1998 7.4 MPI No Start, Good spark, no fuel dun dun dun....

So i am hoping someone on here may be able to help me out. I bought a 1998 mercruiser 7.4L mpi a few months ago and decided to spend the next few weekends getting it running. Dash hour meter has <100hrs on it. Oil was clean, not milky or watery so i figured it was worth the risk.

First things first:
Mercruiser 7.4L (L29) MPI w/ bravo one
Engine Serial number is 0L335345
MEFI3
Delco EST igintion


I knew it was going to be a fixer-uper but i got her for a steal (or atleast i thought i did). I knew right off the bat i would need to change impeller, fuel filter and pump (previous owner said it was run dry and burnt up), spark plugs, fuel lines, risers, bla-blah-bla..

My problem is that the motor will not start. Here's what i have checked (and my thinking behind checking it):

1. Air - Intake is clear. Wont even sneeze or act like it wants to fire.

2. Spark - so i checked the number 1 spark plug and i have an orange spark. Spark plugs were old and a little fouled (good color thought) so i put in NGK BPR6EFS, and verified that the plugs were in the correct firing order on the distributor cap. checked the resistance of the coil and spark plug wires, and everything was within tolerances in the manual so i didn't change out the coil or wires. no tracking on the distributor cap either. After i put the new plugs in i bought a cheap spark plug tester and tested all the plugs and coil output- all good there.

3. Fuel - Here we go... First of all i replaced the fuel pump (and filter) because it was run dry and burned up. I didn't have a fuel pressure gauge in my arsenal so i rented one from autozone and it was missing a needle piece to depress schrader valve on the fuel rail. But i know i have a good bit of pressure, because when i press the schrader valve in with a screwdriver it shoots across the room. So since i have fuel in the rail i moved on to the injectors. Being that i just put in new plugs and turned the engine over several times i decided to pull a plug and do the old sniff test for fuel. Not even a hint of gas. Then i started getting desperate and i took of the plenum and checked out the cylinders and injectors. Bone dry. Every last cylinder. (Re)Checked fuses and power going to injectors. Voltage on the little pink wire (and pnk/wht wire) where it should be. So then i did what any country boy would do. Sprayed each cylinder with a shot of starter fluid and buttoned her back up. Sure enough she fired right up, of course only for a moment until she burned off the starter fluid.

Got to reading forums and the manual and trying to make sense of what i have. I disconnected the TPS and still no dice (thinking maybe it was just in clear flood mode). Made a homemade DLC code reader with an LED and paper clip and no codes were thrown (well except 12 which i think means all is well). Also read somewhere that there is a coil in the distributor cap that sends pulse as the engine rotates. I tested the coil on the distributor shaft(?) and it tested within range. Then checked the resistance of 2 injectors.. each was around 14.5kohms. and besides what are the odds that all injectors are bad...

I just bought a new ignition module hoping that maybe the ECM wasn't getting the signal from ignition module and i plan on putting it in this weekend, but, from what i read, that module also controls spark. And i have spark so i think i may have wasted 40 bucks here.. D'OH!?!

Where do i go from here? Any specific things to check that you folks have seen before? is there a "correct" way to make my injectors fire manually from the harness to check each one individually? - i dont want to put 12 on one side and ground on the other and burn them up.

Sorry for the rant and thanks in advance!

James

Get a working fuel pressure gauge. Just because is sprayed across the room doesn't mean it is enough.

Will check that this weekend and report back. Thanks for the input!

1) Run dry and burnt up... fuel pumps normally can't run dry as they should be wired so, no oil pressure, no run. The run dry more likely relates to the raw water pump. Even 20 to 30 seconds of dry running will kill raw water pump impellers. Even if one somehow managed to run the fuel pump while dry, it is unlikely that it would be damaged unless it was run for a long time ( 5 to 10 mins or longer) dry.

2) If you have spark and no gas unlikely you have or had an ignition related problem if it won't even cough.

3) Check fuel pressure per previous recommendation.

4) If pressure OK, momentarily ( less than a second) applying +12 directly to injector unlikely to damage it.
It is also unlikely that ALL of your injectors are bad... if at least one is OK you should have had the engine at least cough.

Well problem solved. Fuel pressure was 40psi with fuel pump off and ~50psi with pump on. Then replaced the ignition module. Noid light proved invaluable. Found out ECM was pulsing injectors but they weren't squirting. Pulled the injectors and they were filthy with old stale crusty ethanol gas. Got some 5/16" (ID) hose and put it over the injector, put a little carb cleaner in it and blew on it to add pressure. Then pulsed them while blowing with wires from the battery until they were clean. Cleaned out the fuel rail and put it back together and she fired right up like a champ. Thanks for all the help guys.


I do have one question though, is it possible that the ignition module could allow spark but no pulse to injectors?

Pull the injectors and have them cleaned and flow tested or a blown engine is what you will have.

Chris, I cleaned the injectors fairly good. If you don't mind elaborating, how will a dirty injector blow the motor?

One dirty injector will lean out one hole and burn up that cylinder. About $25 ea to clean and flow test injectors with new filters and o-rings..