misfire questions

[jettsetter4life22]

ok guys got a day off on tuesday finally going to track down this misfire need some help. patient is 1990 q45 new used engine 60k on it. if have a consistent misfire for the most part but its really bad in the cold mornings as can be expected with any mis. im somewhat confident its either an injector or a bad coil but im not sure yet. does anybody know a way to ohm out possiblly hook up my osciloscope to each injector harness and look at some wave forms without taking the plenum off. i realize its probly time for upper plenum gaskets and hoses anyway at this mileage but a really wanted it diagnosed before i take it apart. i put new ngks in it about 2k ago and of course that didnt fix it so. any shortcuts/ input would be greatly appreciated i love this forum and have just been really impressed with some of the teamwork ive seen on this forum i wish half my crew would work this well together!

bryan

[96Qowner]

You probably have a bad injector. Ethanol is death to the Q45 injectors - seeps into the injector housings and makes them swell, pulling the windings apart internally.

Check 'em with these instructions:

http://www.q45.org/ohminjectors.html

[jettsetter4life22]

ok im confused your saying to ohm out my injectors (electrical resistance) with my voltmeter. if im using a voltmeter im measuring voltage. if im measing resistance should i be using an ohmeter with no voltage applied to the circut. can you please clarify here. thanks for the input and help

bryan

[Q45tech]

Most meters are combo meters in that they measure voltage, current, resistance, and other parameters depending on selector switch position.

Side note: The low resistance scale is the most demanding inthat it exhausts the internal battery very quickly and as the battery declines so does the low ohm accuracy..............short the leads on low ohms can destroy an internal battery in a few minutes.

A 0.1% low ohms Full Scale Accuracy [1000] means at 12.000 ohms the reading might be 11.0--12.00--13.0 and still be considered very accurate.

A 0.05% FS accuracy ~~11.5----12.00-----12.5

Finding a 0.01% accuracy is expensive.

I have purchased a 1% PRECISION 12.000 ohm resistor to calibrate which can still read:11.88-------------------12.12 ohms and will vary with ambient temperature.

JUST AS THE COPPER WIRE COIL IN INJECTOR VARIES WITH TEMPERATURE.

Be careful in buying under $20 VOM even on ebay a decent rugged accurate unit should cost $30-$50.

Make sure the unit has more than 4 digit readout ~~ 12.00 ohmsas reading home ac voltage ~~120.0 is minimalistic

[jettsetter4life22]

ok thanks q45 tech but my question still wasnt answered really. i have a fluke 88 so thats what ill be using so what do i do here am i putting my negative lead to the negative terminal with the battery disconnected and then the positive lead to each pin on the injector harness connector as outlined in the service procedure (ohming injectors) previosly posted in this thread. any clarification would be greatly appreciated man i really just need to find out which and how many injectors i need to get before i take off the plenum. this is my daily driver so i cant really afford more than a day turn around time on the operation on my baby or a would have to sleep at the shop if ya know what i mean. i appreciate it HAPPY THANKGIVING TO EVERYONE!!!

[maxnix]

GoodyQ45 has posted the injector and KS harness plugs on top of the plenum several times. Do a quick search as those may help.

Happy Thanksgiving.

[goody90q45]

You've got it backwards but I agree it sounds like a dead injector (or two). This procedure will take you less than 10 minutes:

For the injectors- positive probe of meter to battery positive terminal, negative probe to each FI harness pin.For the knock sensors- negative probe of meter to battery negative terminal, positive probe to KS harness pin.

> Set voltmeter to the ohms resistance setting.> Key in off position. No need to disconnect battery.> Check them cold (in the morning?)

[Q45tech]

Study FSM and wiring diagram.

The injectors are all tied together on the positive side at the injector fuse then to + terminal of battery. The negative side of injectors SEPERATELY go to ecu where they are sequentially connected to ground [via 8 different transistors] to complete the circuilt.

[jettsetter4life22]

the results are in #5 injector 130ohms so i guess im off to the junkyard. does anyone have any new injectors for sale? thanks so much for your help guys

[maxnix]

Read 1990Q45 thread on after market set he is trying or get new OEM (just missed their additional 10% off sale) form

http://www.infinitipartsusa.com

Why one would want to replace a failed used injector under the plenum soon again is beyond me.

[jettsetter4life22]

ok i took out the #5 injector and well i dont see any coloring on it nor can i see any coloring on any of them. so which color spray pattern injector is the #5 cylinder (orange/blue/ or no color) so i know which one to order? BTW I was being sarcastic on getting an injector from the junk yard. Ha

[silkysmoothyjud]

Alright, I am having a similar prob, but I've been down this road before...Still trying to save some cash. I have replaced 4 injectors with OEM and I think I am gonna replace the remaining 4 with D-works injectors and just be done with it. Injectors 1 and 2 can be replaced without removing the plenum, so put iffy aftermarket old ones to the front strong ones in 5-8. I am soooo done, I am just gonna replace the other four and that will be the end of it. Keep a few spares around to fool with #s 1 and 2. Make sure you pull that fuel pump fuse while your Q is running and let it die before removing, unless you like rod knock/hydrolock...