Bad injector ? ? ? ? ? ?

[LarryIII]

My 97 Outback wagon has been a little workhorse. It's given good service and is fun in the snow. Though not as much fun as the SVX. The next one we get will definitely have the new 6-cyl. engine.
Yippee for VDC !

[James Scott]

EEEEGADS!!!! IT"S DOING IT AGAIN!!!!

It is now rough idling on startup (60 t0 80% of the time), but not later on high mph (60 to 80 mph) shudder like before!!?

I was able to verify twice yesterday that the "offending" cylinder has remained AT THE INJECTOR CONNECTOR!! [after replacing both the coil pack and the injector for that cylinder!]

SOOOO!, it's either the connector (harness), eeeeeeeECU, or ?

Let me know if you gots any ideas now guys? [How do I check for harness intermittent failure, or intermittent ECU failure, or ?]

Thanks AGAIN! Jim

Jim,

I know your frustration… I used to have a subscription to Alldata.com, but I just checked and my subscription expired. It was an invaluable tool when I was working on my car. You can sign up for $24.95 per year. If I remember, they will lead you through a diagnostic check and tell the voltages and resistance to look for…

Wish I had printed out some of the stuff..

Anyone else ever use Alldata?


Bill

[James Scott]

Well, after all the changes to the cylinder [that had no response to removing the injector connector while running rough] (changed injector AND coil pack), it still does the intermittent rough idle and some higher speed shuddering (neither as bad as before though?).

HERE'S THE LATEST >> Today, while idling rough long enough for me to fool with the engine a little, I removed the "offending cylinder" injector connector and AGAIN NO CHANGE! This time, I immediately checked the voltage at the loose injector connector terminals and got about 13.5 VOLTS LIKE THE REST!!??!!??!! I put the connector right back on to see if the signal had started up after removing the connector, but the IDLE WAS STILL ROUGH!

THIS SEEMS TO INDICATE THAT IT'S NOT THE INJECTOR, THE HARNESS OR THE SIGNAL GENERATOR (ECU) FOR THIS INJECTOR!

SO! IS IT THE SPARK SIGNAL COMING FROM THE ECU OR ?

WHAT ELSE COULD IT BE??? HEEEEEEEEELP!!!

THANKS FOR HANGING,

P.S. My low beams work good anyway!

[Beav]

Injectors work by having their GROUNDS switched on and off. The voltage is always present when the key is in the 'On' or 'Run' position.

[James Scott]

Beav,

Does that mean that one of the wires in the injector connector is the ground wire you refer to? If not, where is this ground?

Since the engine performance remains the same on this cylinder (rear driver's side) when removing injector connector (during intermittent rough idle), doesn't that mean this cylinder is the "culprit" - either injector signal or spark signal not functional intermittently?

Since I got the voltage reading on the connector during rough idle for the "offending" cylinder, doesn't that mean it must be a spark signal intermittent failure?

COULD IT BE AN INTERMITTENT POOR GROUND AT ECU or elsewhere?

THANKS for your expert advice! Jim

[James Scott]

I have started to check the shop manual schematics and troubleshooting guides (suggested by svxistentialist) for voltages and resistance (grounds) on the ECU harnesses (and harnesses on the engine) for continuity, power and resistance to diagnose my SVX's intermittent rough idle.

I found instead of reading the ground terminals @ 0 ohms (connector B62 - terminals 14, 15, 24, and 25 for example) when grounded to my dash area grounds (bolts, large metal brackets, and steering column for example), they read about 15 to 25 ohms when the IGN switch is OFF, 40 to 70 ohms when IGN SW ACC, and 150 to infinity when IGN SW ON!

After checking continuity with engine connectors and engine ground, I found that this "dash ground" has that much resistance to the engine ground ("GE" - intake manifold).

Is this NORMAL??? or have I found the problem?

[When I check the terminals to the engine ground, they are zero. However, when I ground these terminals in the underdash "ground points" available, I get these variable readings!

PLEASE HELP!!

[Beav]

When I mentioned that the injector fires by having its ground switched on and off I was trying to help you by explaining that the positive is always on with the ignition switch, the ground is switched on and off by the ECU. This is backwards from what most people normally expect. Almost every circuit controlled by a control module in a car is controlled the same way.

Now if you were to use a test light while the car was running you would find both wires lighting the test light. Looking very closely you might see the light flicker while testing one of the wires. This is because the 'on' time for the ground is measured in milliseconds, probably around 3.8ms at idle. The reason for this is that the current flows through the ci inside the injector, still looking for a ground. When th ground switches on it is so quick that only a small flicker is noticeable.

Ohmming the grounds may seem the way to go but a more reliable method is to use a voltmeter, Attach one clip to the battery ground and the other to the circuit near the device (preferably at it its connector) you're working with. A voltage drop of 0.1 volt or less is acceptable. You'll need to look at the schematic to determine where the ECU is grounded, I would suspect it isn't just grounded to the dashboard.

[James Scott]

Beav, I don't understand your suggestion this time. To answer your question tho, the ECU is grounded at the point I mentioned - @ the intake manifold ("GE" in the manual).

I was checking ground (and continuities of harnesses) for ECU ground, ignition ground, injector ground and sensor ground as shown in the troubleshooting section of the shop manual. They checked out @ 0 ohms when grounded to the "GE" ground point on the engine (intake manifold), but were variable (15 to infinity ohms when grounded to the underdash ground points!?) What does this mean?

Your comment about voltage drops is unclear to me. Are you suggesting that I check VOLTAGE between these terminals (grounds for ECU) and the battery ground? Or voltage (dropped compared to what?) between battery ground and what other terminals??

Should the two grounds I mentioned: on the engine ("GE" - @ intake manifold) and under the dash ground points be the SAME??? - NAMELY 0 ohms between them (they're NOT!)???

Thanks for clarifying!

[Beav]

This is one of those 'you have to do it to understand how it works' scenarios. Or you can go here and bone up on automotive electrics: http://www.autoshop101.com/ or here and get some pointers on using a DMM: http://resources.mhs.vic.edu.au/scie...multimeter.pdf

If you have a dashboard ground problem I'd be checking the ground cable from the battery to the body, or in the advent that there isn't one there - I'm too lazy to go outside and look - there should be a wire running from the engine to the body somewhere under the hood. If there was a problem with the body grounds I would fully expect to hear that you're having a plethora of problems, not just a bobble in the idle.

[James Scott]

I don't mind boning up, but what do you mean when you say check for voltage drops rather than ground continuities? I don't even know where to start.

Can you get me started?

[James Scott]

Thanks for the explanation, Lee!!