1990 Mercury 2.5 L Won't Start

[douglaswood34]

1990 Franken motor
2.5 L Serial #OD007129
55 hours on rebuild

No issue with the block or those components. Started fine this morning. Went to change spots after about 2 hours and it plain would not start. It turns over fine. Battery is up to snuff and the terminals are clean. It would fire occasionally. That lead me to believe it was maybe fuel filter. I had old gas in the tank, less than 1/4. Filled her up to almost 3/4. It did have a slight miss yesterday and had issues getting up on pad. Went great of course once it got there. I changed the fuel filter/water separator and no change. Bulb was pumped up till hard on each attempt to start. The EFI pump was running per normal when the key was switched on. My plan of attack it to pull plugs in the morning to see if they are getting fuel first. Second check spark. Third I'll pull and reseat all the connectors to make sure it's not a bad connection. Since I'm on vacation I have very limited tools and didn't bring my manual. What else should I look for to start diagnosing this beast? I looked briefly for broken wires and found none.

[douglaswood34]

One more thing.... She has never seen ethanol gas since I had her rebuilt.

[douglaswood34]

No spark on 2, 4 ,6. Okay spark on 1, 3, 5.

[douglaswood34]

Okay. Next I removed the kill switch connection to the switch box on the outside. Fired right off and ran. Can I assume the kill switch is the culprit? Going to leave it off and test on the lake. If it performs I'll have to dig one of those up.

[rgsauger]

You can swap your switchboxes and see if the problem follows the box or not

[douglaswood34]

Good point. If she still doesn't run after trial today I will try that and do another spark test.

[EuropeanAM]

Save some time by simply repeating the spark test.

[douglaswood34]

It was more fun to get her on the water! She started okay. she is still a dog. Going to unhook the second switch box kill wire and see if it improves. Fairly certain it's related to the kill switch. Need to tear into all of the boxes from our move to find my manual and check all the outputs.

[EuropeanAM]

While you're in there- make sure you have a good White w/black stripe "jumper" between the two switch boxes (bias circuit jumper).

The black w/yellow stripe wires are indeed the kill circuit, but ALSO are used by the IGNITION SWITCH to kill the engine (same circuit used by both keyswitch and lanyard switch).

[douglaswood34]

Bias jumper is intact. Put the cut off wire back on and again she runs fine. I did work the lanyard switch a bunch. I think it is in fact corroded or just not in good shape. I will replace it.

[douglaswood34]

Okay. I have tested every part of the ignition system. All parts are within specifications listed in my service manual. Thought I didn't have spark on one side but that was incorrect. I was doing that test in brightsunlight and just couldn't see the spark I guess.

So onto the next step. Drain the tank and clean the entire fuel side. Other than the tank, where is the best place to start? The service manual doesn't outline a procedure so I guess just tear in and figure out if it's plugged someplace?

[JOE54]

getting fuel to vst ????? fuel psi test

[douglaswood34]

VST was full of fuel. Drained it, and checked the bottom. It was clear of gunk. Cleaned the needle with carb cleaner. Float appeared in good shape. Pulled the pulse fuel pump. Looked good except one of the smaller bolts is missing. Appeared to be sealing but I will replace that and get a diaphragm kit on order to rebuild. Inspected fuel lines under cowl and all appeared good inside and out. Going to go ahead and order a new bulb and line from the tank back to the pulse pump. I only have 53 hours on this since rebuild. The fuel injectors were serviced at that time. Next?

[douglaswood34]

This thing is a 1990 engine. Did they not have a schrader valve to check pressures? If not how do you properly check pressure?

[JOE54]

look down low on inj housing throttle cam area early ones where there

[douglaswood34]

Not sure how I missed the nice red cap! Now to find a test gauge to check.

[douglaswood34]

Any idea what size this schrader valve is so I can order the right adapter? I have one that would work, but it's too long and the shift/ throttle bracket is in the way. I need a 90 degree adapter. Any suggestions?

[EuropeanAM]

.302 x 32 if I recall correctly.

[douglaswood34]

Thank you very much.

[douglaswood34]

Okay. Still not 100% on what is going on so I went back to the basics. I did a compression test . 1,3,5 all at 130. 2,4,6 125, 135,130. That should be fine. Gapped all the plugs at .035". May try .040" tomorrow to see if I can get it to idle. All 6 coils throw a nice blue spark on a tester set at 7/16". All 6 plugs threw good spark. Fresh can (separate tank) of fuel mixed at 40:1 as recommended by Jay S. Pulse fuel pump rebuilt. Fuel lines check. Held the throttle down just a bit and she fired right off. Could not get her to idle down to where it was set, but just a smidge above. Revved okay but not too high, maybe up to 2000 rpms. It's sitting in a tank of water. Warmed her up to operating temperature. and shut her down. I should have the appropriate adapter tomorrow to measure fuel pressures. I am going to run some quickleen in her to see if that clears her up. I am thinking maybe the injectors are not perfectly clean. What am I missing? As stated above I have already went through the entire ignition system and everything including stator, trigger, cdi boxes and could checked out on specifications. One thing I have not noticed before though. When I turn the key on, the fuel pump runs as expected. Before I start it, if I leave the key on it will shut off. I don't recall that happening before but I could be wrong. Docent it run constantly but get throttled by the ECU? Anyway I'll know more tomorrow when I can check pressures.