Another 502 mag efi not starting. Tons of tests have been preformed.injectors fried?
 

Well guys here is another 502 mpi not starting issue. Just throw as many ideas out there as you can because I have fallowed Merc’s troubleshoot guide and tells me the engine should start, yet it dosen't. Wont even "pop"

Engine: 1994 Gen V 502 Mag EFI

Past info: Engine ran good last year.
----------------This passed off season, Fresh top end rebuild, and sent all the injectors out for flow testing and cleaning .

Symptom: Engine cranks & cranks & cranks with no start. After all my trouble shooting, (listed below in order I tested) I’m guessing some how all 8 injectors got fried at the cleaner.


Fresh 25 gallons of 91 octane, non oxygenated gas.

New fuel filter/ water separator.

Verified spark plug order to correct cylinder.

Verified correct firing order.

Pulled spark plug wire # 1 off spark plug and tested for spark. (good spark)

Check fuel rail that correct inlet and return lines are in correct spot according to Merc.

Swapped plug wires 180 degrees on distributor (to make sure my ignition is not 180 off).

Put plug wires back in correct order.

Verified spark plug order to correct cylinder again.

Doubled checked I didn’t miss a harness plug in and grounds.

Kill switch is NOT on. (When kill switch is on elec. Fuel pump won’t prime or turn on.)

Turn key on and fuel pump, pumps for 2 seconds.

Remove VST and check filter on electric fuel pump (good/clean), Tank full of gas.

Oil pressure switch is good since fuel pump turns on,

Took compression test. 150, 130, 130, 135, 125, 130, 130, 140, Good

Pulled wire harness off MAP sensor, (no change no start)

Put in jumper wire into DLC plug (put ECM in service mode). No start, no change.

All 3 fuses by ECM are good, and 12.8 volts coming into them..50 amp breaker good.

Had buddy spray carb cleaner into spark arrestor wile I start the engine.... engine STARTS!!, then dies when carb cleaner is no longer spraying. (umm Not getting fuel) (and timing must be pretty close to perfect)

All injectors are plugged in

Fuel pressure measured with Snap On gauge is 38 psi at rail.

Remove spark plugs, All plugs are still dry!!!????

Check ECM for voltage, J1-11 & J1-16 & J1-30= 12.8 volts, (good)
J1-30 & J1-14 to ground (good) .8 ohms. (ECM should have power then)

Bought Noid test kit for injectors, plugged into #8 injector harness (Easy to get to with out pulling intake) Pass!, Crank and light blinks showing it is getting impulse form ECM…

Troubleshooting as of last night: Conclusion = Fuel injectors are not opening. ECM is sending impulse yet there not responding. Some how they got fried when at the cleaner???

I’m sure I forgot a couple other things I did wile troubleshooting, but throw any ideas out there before I remove intake and swap injectors with a buddies set.

Rob.

what is the OHM reading across each injector? Did you pop the schrader valve and check for fuel? Did your remove the fuel lines from the rail? if so make sure you didn't reverse on installation.

No i didn't ohm out the injector or injectors yet. Once I Noid tested #7 last night, I shut down shop due to :poopoo:. It is on the list tonight to quickly check #7 for 12 ohm's +-.7 . To gain access to the others intake has to come off and I might as well swap injectors.

Yep, fuel gushes out and gets all over lower intake if you dont have a shop rag in hand ;) also it tested at 38 psi at rail

Yep, I did check them. They were reversed and now are in correct spot. Supply on bottom, return on top. PG: 5C-22 merc manual #17. The brown O-rings are a ***** to squeeze into the rail

Thank you for the ideas

An engine needs spark, fuel and oxygen. You say you have spark. Pull another plug or two and double up that verification. Next comes fuel & oxygen so the spark can create the internal explosion the cylinder needs for compression.

1. Re-verify you have spark (most issues are usually spark related)
2. Verify you have fuel (hear the low pressure pump pressuring up?) Put a fuel pressure gauge on the shrader valve to check key on.
3. Oxygen pretty takes care of itself coming in thru the intake.

^^^ Check. Yep. Thank you for the ideas.

Now here comes the "why the ***ing hell was it that" question?

Check resistance on injector. 11.7 ohms. perfect....

So i took a screw driver and tapped every injector several times. Said what the hell see what happens.. Started right up!!!!!!. Perfect idle = 700 rpm. Warmed up engine and brought revs up to 2,000. sounds perfect. What in the heck? Injector some how got stuck closed and needed a "tap".... Stopped engine 3-4 times and re-started with no problems.

At least it is working. Now onto another Question I need to search/ start a thread. I have less water flow on the starboard side exhaust!? I never noticed that before but then again I never looked or checked.

double post. opps

When I was in the Army we used to call that Percussion Maintenance-Glad to see you got it going again.

if by some chance you are in the market for injectors. i have 8 out of a 95 502 mag mpi. sonic cleaned and flow tested by witchunter performance. rebuilt my 502 with a procharger and aluminum heads to find out on the dyno stock injectors were not big enough. so had to get bigger aftermarket ones. if intrested let me know.

More than likely they still had some test fluid in them, which is not flammable. I have seen this when winterizing with too much Marvel Mystery oil. It basically just sits in the injector and barely oozes out during cranking, until enough of it is displaced by gas, no startee.

Greg: Well I dont "need" any injectors now that mine have just been cleaned and now working. But depending on the price you want to sell them for I wouldn't mind having a extra set around for the "just in case" or maybe have a cleaned set waiting for Maintenance reasons. PM me.

Ted: Yep, that must have been it. Well at least now we/I know and maybe it will help some one in the future, when searching a non starting mpi engine.