1.8 injector no or low voltage

22803 Views 40 Replies 6 Participants Last post by turbovag161, Jan 19, 2014

bugman79

Discussion Starter · Jan 7, 2014

Does anyone know how much voltage should be at the injector plugs? I just bought this 99 beetle for $500 and it has some problems I can't figure out. I'm getting a misfire code for cylinder 4. (1240) 1-3 plugs have 3.49 volts and cylinder 4 had nothing so I swapped the ecu out with a used one and now it has.75 volts. I know spark is good, so I pulled injectors out of the manifold and 1-3 injectors fire fuel and nothing out of cylinder 4 when I crank engine. No voltage when key it off, don't know if that helps. I'm also getting codes 1542 & 1544, but I think those are a different problem. I'm getting a vag-com in a couple days, right now I have just a cheap code reader.Thanks in advance. Troy

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jfoj

· #2 · Jan 7, 2014

I have not looked a the wiring diagram closely, but usually the coils and injectors have the negative or ground side controlled by the ECM. So this typically means the coils and injectors should have 12 Volts present when the key is on.

Use a test light to see if the ECM is actually trying to trigger the injector for that cylinder, you may need to use a LED if the test light does not work, but you can try the test light on a known working injector fist. Remember you connect the test light clip to a positive battery source for this test as the ECM should control the negative/ground side of the circuit.

Probably a broken/damaged wire somewhere near the injector?

bugman79

Discussion Starter · #3 · Jan 7, 2014

Thanks for the reply. I stripped the harness all around the injector and couldn't find a break. The smaller gauge wire to injector has the voltage, I checked with the ground on the neg.battery terminal, the others are supplied together in the harness. With low voltage on 3 and almost nothing on the 4th I'm wondering if it's the ecu. I traced lines all the east to the ecu and it all looked good. I'm soooo stumped on this one...

Thanks for any help
Troy

jfoj

· #4 · Jan 8, 2014

Looks like from the diagram the ECU ground the injectors to trigger them?

Seems that the injectors should have 12 Volts when the ignition is turned on.

See attached PDF.

bugman79

Discussion Starter · #5 · Jan 8, 2014

that is absolutly correct. i've talked to others about this and your right. it should be 12 v and the ground goes to the ecu. I checked fuse 32, it was not blown but only has 3.49 v going to it so i'll have to find the feed line to find out why its not 12 v. does anyone know if there is a relay before the fuse or does that get fed right from the battery? the battery has 12.47 V and is 5 days old. is there anything else i should look for that would cause this low voltage?

jfoj

· #6 · Jan 8, 2014

I think the fuel injectors get their power also via the fuel pump relay??

You may want to swap or replace the fuel pump relay? Not sure on the VW, but on many of the BMW's the horn and fuel pump relay are the same and can be swapped. Usually the like relays are the same color.

Hope this is the case, I will see if I can figure out the wiring diagrams, I have them electronically and they are not very well linked from section to section.

bugman79

Discussion Starter · #7 · Jan 9, 2014

Just tried a new fuel pump relay......still only 3.49 v at the fuse.....what's left? ECM?

PRM502STREET

· #8 · Jan 9, 2014

Doesn't only the ground signal come from the ECM?

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jfoj

· #9 · Jan 9, 2014

bugman79 said:
Just tried a new fuel pump relay......still only 3.49 v at the fuse.....what's left? ECM?

If you have low Voltage at the fuse, you are likely getting closer.

Check the fuse box on top of the battery and the smaller wire that connects to the fuse box on top of the battery.

I will see of I can find a diagram that shows how the fuse are powered.

Red99 has a pretty good understanding of the wiring diagrams, I do not get along with them to well yet.

bugman79

Discussion Starter · #10 · Jan 9, 2014

jfoj said:
If you have low Voltage at the fuse, you are likely getting closer.

Check the fuse box on top of the battery and the smaller wire that connects to the fuse box on top of the battery.

I will see of I can find a diagram that shows how the fuse are powered.

Red99 has a pretty good understanding of the wiring diagrams, I do not get along with them to well yet.

the messed up part is that the voltage at the fuse is what i'm getting on the ECM lines at the injector, and i get nothing where the voltage should be. they seem to be reversed somehow. Someone suggested i cut the positive wire going to the fuse and splice in a jumper line with 12 v to see if that gets to the injectors. what do you guys think? Good Idea?

jfoj

· #11 · Jan 9, 2014 (Edited)

I am not sure I am following all of what you are saying?

Forget about the ECU/ECM at this point.

You need to figure out why there is not battery power at the fuse.

I am just tossing ideas out at this point as I am not sure we are on the "same page" at this point?

Ignition switch, relays, ground points (under battery tray are a lot of ground points that can get corroded), fuse box on top of the battery, wiring to fuse box.

You need to focus on why there is not battery power at the fuse, is this the same for other fused in the fuse box?

I would look closely at the fuse box on top of the battery, it looks like Fuse #2, 50 Amp fuse in the box on top of the battery may be an issue? These fuse boxed melt and the connections get bad.

See less See more

bugman79

Discussion Starter · #12 · Jan 9, 2014

There's actually power at the fuse but it's only 3.5 v. The rest of the fuse panel is normal 12 v. I've checked the fuses on the battery but I'll pull them apart to see if I've got voltage there. I haven't checked the ground under the battery yet, I'll do that tonight. There's 3 power lines running to the relays under the dash and they all have 12 v. Seems from there to the fuse is the issue. There is no relay plugged in next to the file pump relay.....should there be something there? I can't find any info on that.

jfoj

· #13 · Jan 10, 2014

Relay position #3 is typically open from what I recall.

If you are 3.49 Volts at the fuse, sounds like a bad connection on the Positive path and not a ground?

I would focus on the lack of 12 Volts to the fuse, but make sure you know what side you are actually expecting the 12 Volts on.

You might be able as a test to use a similar size fuse that does have 12 Volts and jump temporarily to the side of the fuse that should fee the injectors and see what happens.

Good luck.

bugman79

Discussion Starter · #14 · Jan 10, 2014

That's a good idea to try. I'll try tonight and see what happens

Thanks for all the input......I need all the help I can get on this one!

bugman79

Discussion Starter · #15 · Jan 12, 2014

Here's the latest....I've discovered that my injectors will have 12 volts to them if the battery ground is disconnected, but only 3.5 when it's connected. Must be a ground or a short somewhere I'm guessing....any ideas?

jfoj

· #16 · Jan 12, 2014

Suggest you use a test light rather than a Voltmeter.

You can see a dimming of the test light when Voltage is low and a test like slightly loads the circuit.

When you mean the battery ground disconnected, do you mean the negative cable is disconnected from the battery and you connect between the battery negative post and measure the injector hot wire and get 12 Volts?

bugman79

Discussion Starter · #17 · Jan 12, 2014

Yes to your question

bugman79

Discussion Starter · #18 · Jan 14, 2014

Here's the solution to my problem. I finally figured it must be s short between the power and ecm lines going to injector 4 somewhere in the wiring harness. Rather than tear it all apart to find where to two lines had crossed, or replace the entire thing, i traced the line back to the ECM. I clipped the line at the ECM and clipped the line at the injector and spliced in a new line between the two. Whala! Problem Solved! Injectors all have the same votage running to them. I pulled the injectors back out of the manifold to confirm that i had fuel fireing out of each.

Now to figure out my pedal and throttle body problem. :-(

Thanks to all for your help. Many heads are better than one FOR SURE!!!

PRM502STREET

· #19 · Jan 14, 2014

Yay!!!!

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jfoj

· #20 · Jan 14, 2014

bugman79 said:
Here's the solution to my problem. I finally figured it must be s short between the power and ecm lines going to injector 4 somewhere in the wiring harness. Rather than tear it all apart to find where to two lines had crossed, or replace the entire thing, i traced the line back to the ECM. I clipped the line at the ECM and clipped the line at the injector and spliced in a new line between the two. Whala! Problem Solved! Injectors all have the same votage running to them. I pulled the injectors back out of the manifold to confirm that i had fuel fireing out of each.

Now to figure out my pedal and throttle body problem. :-(

Thanks to all for your help. Many heads are better than one FOR SURE!!!

Did I miss the throttle pedal and throttle body discussion?

What problem are you having with these?

BTW, are you aware that the O2 sensor heater wiring can short out and and damage the common ground within the ECU and cause the drive by wire throttle system to not work?

You might want to read this and the links within the post - http://newbeetle.org/forums/2-0-liter-gas/64129-throttle-body-issues.html

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