Requesting help to track down a short, blowing injectorfuses

[grover]

Hi folks. I'll apologize in advance for this being a long post, but want to provide as much info as possible to help in making a diagnosis.

Three times in the three years since I've had my MS system I've had issues where, while driving, I will get very short off/ons of the ignition, like I'm losing MS power very briefly. One time it went away after a minute, the two other times I ended up having to pull over. After a couple of hours the car was eventually able to re-start and get home, albeit sometimes with some further power stumbles. However, it often took quite a few times turning the key for the fuel pump to get any power whatsoever, whereas usually I can hear the fuel pump run for just a couple of seconds if I turn the key just shy of the cranking position. When this issue happens, the fuel pump receives no power, until all of a sudden out of nowhere it decides to be nice to me and fires up. It's worth noting that all anciliary power (radio, lights, etc...) don't go out, it's just power to the motor which I believe is a cut of power to or from the MS system. It is also very much worth noting that the three times this happened were directly after some fairly heavy rains, so I'm guessing there is some sort of a short in the system perhaps caused by moisture (of which NONE can I see anywhere near any of the connections).

Today I tried to start the car for the first time since the most recent issue (it has been dry for a couple of days, so figured maybe things would have dried out) but no go, I got zero power to the fuel pump. However, what I found strange was that in the key position where the fuel pump usually gets power, but shy of cranking, I kept blowing the 5 amp fuses to the injectors on the relay board. I replaced the fuses, tried again, and saw them blow once more. Is it normal for them even to be getting current in this key position? This made me wonder if there was somehow a short between the fuel pump circuit and the injector ciruit.

My relay board is inside the glovebox, so not in a place where it would get direct contact with water, and the ECU is under the passenger seat. I'm running MSII V3 and EDIS. The car will crank, but obviously not fire-up as I'm getting zero fuel delivery and now today apparently blowing injector fuses.

Would love to hear what suggestions you might have for tracking this down. Thanks in advance.

[Bernard Fife]

grover,

First thing I would suspect is D19. There is more on this here: http://www.megamanual.com/ms2/V3trouble.htm in step 14.

Depending on how many injectors you are running, 5 Amp fuses may not be enough if you are running 3 or more low impedance injectors or 4 or more high impedance injectors per bank. Even 2 very low impedance injectors could blow a 5 Amp fuse under some conditions. I would try a 7.5 Amp fuse if this was mine - that's still lots of protection against shorts and should give you some 'overhead' on the amperage.

Lance.

[grover]

Thanks for the quick reply Lance, I'll take a look at the link you provided regarding D19. I actually saw your reply while I was at O'Reilly picking up some new fuses so went for the 7.5 amp ones. When I got home a few minutes ago I remembered that once before when this happened I thought it perhaps had something to do with the ECU not being properly grounded (I just stumbled across this somehow, can't remember exactly what prompted me to think this.) As such, BEFORE changing the fuses, I went ahead and ran a separate ground jumper wire from the MS ECU to a known good grounding point on the body. I then turned the key just shy of cranking and sure enough the fuel pump turned on temporarily. However, the stumper is that when I then removed the ground wire, it still worked. I swear, this is the ONLY thing I did so now I'm completely confused. I then went ahead and put in the new 7.5 amp fuses and the car fired up. Obviously I'm happy that it's working, but would very much like to understand the root cause so I don't have to go through this every time the car gets a good soaking.

Am I incorrect in believing that the injector fuses on the relay board should NOT be getting current before turning the key to a cranking position? Would the fact that it is now working (at least temporarily) remove D19 from being a possible culprit?

Thanks again for the help.

[trakkies]

How is the MS grounded within the DB 37 connector? The injectors use 4 pins (two per circuit) to spread the load, so the ground wires must be of adequate size and connected to at least 5 pins. They should also run direct to the engine block - not through the relay board or whatever.