Fuel Injector Resistance Results - Good or Bad?

[lino]

Thanks to Wes once again for his continued and unconditional support. I completed the test on my 91 Q45a, and here are my results:

[Q45tech]

Well you at least know which one is failing --------#6.......almost 11% above average.

Never seen a flow vs resistance graph however it might be similar to a flow vs voltage............in that +10% might be a -5% change in flow [sqrt of ratio].

-5% is in the correction range of the O2 sensor at cruise and each of the 3 normals would need to be only +2% richer to make the bank read normal

[goody90q45]

I've replaced 4 injectors so far and all 8 are currently reading 11.8 - 12.2. I believe the new injectors come in at around 11.8 out of the box. As Tech said all your injectors reading in the 12.X range could be a function of temperature or the accuracy of your DVM. Did you check your DVM with a 10 ohm resistor?

What stands out is that #6 is out of family. It's probably not causing you any issues (that you'd notice) right now but the resistance will soon (6 - 12 months?) start to rise. I keep a spreadsheet tracking the resistance readings and this is the pattern I've seen with all 4 injectors that have gone bad.

Good luck. Too bad it couldn't have been #1, #2 or #8 going south on you.

[Q45tech]

USE BG44k every oil change to try to wash out the corrosive components in the fuel you purchased that caused the problem in the first place.

The last time [Summer] I measured my 311k injectors they were all with +- 0.4 ohms...............as they were when they were first installed in Jan 1990.

Only 4 full rail flushes along the way, roughly every 60-70k.

[lino]

Well you at least know which one is failing --------#6.......almost 11% above average.

How bad is 11%?

I've replaced 4 injectors so far and all 8 are currently reading 11.8 - 12.2. I believe the new injectors come in at around 11.8 out of the box. As Tech said all your injectors reading in the 12.X range could be a function of temperature or the accuracy of your DVM. Did you check your DVM with a 10 ohm resistor?

I did not. Can you please tell me how to check my DVM witha 10 ohm resistor? Also, is there a time that is better to check, for example when the car is warm or cold?

What stands out is that #6 is out of family. It's probably not causing you any issues (that you'd notice) right now but the resistance will soon (6 - 12 months?) start to rise. I keep a spreadsheet tracking the resistance readings and this is the pattern I've seen with all 4 injectors that have gone bad.

What kind of issues will be noticeable when the resistance starts to rise?

Good luck. Too bad it couldn't have been #1, #2 or #8 going south on you.

Is 6 hard to get to?

[goody90q45]

1) Can you please tell me how to check my DVM witha 10 ohm resistor?

2) Also, is there a time that is better to check, for example when the car is warm or cold?

3) What kind of issues will be noticeable when the resistance starts to rise?

4) Is 6 hard to get to?

1) Put the probes of the DVM, in the ohms resistance setting, on the leads of the 10 ohm resistor. It should read very close to 10.0.

2) In my experience the resistance rises in a warm engine as much as 0.8 ohms. For me, the readings are more meaningful from a cold engine.

3) With one dead injector I didn't notice any change until I replaced it and then the acceleration, throttle response and gas mileage was definately improved. Others may have had differnt experiences.

4) You can replace #1, #2 and #8 injectors without touching the plenum. For all the others you will have to loosen and shift, or completely remove the plenum to get to them.

Removing the plenum is not as hard as we make it sound, you just have to stay organized so you can remember how to get everything back together. Go to Q45.org for step-by-step instructions. There's many other things (hoses, KS, harnesses) that could be replaced once you've got the plenum off but I'll let others preach to you about that. Good luck.

[maxnix]

There's many other things (hoses, KS, harnesses) that could be replaced once you've got the plenum off but I'll let others preach to you about that. Good luck.

Ignore old and worn out under plenum items at your oen peril that will have you pulling the plenum again, and again, and again, and again as each fails because you didn't replace it with a new one the first time you were there.

[lino]

Thank you Mike and thank you Brian for all help. I'm going to buy a resistor and try the test and then do the injector test once again when the car is not warm to be sure.

If it turns out that I have to remove the plenum, what parts are the common ones to replace on a 150,000 mile Q that might very well have all original parts on it?

[maxnix]

KS and harness, all under plenum hoses (including fuel hoses) and gaskets (there are several threads here and in the Q45 Forum and also an Article in the Article Forum). Clean the interior of the plenum and the throttle Body, IAC and EGR valves while you are at it. Good time to do the vavlve cover gasket also since a lot of stuff will be out of the way. Thermostat also, if original. Clean between condenser and radiator and clean both. Refresh coolant since you will have to drain some anyway.

[lino]

I bought the resistors from the Source by Circuit City today. The box came with 4 resistors. 2 are 10Ω and the other 2 are 33Ω.

My DMM has a Diode tester setting. I tested both resistors on it and here's what I got:



On the other hand, when I set the DMM at 200Ω, I get a reading of 10.1-10.2 for one resistor and 32.9 for the other. This is the setting I used to take my readings the first time. I could not get it to give a reading of 10.0Ω and 33.0Ω. It's too late tonight to do a second test, so I'll do it tomorrow and post my results.

[Q451990]

I think your VOM is fine... +/- a tenth of an ohm isn't much variance for these purposes. And how do you really know if it's the resistor that's off a little or your meter? Without professionally calibrated equipment, I don't think you would ever know...

Just for fun, make sure your batteries are fresh in the meter...

Heath

[Q45tech]

Learn to read the color code bands on resistors................including the tolerance band.

Obviously a 5% tolerance 10 ohm resistor could read 9.5-10.5 ohms why you buy a 1% so 9.9-10.1

[lino]

Learn to read the color code bands on resistors................including the tolerance band.

Obviously a 5% tolerance 10 ohm resistor could read 9.5-10.5 ohms why you buy a 1% so 9.9-10.1

Thanks for the pic. Do you happen to have one that is larger or clearer? I donloaded it but it's hard to read - kind of small.

[lino]

Thanks for the tip Heath. The battery is brand new. I just put in the moment I did the test. The DMM is new and didn't come with battery so I had to buy a new one.

I did the test again and the results are the approximately the same. All read 12.7-12.9 except #6 which still read 14.3. I have noticed a vibration at idle when stopped at a traffic light too. Step on the trhrottle and the car launches like a rocket most of the time.....the other times, it feels like the car is starved of fuel for a couple of seconds and then the power kicks back. If I do a fuel injection system clean, like BG, should that change the results I got, or am I wasting money and the real soluton is to change the injector?

[goody90q45]

A rail fush / injector cleaning / BG additive is not going to change the electrical resistance of your injectors. It will soon be time to replace injector #6. Sorry for the bad news.

[Q45tech]

How do you know a PROPER RAIL FLUSH [BG fuel injector cleaner plus a splash of BG44k.........secret sauce in pressurized container] will not change the readings which were caused by a chemical from the fuel leaking/eating into the sealed windings and connector terminals?

Before I pulled a plenum and sent injectors out for cleaning I sure would hook up a rail flush and massage the pressures to optimize the cleaning process...........33>43>55- 60>43>33.

Important to read injector resistance both COLD and HOT as weird things can happen at extremes.

[DrewQ45]

Ahh Tech... that color code chart brings back memories or Electronics School.....

Bad-boy-rape-our-young-girls-but-Violet-gives-willingly (or Willy)...

This is a great post, I was always under the impression that an injector would have to be pulled to check resistance. Any chance of a misread due to any other components in the line? Also, should the battery terminals be disconnected when testing? I'm checking mine this weekend even though I'm having no adverse symptoms. BTW, my 90' (205K) ticks pretty audibly at idle and you once told me that it's the injectors...anyone else experience this? It's been ticking ever since I got the car so no percieved danger.

[lino]

I just did the test again...this time while the engine was cold.

The results are as follows:

12.4 ---- 12.4 ----- 16.6 ---- 12.512.4 ---- 12.5 ----- 12.4 ---- 12.4

Some of them would fluctuate between 12.4 and 12.5.

[Q45tech]

If one was lucky enough to have an inducance bridge you could also measure the mHenries of the coil turns [looking for a shorted turn from the solvent removing the insulative varnish from the wire.

1 turn shorted won't drop the resistance reading just the created magnetic field............slower opening time.

http://hyperphysics.phy-astr.g....html

http://www.findarticles.com/p/...68886

http://web.mit.edu/aaclab/pdfs/nato_jp.pdf

With a current probe and digital osciiloscope you can see the current ramp and the ~ when the pintle lifts off it's seat and of course the resistance and current tells you the magnetic field strength as confirmed by the time to pintle lift.

[lino]

I thought I'd do the test again while the car was cold and was curious to see if the BG44KL can I used would make a difference. Well, it didn't. Here are my current results:

[maxnix]

While #6 is still a goner, the others are much closer to specification.