injector question and diagnosis help

[Quickstop [UK]]

OK.

so I have been given a clue about my truck not wanting to run.

Am I right in thinking that wire 439 (pink and black) is B+?

This connects to the injectors through the injector harness which are on a DK BLUE (467) and DK GREEN (468)wire per bank.

I believe that the injectors are triggered by the ECM grounding the required circuit? These two wires go to pins C11 and C12 and shouldn't be earthed correct?

I just tried to get a volt reading on the truck and the problem I am getting is that the harness says that there is 14 volts between 467 and 439. This means that the injectors are grounded constantly and the injectors are open meaning that any fuel pressure floods the engine.

Have I made any mistakes here? Pins 467 and 468 have continutity between them on both ECMS.

Can ANYONE with a running truck please check two things for me?

1) disconnect an injector and test the voltage on the harness at that connection? Do you get 12-13v if you measure across the pink/blk and the blue or the green

2) unplug an ECM and see if pins C11 and C12 (larger of the black connectors) connect to each other electrically.

Both are a 1 minute task with a multi meter.

What could be causing the problem? Fried ECM?

This all assumes that the injectors pulse when the ECM grounds them, not the other way round.

I tried this on two ECMS, both of which allow the truck to start, provide ALDL data and run, until the fuel in the rail is exhausted. Both had C11 and C12 connected (continuity tester on multimeter)

I tested the impedance and they are around12.5 ohms so they are hi z and correct for this truck.

Thanks very much for your help!

Mark

 

[sly dvl]

Re: injector question and diagnosis help

Sounds like a PROM issue. Yes, the injectors are ground controlled and fed a constant 12v through the ign. system. It's possible the ECM is bad, but 2 bad ECM's? Unlikely, but still possible. Pull your PROM and see if you still have a constant ground for the injectors.

 

[Quickstop [UK]]

Re: injector question and diagnosis help

this was done with no power and both ECMs unplugged from the truck.

will try that though....

 

[Quickstop [UK]]

Re: injector question and diagnosis help

where do I get a new ECM from then?

 

[sly dvl]

Re: injector question and diagnosis help

So with the ECM unplugged you still have a constant ground on the inj. wires?

 

[Quickstop [UK]]

Re: injector question and diagnosis help

no, the wires are good. with no ecm there is no voltage across the two.

the pins that the blu/green go to on the ecm are C11 and C12 and with the continuity tester they appear connected.

I didn't see if they were to ground.

I should point out that I haven't changed anything for different injectors or anything like that.

If the pins are shorted together and to ground then that is the source of my problem.

I thought the ECM was good though - what could be causing this?

 

[sly dvl]

Re: injector question and diagnosis help

467 & 468 are the ground circuits for the left bank and the right bank. When you turn the ign on you should get 12v on each wire, since they are fed power from the fuse block. If either of these shows continuity to ground with the ECM unplugged, the injectors will (as you stated) be wide open.

 

[sly dvl]

Re: injector question and diagnosis help

I would suggest killing your fuel pump or pulling the inj. fuse during the above test. Even if it takes 30 seconds to do the test, you'll fill your cylinders with fuel if the ECM is holding ground.

 

[Big Mike]

Re: injector question and diagnosis help

What size injectors are you running also are your injectors high z or low z and was your computer modded to run them?

 

[Quickstop [UK]]

Re: injector question and diagnosis help

OK. I read this entire thread, and I think I finally see what to do. With the ECM connected, and key on, back-probe each wire 467 & 468 with a voltmeter to ground. You should see 12V. If 0V, then the ecm is shorting the circuit to ground.

Your VOM check of the ECM pins is invalid. You cannot check solid state devices with a VOM. As a matter of fact, the Helms manual repeatedly stipulates "Solid-state device. Do not check continuity".

If you see voltage on the circuit with the ECM connected, and key on, the ECM is NOT shunting the circuit to 'earth'.

Cheers,
Dave

Isn't this backwards? If the ECM is grounding the wires THEN I see 12v as there is a potential across the two. If it is not earthed then 467 and 468 are floating. I would expect to see 0v but as it stands I am getting the 12v across the two.

This suggests to me that the inj grounds are permanently grounded and I need to find out why.

This is with the ign on.

pnk/blk - dk blu = 12v (should be 0v)
pink'blk - grn = 12v (should be 0v)
pink/blk - engine = 12v (expected)

What could cause the ECM to ground those injectors on both sides? Is there a signal that opens/closes the injectors?

 

[bezerk]

Re: injector question and diagnosis help

just try your stupid stock injectors and see if that works, i think u are brainbusting this mather since YOU DON"T KNOW WHAT INJECTORS YOU HAVE, if you take 10 min and swap back to stock instead of searsching 100 min what could be wrong, take out what you put in new since that is more lickely to be your problem, than stuff just going bad while sitting still.
if problem still excist. search on.
Mechanics need to thing logics first, than the unpossible

 

[sly dvl]

Re: injector question and diagnosis help

Isn't this backwards? If the ECM is grounding the wires THEN I see 12v as there is a potential across the two. If it is not earthed then 467 and 468 are floating. I would expect to see 0v but as it stands I am getting the 12v across the two.

This suggests to me that the inj grounds are permanently grounded and I need to find out why.

This is with the ign on.

pnk/blk - dk blu = 12v (should be 0v)
pink'blk - grn = 12v (should be 0v)
pink/blk - engine = 12v (expected)

What could cause the ECM to ground those injectors on both sides? Is there a signal that opens/closes the injectors?

I assume you backprobed the injectors rather than 467 & 468 at the ECM. Remember, voltage is pressure, and a voltmeter is simply checking the difference in pressure. 12v on one side (pnk/blk) and 0v on the other side (dk blu) will give you a reading of 12v, and that tells me that your inj.'s have a path to ground (assumingly through your ECM) and obviously shouldn't.
The signal to open/close your inj.'s comes from the ref. pulse out of the ign. module. There's nothing that would command the ECM to hold the inj.'s full open in any scenario.
Did you try unseatting and then reseatting the PROM? I've seen poorly seated (or incorrectly seated) PROM's do some weird things.

BTW - read your entire rebuild post last night. One comment - you da man! :tup:

 

[Quickstop [UK]]

Re: injector question and diagnosis help

Kevin - I did it exactly as you read it - I had a voltage between the terminals and thought I had a bad ECM.

Thanks for the :tup: - it's nice to feel like people like my project - been busting my ass on it for the last 2 years!

Dave - something was definitely screwed up. I didn't get around to doing the back probe test like you said as I got distracted and connected up a test light to the injector harness to see if it flashed with the inj pulses - it did. I guess I made an improvised NOID light.

It shouldn't have done, and the light should have stayed lit when I put the bulb across the 12v like I was saying above.

But it didn't.

So for the hell of it, after Bezerk was slagging me off and with only 30 min before my train home, I swapped out the new inj with my Dad's help and then stuffed the old stockers in.

It fired up and idled with the fuel pressure on the rail!!! It shouldn't have done if I was right, so I obviously made some major mistake. It didn't idle well (42 psi, 3 BAR MAP with a 50# BIN) so I need to either up the psi or get correct injectors in the meantime.

The impedance of the injectors was 14.5 on the stockers and 12.5 on the new ones. I couldn't test it properly so wasn't really testing impedance there on my multi meter. I would like to know what was going on.

Arguing electromotive theory would suggest I know something about it when clearly I don't so I won't waste time - I need to learn and want to know how it works!

But it runs - I'm getting rid of the 50#s which seem plagued with problems and am going to get somer 65#s which seem to be the popular upgrade.

I am so happy right now

 

[sly dvl]

Re: injector question and diagnosis help

This is with the ign on.

pnk/blk - dk blu = 12v (should be 0v)
pink'blk - grn = 12v (should be 0v)
pink/blk - engine = 12v (expected)

Glad you got it sorted out. I'm still puzzled with the above readings though. For my own knowledge, was this test done with the injectors plugged in, or unplugged from the harness?

So it sounds like those 50# injectors were way too big for the application and dumping too much fuel in. Removing the pressure reduced the fuel quantity being delivered and it ran until the pressure was depleted. At least, that's the way I'm interpreting it :dunno:

 

[Quickstop [UK]]

Re: injector question and diagnosis help

the test was done with the entire harness disconnected from the injectors and testing the ECM side of the harness.

I think your interpretation is correct, although it doesn't explain hwy the 50 BIN I had was dumping so much fuel in with injectors that it was designed to control.

Do different 50s put in different amounts of fuel?

I am away from the truck for 2 weeks now so can't take any snaps, Rene told me his truck ran on 65s and 50s using the same BIN I had so I don't understand it.

I'm ordering 65s as I'll need them anyway later so may as well get them dialed in now. WIll be interesting to see if the same problem presents itself.

 

[dgoodhue]

Re: injector question and diagnosis help

Since you said your injector aren't being pulled low enough, my first instinct is you have a ground issue.

Do you have all your grounds on the back of the heads connected? Are they make good contact (ie not heavy thick new poweder coating) Did you relocated your battery and the ground path becak the ecm is poor?

 

[Quickstop [UK]]

Re: injector question and diagnosis help

ground pulls the injectors open - the problem was they were STAYING open by the looks of it.

battery relocate was for the turbo but I have some 25mm2 cable grounding the heads to the frame and no other ground issues to speak of. Running solid motor mounts as well so I get good earth.

It started first time with the stock injectors and they don't run that much current so I don't think I havea ground issue.

Happy to be wrong though?

 

[sly dvl]

Re: injector question and diagnosis help

the test was done with the entire harness disconnected from the injectors and testing the ECM side of the harness.

Ahhhhhhh, this explains your 12v reading. Since the driver for the injectors is (presumably) a transistor, there would have been a very slight path to ground when you checked it with a Voltmeter. Voltmeters have an extremely high amount of internal resistance (like over 200M ohms) so as not to affect the reading on the circuit you're testing. Since you had voltage on one side if the inj. plug, and a very slight path to ground through the ECM driver, you would get a 12v reading on the meter.
But, when you connected the load (inj., noid light, or in your case, a test light) the transistor would not allow enough current to flow through it to operate the load.

For future reference, always check voltage drop with the circuit connected and live. This will give you a much better indication of what is actually going on. For example, if you'd done the same test with the injector plugged in and everything hooked up and turned on, you would have gotten a 0v reading.

I don't know nearly enough about the "tuning" end of things to understand why your BIN and 50# inj.'s worked on another truck, but not yours. I'll leave that to the tuning pro's.