Bad Injector

[Highway Q45]

Special thanks to Daedalus for e-mailing me the harness testing photos. I got worried after a sudden misfire (no-fire) at all rpm's started out of nowhere Sunday. I didn't think an injector could fail so fast but #4 tests out at 266k with the rest of them at 12 to 12.1 ohms. (Why did it have be #4....pulling the plenum just isn't what I wanted to do...should I pre-schedule my chiropractor visists?) Once I get back to town should I test the wiring at the injector end or is this end of the harness built too solid to fail? Is it wise to just replace the bad one and wait for the next. Are the OEM units from Joe the way to go or are there other options like Accel and Venom? Still can't figure why the CEL hasn't come on though. Any thoughts or hints from those of you who have been there before?

SteveP.s. Knock sensors tested good @ 549K and 545K

[Q451990]

Are the OEM units from Joe the way to go or are there other options like Accel and Venom?

Yes! I tried remanufactured units from Python and had bleed-down problems. It's not worth the trouble and pain to do this job twice. Be sure to lubricate the o-rings with dielectric grease or vasoline to avoid pinching them and causing potential problems.

Heath

[DAEDALUS]

The sudden failure isn't too surprising, but the 266 ohms sure is. You might be able to test the harness without removing the plenum. I had just enough room to get the #3 harness off to test the injector directly...#4 should be about the same I would think. It's a long shot, and either way the plenum will come off, but good to know before ordering parts. The harness is about 1/4 the cost of 1 injector. Personally I would just do the 1 injector. After 2 injector failures, the next one under the plenum to fail will bring me to buying 1-2 new injectors, and then playing musical chairs with the set, putting the newest 4 under the plenum. I've only had 1 failure so far in 4+ years, so the car's been good in that regard.

[Q45tech]

Measuring resistance [in VOM] is an application of R=E/I.....you are actually measuring the current flow from a fixed voltage supplied by the meter.

Shorted turns in a solenoid can sometimes make for weird ohmatic readings which vary by meter model and type.

The injector normally draws up to 1 ampere at 12-14 volts thus the 12-14 ohm spec.

What one needs is an inductive bridge or away to see [clamp on probe and osilloscope] the current ramp up [from application to pintle lift to max current] to really compare injectors.

Just did a 2 step [normal and loaded in drive, AC on] power balance on my 249,000 mile injectors. Try to do this every 90 days to catch problems before they turn into real problems.

No more than 12-13 rpm variance at either 1162 [62-75 rpm drops or 737 rpm [50-62 rpm drops].

249k for me has been over 8,000 running hours and 45,000 operations per hour............360-500 million plus open and closes............about the same as the human heart beat in 10 years.

$1200 seems a small amount of money for something to last that long.

[forecast]

Still can't figure why the CEL hasn't come on though.

Do you have a California car or is it imported from another state (can one do that in California?)

Anyway on the '90 model the CEL only activates on injector trouble in california cars.

[Highway Q45]

My Q is a 91 Calif. model so the CEL should come on with a bad injector. CEL does light with start-up and goes out so I know it does it's thing. The resistance was 266,000 ohms, not 266 and was taken several times with a Fluke Scopemeter. Daedalus, I just got back into town so I will try to manuever my way into the actual injector terminals for a retest. Q45 Tech, could you elaborate a bit on the scope/clamp-on ammeter test? Isn't 266k ohms a bit unusual if it is the injector and not a near open circuit maybe in the harness b/t the injector and 6-pin plug? Again thanks for all the help, any alternative would be preferable to a plenum pull at this point. I should rename the Q "Holiday", every time something goes wrong it's right before a holiday.Steve

[DAEDALUS]

It may need to be totally open for the CEL to come on (per the manual actually). Yeah, I missed the little k. What's 3 orders of magnitude between injectors? Geez, you'd think 266,000 ohms would be enough. It's virtually arcing. Maybe "overtime" would be a better name. Or "the grinch"?

[Q45tech]

You replace the [underhood] injector fuse with a loop of wire and clamp the amplified current probe on the loop. Attach probe to scope and trigger scope from #1 injector.

All injector receive constant +13 volts in parallel after fuse, the ecu switches the ground lead to ground via individual transistors.

8 nice 45 degree ramps [with a little ~ {squiggle} at 55- 66% of peak current] as each injector lifts the pintle then staturates.

The inductance changes as the pintle moves up.

The above test is more precise as you can see all the pintles lift [electronically] [any out of time - sluggish opening]......early lift weak internal spring on solenoid, late lift - varnish or shorted turn.

Obviously all 8 should draw the same peak current [1 ampere]. High resolution probe/scope would allow the after current cut ringing to be visable.http://www.lindertech.com/newsletters/n ... chives.htm

[Highway Q45]

Dennis,Thanks for the great info. I quickly checked out the links you provided and realize again how far troubleshooting has developed since my old days of the "smoke test". There's a link you provided to hooking up Fluke 98 (I have a Model 97 but they are generally the same) for a similar test with the amperage trace removed. 1. I assume I should hook it up with the "dual scope" selection for the ramp up test you recommend? 2. Unfortunately I don't have a clamp-on at the moment; do you think an external shunt (.01 or .001 ohm) in the fuse loop will also work?.

Not having tried this yet I'm pre-guessing obstacles. If the problem was in the harness only I'm curious what the trace would look like. My first effort will be trying to get to and isolate the injector terminals "only" for retesting.

This Forum is just amazing...I've learned more here than I've learned in years of putzing with cars. Cars for me are a hobby not a career but I appreciate so much how you experts are willing to share your skills.

Thanks to All,Steve

[Q45tech]

"do you think an external shunt (.01 or .001 ohm) in the fuse loop will also work?. "

Depends upon the sensitivity of scope.........make sure it is not wirewound resistor as the inductance might change things.

Also use isolated ground on scope unless plastic case.

Why I like an amplied current probe is you need the variable gain to see the minute squiggle of the pintle lift WELL. Easy to check motors, pumps, solenoids...........look at ignition coil primary and reflected back secondary...........current is much more sensitive than voltage.

[Highway Q45]

The shunts I'm referring to are non-polarizing factory calibrated wire type shunts with "ears" to measure voltage drop. They are straight-line manganin wire (.01 ohm/6 ADC 10Mv=1A and .001 ohm/25 ADC 1Mv=1A) I use them for calibrating rectifiers and with dataloggers for recording earth currents in buried structures. The Fluke Scopemeter is actually a Model 99 with a sensitivity of 1mV to 100V/division. The lowest current scaling is 1mA/division so I think it might work OK. I too prefer the clamp-on probes but not as much as the guy who stole it from me out on a job 6 months ago! If this project becomes too overwhelming I'll just toss a grenade into the garage, call Homeland Security, and collect the insurance money. Thanks for all the help.

[DougQ45]

How in the heck does the Tech know all this stuff??? Don't remember reading any of this in the service manual!! My head hurts after reading some of the posts with the complexity of it all. Steve, thats just how my injector went--boom 11.7 ohms to 242 ohms, threw the check engine light, went off after a few moments, then the engine vibrated like a covered wagon on the way to Donner summit.

On the positive side, make sure you plug your intake collector tubes when you pull the plenum so nothing drops down into the abyss.

The correct way to do an insurance job is to have someone steal the car, drain the oil, drive the car till the engine blows, then put the oil back into the car. Then phone in the car as stolen. Much easier than a handgrenade, and saves you the insurance claim on your homeowners policy for the garage demise. Plenty of guys in east LA to do the job for $500 or less.

[Highway Q45]

Actually mine drives OK with the bad injector, just a steady miss and bad stumble at idle. I drove it about 15 miles home and am waiting for a verdict on the correct repair. Did you end up driving all the way back to So.Cal from Tahoe with yours and what did the plug look like after that? Don't worry I'll be careful on the plenum pull, Kragen is running a special on "Runner Condoms" to keep those little surprises out of the way.

Actually on the insurance claim, don't we all need a bigger garage? About hiring "outside" help, wasn't it Dave Barry who said "Why should I pay some idiot to do something I can easily screw up myself"

[Q45tech]

And the award for brand new one of a kind problem goes to a 1994Q with 137,000 miles.

Both precats melted to a solid mass blocking all the exhaust flow on both sides.Courtesy of an ignorant owner who just kept driving as the power dropped lower and lower and lower. He said he had to keep it floored to make the last 45 miles at 35 miles per hour!

Cost to repair $1700 with 2 used exhaust manifolds [10 hours labor] and $10 for a new MAF connector.I am amazed the exhaust valve didn't melt or crack who knows what other damage will show up soon.

Same thing with a bad injector: the misfire no fire will throw the engine balance out and wear the crank/rod bearings.When its not perfect don't drive it.

[Highway Q45]

Thanks Dennis,Now I'm really glad I babied mine for the short drive home after hearing of that 1994 Horror Story. It's really amazing that some of the cars you see out there that have been misfiring with deferred maintenance are alive at all. Does the Q ECU go into a "safe mode" that will get the vehicle off of the road or was all his damage caused by WOT at 35mph? I hope no damage was done to mine from my drive home.

Again thanks for the troubleshooting help, pretty interesting stuff. I'm still trying to figure out how to hook the scope up without the single plug clamp-on. I can't convert mV to amps outside the meter like the clamp-on does. I guess I'll have to use mV as the vertical scale and maunually convert to amps.

[Q45tech]

12-14volts /12 ohms = 1-1.16 amp........more or less what the peak injector draws...........the important thing is all the 8 waveforms peak at nearly the same vertical position and finding some locked horizontal sync that lets you know which waveform is which injector.