nunnink23

Hello all. I have a 2000 VP 5.7GSI TBI injected motor which had an oil pan issue last fall. The engine ran great all year, but I pulled the motor to do an oil pan over the winter. Along with the oil pan I replaced a few other items, had the valves lapped, stem seals replaces, replaced the oil pump, injectors rebuilt, and I rebuilt the TBI.

4 weeks ago I dropped the engine back in, buttoned everything up, and she wouldn't start. I went through the normal tests. First verified that I had spark, which I do. Second I verified that the injectors were spraying, which they were. Third I verified compression - 175 PSI Max at all cylinders, 90 PSI first bump. At this point I decided to pour a little fuel in the intake to see if the problem was fuel related. The engine fired up immediately, ran for 3-5 seconds until it started starving for fuel and slowly cut out.

Knowing this must be a fuel problem, I did the following items: BTW - I have a native MEFI III motor, but with a MEFI IV computer and conversion harness, since it died three years ago in the previous owners hands.

1. Verified fuel pressure - 6PSI low pressure pump, 30 PSI high pressure, measured at the TBI.
2. Verified fuel volume just in case - will fill up a coffee can in 2 seconds.
3. Sent my injectors BACK out to an independent shop to be flow tested again, just to be sure the first place didn't make a mistake. They checked out fine.
4. Rebuilt the TBI AGAIN, just to make sure I didn't tear the diaphragm the first time. I don't think I would get a proper fuel pressure reading without a working diaphragm, but just to be sure I did.

Nothing changed at this stage, so then I figured my problem was electrical.

I pulled the codes, and I had a myriad of them, but all were due to me cranking with items such as the MAP or TPS disconnected trying to override a faulty sensor if that was causing it not to run. I tried disconnecting the S.L.O.W sensors, and this made no difference.

My marina suggested that even though my injectors were spraying, and pulsing, that I should put a NOID light on it. I did this, and it flashed rapidly. I don't know how bright they typically flash, but mine seemed a bit dim, so then I figured my problem was voltage or ground from the injectors. I checked the following items at this point:

5. Verified that my injectors had B+ voltage at the hot lead (with a multimeter). The battery had 12.58 V, injectors 12.47 V.
6. Traced the injector ground wires back to the J1/J2 connectors and checked for continuity, then traced the same wires through my MEFI IV conversion harness, and also had continuity.
7. Traced and checked all the ignition module wires back to the ECM and checked for continuity.
8. Traced all four MEFI IV ground pins to the ground wire, and checked for continuity.
9. Checked both my engine post grounds for abnormal resistance.

After getting this far, I decided my injector drivers must have died in the ECM. I sent my ECM to OBD Diagnostics to be bench tested. He called me two days later and said the unit was fine.

After getting my ECM back, I replaced the ignition module, and coil - not sure why, but somebody at my marina suggested I do this since he had a similar problem and it turned out to be these. No change in my condition after replacing both.

Now I do not know where else to turn. I apparently have a good ECM, new ignition module and coil, good spark, good compression, good injectors, good fuel pressure, and yet my engine wont start. If I let it sit all night, it usually will sneeze on the first few cranks of the day, but that is all. As it was before, if I pour fuel down the intake, she will start up and run until it starves for fuel. The engine has set codes before, but as I said they will never come back unless I disconnect a sensor or connector, so there are no hard faults.

I am getting a bit desperate at this point, since even my local mechanics are confused. I am considering buying a SBC TBI off a GM truck locally just to try to start my engine, and if it runs then I know my TBI is bad SOMEHOW, even though the injectors have been tested twice, and TBI rebuilt twice. For whats its worth, I don't know what injector post resistance is supposed to be, but mine is 1.5 OHMS.

Should I just by the Diacom tool and start reading sensors? Or should I pull my harness out of the boat, unwrap it and trace every single wire/check it for continuity? I also ordered a new MAP sensor just because I want to rule it out - even though I am told disconnecting it will set the ECM in a default that should allow it to run, and this didn't change my condition.

Any help would be greatly appreciated. If anyone needs a diagram drawn of the MEFI III to IV conversion harness I can do that.




,

smokin' gun

have you tried replacing the temp sensor .the one for computer .it sounds like a cold start issue and your needing fuel at cold start .just a thought. if the sensor is bad the engine thinks its warm .and will never start cold

nunnink23

Good morning. No I haven't yet - but I will now just for the heck of it. I thought disconnecting these sensors should set the ECM in a default, but maybe not. I will see if I can find one today. This is why I want the Diacom tool. If I read the ECM and it said the temp sensor is reading 180 or something like that, I would know that's throwing off the mixture.

Honestly though, the injectors are not spraying a lot of fuel. Not enough to even get the plugs wet. It soaks the butterfly, but I don't even see it in the intake. You would think that after cranking for 15 seconds straight it would at least sputter or cough. All the gaskets in the engine are brand new, and I was very meticulous putting it back together.

I am trying to start the engine on the trailer, with the muffs off. I probably need to put a new impeller in now because I have cranked it so much with a dry impeller, but that is the least of my concerns now lol!

nunnink23

Just ordered a coolant temp sensor $22 bucks not bad! I will have it tomorrow but cant put it in till Sat.

Edit: It is the computer one btw.

92nsx

Keep us updated as for what you find out

nunnink23

Will do. In the meantime does anyone have other ideas of what to check? I was told by two mechanics who are too busy to work on it now due to the start of the season that "this is the strangest no start condition I have ever seen". I would gladly have a mechanic look at it, but they are all at least a one month wait right now. Unless anybody here is located in the CT Fairfield County area.

3pointstar

I'm not an expert - so please take this with a grain of salt...

1. In your message you said that if you pour fuel in - it will start and run. Have you checked the ventilation within the fuel tank- I know this sounds stupid - but a few neighbors have had issue with the vent being clogged and their engines did the same thing as you describe.

2. Can you bypass the fuel filter and run gas directly into the injector system. -- I really sounds like you have something clogged.

again I'm not anywhere an expert - just can't stand a fellow boater on dry land

keep us posted

3pointstar

nunnink23

Me either! This is not a great start to the season. Not to start whining, because boats are by nature a lot of work, but holy crap this thing has been a nightmare this Spring!! This summer is my last before grad school, and the CPA exam, so I want to enjoy every bit of it!

In regards to your suggestions, I have a new fuel filter, and I have tried putting the fuel line in an independent fuel tank, just to rule out the problems you brought up. I forgot to mention that in my post. It just seems like the injectors are not spraying enough fuel.

I was worried about that too until I took of a fuel supply line at the back of the TBI and saw how quickly it filled up a coffee can. And its not bad gas because I have been dumping its own fuel in the intake.

BTW I am not an electrical expert, so my OHM readings are probably wrong. On the 200 scale I think 1.5 (injector posts) means 300 OHMS right? My grounds on the 200 scale have .3-.5 OHMs.

28Eliminator

Sorry to hear about your problems. I don't know much about how the 5.7 is setup, other than the temp sensor, what about the lanyard switch being bad. I can't tell you how many of those I have replaced and it's always in the spring after they sit for an extended period of time. Not sure how Merc uses that on the 5.7 to control it not starting, but thinking out load. Also is the fuel pressure at 30 when cranking, and is 30psi what the manual calls for on the motor. If it calls for 35 and you only have 30, I wouldn't expect it to start.

nunnink23

The manual calls for 28-32 PSI, and it has the when ignition is on, and when cranking.

Voltage drop at the injector hot leads is about 2v when cranking. From battery voltage to about 10.5 - 10.8 volts. I assume that's normal since the starter motor draws so much power.

I just keep coming back to the injectors not spraying enough fuel.

My safety switch wont even let you power the ignition on. You need it plugged in or the entire engine/dash is dead. The shift interrupt system will allow ignition on, but not cranking.

I will actually have the temp sensor tonight, but I wont be home till its dark. And tomorrow I have a wedding to attend in the afternoon! Damn!