MERCURY LASER EFI - What's the bare minimum needed to run?

**Smalltownbassin** · 11-22-2022, 08:21 AM

Wrapping up a carb to EFI conversion and just curious what all can be deleted from a stock 2.5L laser EFI setup and still function? Im still running a stock black ecu for now so i expect most of the supporting crap to be needed but hoping i can get away with nothing but a fuel pump, plenum w/injectors and ecu.

**OnPad** · 11-22-2022, 08:45 AM

To work right you'll need a fuel regulator, tps, map, and temp sensor.

**Smalltownbassin** · 11-22-2022, 08:56 AM

I've got all that in the Plenum. That it?

**OnPad** · 11-22-2022, 09:05 AM

That's all I can think of at the moment. You will also ground one wire from ecu, that went to a timing module if you have them removed.

**rjdubiel** · 11-22-2022, 09:30 AM

https://www.google.com/search?q=VST+...hrome&ie=UTF-8

here is a google search for VST Tank delete. Lots of threads on what you are looking to do.

A little note on searching. I use google, I type in what I am looking to find and then put this behind it: "screamandfly.com"

this searches key words just from S&F and is much better way to find info.

**DOC W** · 11-22-2022, 10:09 AM

you will need the three wire temp sensor in the head also . air temp sensor , tps, head temp, ignition power supply to efi harness purple wire, you can mount pump in boat and run just a regulator on motor

**PanRonnie** · 11-22-2022, 01:50 PM

You want to put an extra ground wire from the ecu body bare aluminium to the engine block! This is usually done at the top of the mounting rubber there is a service bulletin about this making sure there is enough ground for the injectors through the ecu

**Smalltownbassin** · 11-22-2022, 08:30 PM

Thanks guys. I think ive almost got it. Hooked up an old 150 ecu just to see if everything was talking the same language and she popped off pretty good. Put it on muffs and the idle is decent for being so lean. But i wanted to try checking the TPS and i cant seem to make it effect anything. Is there an ohm scale to check one vs. using the oem adapter to check voltage per the manual?

**OnPad** · 11-22-2022, 09:10 PM

I believe it to be more accurate using the volt method, with a test lead adapter. Or you can put some thin wire in your plug and create your own pigtail. Has to be plugged in, ignition on, head temp unhooked. .135v+/- at idle, 7.46v at full throttle. Voltage should increase and decrease smoothly when you move throttle arm.

**PanRonnie** · 11-22-2022, 10:08 PM

For the newer 824003 the idle voltage should be higher
Also disconnect headtemp sensor when setting the voltage
And you want to make sure your ecu matches the vst unless you use an adjustable fuel regulator
The fuel pressures differ from external pump to intergrated pump could cause a lean issue

**OnPad** · 11-22-2022, 10:16 PM

Thanks, Ronnie. I just grabbed the first service manual on the shelf. Was a old one.

**Smalltownbassin** · 11-23-2022, 07:09 AM

Well that may explain why the tps isn't effecting mixture. This old 150 ecu came off an old black vst laser setup. I'm running the newer, unpainted style. Got a friend bringing a 200PM ecu for a test piece today. We will see what happens.

**Smalltownbassin** · 11-23-2022, 08:23 AM

Alright so i cut a few loose strands of wire to extend the plug connections for voltage readings. Since the manual references using the test harness it doesnt specify which wire is measured against which. The lowest voltage my tps can seem to reach is about 1.5vdc. It maxes out at 7.68vdc. If i check the other wire i get the same but opposite. It starts high and goes low. Which wires should i be reading for idle and wot?

**PanRonnie** · 11-24-2022, 06:27 AM

Plz ignore the voice! Its horrible blame chaz for making me do this

You need to loosen the screws and adjust the tps

**Smalltownbassin** · 11-25-2022, 07:23 AM

After some tweaking with the TPS, butterfly idle position (top set open about 1/32nd), and bypassing the pump driver on the 200PM ecu i think we have a baseline to do some water testing and plug reads. This thing literally jumps to attention if you bump the key. No lean sneeze. No coughing. Lots of blue smoke with very little unburned fuel smell. All six plugs are wet. Ill let yall know how it turns out. Frankenbeast is getting the squirt now it appears lol! Oh yeah, after melting down #4 from that old ignition issue, i was able to fix the cylinder by going from 15 to 20 over. She is good as new with new rings, bearings, rod bolts and seals. 120psi on all 6 and not even begun break in. Hopefully i dont take her out again with shotty efi components lol! We shall see.