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Issue with Rebuilt 5.7L EFI Mercruiser

C

curlew97

New member
Greetings

I have a bit of an issue that has me stumped ... I rebuilt both of my twin 1997 5.7L EFI - TBI Mercruisers over the winter. One engine runs like a dream. The other not so much ... I am having an issue with the EFI injecting way too much fuel which has led to plug fouling, black smoke in exhaust with a gas smell and a loss of power under load. Other engine has no issues at all. I have listed the items that I have replaced thinking that it was a fuel pressure or sensor issue messing with the ECM. I have swapped parts from the good running engine to troubleshoot. I have noted those items below. I am at a loss here since I figured both engines would be running well after the rebuilds.

Compression has been checked all cylinders 175PSI +/- 3PSI
Valve Lash adjustment re-checked


Any help is appreciated. Thanks!

Will


Components Replaced with new

fuel pressure regulator
throttle position sensor
map sensor
distributor cap/rotor
spark plugs
engine coolant temp sensor

Components swapped from good engine

Distributor
Ignition Coil
ECM
 
So, whatever the problem is told the different TBI to inject too much fuel? That makes me think that the issue is not that it is getting to much fuel but it's not getting enough air. What is the vacuum at idle on both engines?

Does the ECM control the amount of fuel delivered?
Click to expand...
Yes...based upon the different inputs it receives from the various sensors. You have replaced/swapped nearly everything that tells the ECM what the engine is doing.
 
guyjg said:
So, whatever the problem is told the different TBI to inject too much fuel? That makes me think that the issue is not that it is getting to much fuel but it's not getting enough air. What is the vacuum at idle on both engines?

Yes...based upon the different inputs it receives from the various sensors. You have replaced/swapped nearly everything that tells the ECM what the engine is doing.
Click to expand...


I will be down at the boat on Saturday and check the vacuum. I am hoping it is something that i have overlooked. I am not sure if bad gas would cause this or a bad fuel hose. Would a cracked intake manifold affect the fuel delivery if the MAP sensor was reading more air coming in and then adjusting the fuel accordingly?

Thanks ... Will
 
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