5.7LX EFI low compression - need advice

[hnt]

Okay so I spent all day Friday putting the engine back together. New head gasket, valves adjusted, new water pump impeller, new thermostat, manifolds and risers checked for true and clean mating surfaces. Reassbled everything with new FelPro gaskets (except for OEM riser gaskets) and carefully torqued to spec. I also reinstalled the distributor to the mark for #1 cylinder.

When I tried to start it this am it turned over but would not start. I was getting spark but I don't think I am getting fuel. I had to leave so wasn't able to do much troubleshooting. The engine is a 1996 5.7LX Efi 250 hp non-vortec It has a mechanical fuel pump, a VST and a throttle body. When I removed the VST I lost some gas out of it. Does the fuel system need bleeding?

I understand that a Mercruiser scan tool must be used to set the base timing on this engine and you cannot connect a purple/white wire to ground and use a standard timing light as on some models. If that is the case I will need to have the service department do that and I will have them check why its not starting too. They are still very behind and it will be "a while" before they can look at it and summer is marching on :facepalm:.

In the meantime does anyone have suggestions for troubleshooting?

Thanks

 

[Bt Doctur]

you cant have a mechanical fuel pump with TBI or EFI systems

 

[tpenfield]

you cant have a mechanical fuel pump with TBI or EFI systems

I have the mechanical fuel pump that runs off of the sea water pump on my engines Mercruiser 7.4 LX MPI . . .

 

[stonyloam]

Make sure that you did not install the distributor 180 degrees out. It needs to be on #1 compression stroke.

 

[nateo]

Sound s more like timing/distributor install issue then fuel. See the following thread for finding tdc on compression. http://forums.iboats.com/forum/engi...7-how-to-find-1-tdc-on-the-compression-stroke

Then rotor needs to face #1 spark plug wire. Double check all wires going to correct cylinder. Why doesnt timing light work? Computerized somehow or something? On my thunderbolt iv i dont have to ground anything. What ignition do you have?

 

[nateo]

I put all my stuff in my signature, it helps the wizards help me

 

[hnt]

Hi Thanks for the responses,

I do have a mechanical fuel pump in my system. Engine is a 1996 5.7LX EFI Model #4-57L111JS, s/n 0F761024

Also I am sure I have the distributor installed correctly. I found TDC on #1 and marked the distributor and the manifold before removing it to replace the head gasket. I did not turn the engine at all before reinstalling the distributor in the same direction.

I have attached a wiring diagram below showing the system I have along with the timing instructions I found in Service Manual 17

Thanks

 

[hnt]

I spoke to the mechanic this am and he thinks I probably have air in the fuel system. (He also raised the question about the distributor being installed correctly) I did not see any evidence of fuel coming out of the injectors in the throttle body when I tried to start it over the weekend. I hope to get back to the boat Friday afternoon to see if I can do some more fuel system troubleshooting.

My hope is that I will be able get it running so I can get the mechanic for a few minutes to set the base timing.

 

[nateo]

your thread hasn't indicated if you found tdc on compression stroke. It's possible for #1 to be at tdc on compression or intake stroke.

 

[hnt]

Good morning,

I have an update.

The mechanic at the marina has finally been able to take a look at my engine. We are definitely dealing with a fuel issue. He confirmed we are getting spark and was able to get it to fire by spraying fuel in the throttle body. The injectors are not firing and we are not getting power to them. Fuel pressure is good. The diagnostic scan tool does not register any RPM when cranking and therefore the computer is not sending voltage to the injectors. The troubleshooting will continue today but it seems we are getting closer.

I will report the final outcome.

Thanks again for everyone's help

 

[hnt]

Good morning again,

Problem solved!

The reason it would not start is totally on me. I had two of the electrical quick connections crossed upon reassembly. Apparently In 1996 for part of the model year Mercruiser used the same electrical plug on two components on the wiring harness. Anyway it took a little while to find the problem but once they did the injectors started working and it fired right up. They set the base timing and did a sea trial and it ran great.

I really appreciate all the good advice in helping me through this.