squaz

Here's my problem,I have a rebuilt HP 500 EFI complete rebuild top and bottom with no modification just better piston rings and some other normal upgrades done on rebuilds.The injectors sent out for cleaning and checking pattern and flow of fuel,came back with print out of tests.Engine starts but searches for idle just plain running ruff.ran good enough to get 1800 rims to set base timing to 8.Pulled plugs and 2,8,and 7 are as clean as they came out the box.I verified that I have spark they are dry as can be.I have checked that there is 12 volts to the red wire on each injector,I checked that there was continuity between the 4 injectors with green wire and the 4 with the blue wire.That tells me the wire harness isn't the problem since #7 is a green and #2 an 8 are blue.4 injectors fire at a time on the 2 different circuits(blue and green)if it was a bad wire I would loose all 4 injectors on that circuit if I' m not mistaken.I check fault codes,fuel line pressure,even tride another set of plugs.Any other things I can check.
Thanks Guy

JaayTeee

I sent 2 sets of 500EFI injectors out to have cleaned a couple of years ago.
( nothing wrong with them just preventative)

The first set was fine, the 2nd set had 2 injectors that were dead, ended up just ordering
2 new injectors

squaz

That's kind of what I was afraid of,those injectors aren't cheap.I bought the Merc. scan tool to check for faults and the cable for test fireing the injectors is on back order,go figure.Thanks for the help

tunertech

just measure the resistance across the injector to determine if it is bad. Should read between 10-13 ohms resistance

squaz

I pulled all the injectors and checked the resistance on them and they're all between 12.8 and13 ohms.Is it possible for the resistance to be ok but the injector is stuck closed.I know I have 12 v to all injectors and I verified that the dark blue wire to the 4 injectors has continuity back to the pin at the ECM connection and did the same with the dark green circuit for the other 4 injectors

blarge

Squaz: I have the same problem with my 502 Marine engine. MY engine runs fine at speeds over 1500 RPM, but has a very rough idle. All eight of my plugs look the same and look like they are firing OK, I have about 20 degrees of advance from the info gained by using the timing light, and the fuel pressure is 40 psi at idle. I sent all the injectors out for cleaning and they look fine on the data sheets that came back with the cleaned injectors. Keep me posted as to what you find wrong with you engine so I can fix mine too. Thanks, Bill Large

TahoeRick

Does your motors have a crank sensor? Check wiring for any corrosion or bad connection

Mr Gadgets

You can fire the injectors by putting 12v on them, you should be able to hear them click open. I use carb cleaner to back flush them onto a white paper towel to see if there is any debris in them. Yours are high Z injectors, so opening them with raw 12 v won't over heat them. With low Z injectors you need to limit the time the 12v is applied. I turn them on and shoot the carb cleaner through them and shut them off without issues.

Fireing them on the bench will tell you if they open and if there is an unobstucted path. Then you can look at what is telling them to open. If the ECU is not doing it's job, it can cause this issue.
I have seen two injectors not fire on a batch fired string of 4 due to PWM issues, but that was with low Z injectors and not a Merc ECU.
Hope that helps.
Dick

offshoredrillin

Call dave at mdg, i was watching him test some the other day. He found out some great info about fuel pressure with stock injectors.

squaz

Well I just put 12v to each injector and 2 ,8,7 don't make a sound 4 of them click and then buzz and one just clicks.Tis is probably a dumb question but at 320 bucks a pop I have to ask.Since the resistance is ok on the bad injectors can they be repaired?Can you just replace 3 maybe 4 or do you change them as a set.