sitting right there so I swap MAP sensors. Fire the motor up (again cold) and you guessed it- no change. Fire up Starboard side and no gas slick.

Ran about an hour and pulled the plugs. All are dark brown to black.

I got a hold of a scan tool today and here are the numbers:

Coolant Temp 154F (New Mercruiser 160 T'stats just installed)
Map Volts 3.27
Manifold Pressure 21.4
Baro Volts 4.93
IAC Position 82
Base IAC position 80
Injector On Time 3.8
Injector On Time Crnk 9.6
Fuel Flow Rate 2.1

These readings were taken immediately after a ten minute run at 4200rpm. Then did a quick WOT run with both motors hitting 5200rpm and temp on scanner dropped to 151.

Suggestions on what to try next?

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Old 07-10-2015, 08:49 AM
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Give Eddie a call, he surely will have some pointers related to these mods.
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Old 07-10-2015, 09:32 AM
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Do you have scan readings at idle or it was taken at idle after a 4200 rpm run. Not sure about what rpms your scan was done.

Last edited by BUP; 07-10-2015 at 09:49 AM.
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Old 07-10-2015, 02:26 PM
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Scan was done at idle after the run. So it sounds like my MAP voltage is too high which in turn is firing the injectors too long. New Map going on tomorrow and I will report back with what I find.

Thank you.
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Old 07-10-2015, 03:49 PM
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yes sir posted this back a few days ago then seen you reposted again. anyways my take on from the your first post. Just was not 100 % sure about what rpms your scan was taken, that's it.

Link below.

http://www.offshoreonly.com/forums/d...g-exhaust.html
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Old 07-11-2015, 02:44 PM
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New MAP sensor installed- little or no change. MAP volts did drop to around 2.8 but not below that. As I advance the throttle the MAP volts goes down. I would expect it to go up as throttle is increased because manifold pressure should increase. At 3000 RPM (TPS Volts 0.99) MAP volts drops to 2.03. This holds true with 3 different MAP sensors.
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Old 07-12-2015, 12:44 PM
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I would say then You have a stuck float in your VST flooding the VST into the engine - but you do not have a VST CORRECT ? So that would NOT be the problem. So rule that out

Is your new T stat sealing in the housing as they have that round cork gasket that many miss replacing with new to seal the t stat internally against the housing . Clean that area and dig out the old one then replace with the new one.. 154 degrees from the coolant temp reading on the scan from a 100 % fully warmed up engine after hard runs and dropping at WOT ?

Also for the t stat housing itself to seal against the intake - does your t stat housing use the 4 tiny rivets in the gasket and if so did you put sealant on it. If so that is the wrong way to install that gasket to the t stat housing. Those tiny rivets in the gasket are for grounding the t stat housing and can effect the temp readings plus screw up the warning horn for its ground . .

Next questions - what is your fuel pressure and when you shut off your engine does fuel pressure hold ? If it drops right away - you have a or stuck open injector(s) or possible a fuel pressure regulator .problem.

what rpms does your engine run at idle speed and does the idle rpms jump around a lot.
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Old 07-13-2015, 09:02 PM
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Thank you BUP. I am familiar with the gaskets on the t-stat housings. I did r&r the cork gasket inside and didn't use any sealant between the block and the housing. After assembly I even tested continuity between both temp senders (gauge and ECM) and the block. Both had good ground. I will probably open it back up and see something didn't possible move during assembly.

Back to the fuel problem. Compression test shows #7 low, about 95psi cold. Put some oil in the cylinder and repeated compression test still didn't hit 100psi. Now I'm thinking valve or possible valve issue. I question the fact that #7 plug looks better than the other three on that side? Maybe exhaust valve? Could it be blowing the raw fuel out before it gets a chance to burn it?

Next step is to pull it apart and see what it find.

Again thank you for your help and I will report back with what I find.
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