While trying to just see if a somewhat less than perfect but good running engine had any injector issues (92 LT1, 140K miles) yesterday I turned it into a very bad almost not-running engine in the process.

One by one (engine not running!) I removed injector wires and tested ohm reading across the two connectors on each one, seeing if they were consistent (read elsewhere should be around 12-13). Well mine all read a consistent 18 however so that threw me, and one seemed a bit low, hung around 15 (right rear cyl).

However, when I started the car, suddenly very rough idle and while it runs, it's definitely dropped a cylinder if not two, I mean it's ROUGH.

I did not miswire, I did one at a time. I did not break or damage anything I could see. I do recall - I think - seeing a tiny spark once when testing one. But with the wires disconnected how would that be possible? Static, or do these have a little capacitance and I maybe shorted the two pins directly with one of my probes?

I'm figuring the thing to do is first inspect closely again to see they're all seated fine, try running it; if no improvement, leave it running this time while removing and replacing the connection one at a time, see if I can determine the problem unit(s) that way, at least narrow it down.

IF that spark I think I saw is not the problem, could the wiring just be old and brittle from heat and just moving it around has damaged? What's involved if I have to replace the wiring cap? I do have the shop manuals (red full version) so I'll be looking into this there also.

NOT a happy camper. Any advice/experience very much appreciated and I'll poke around the forum for general advice re this.

 

This is a lot of hearsay (I read it, have no personal experience) so take it with a grain of well-intended salt.
I've read that the '92 is 'batch fire', that is a full bank fires all at once (4 cyl's.) and each is fed through a fuse. So you may have simply a bad fuse. Being wired this way, one bad (low resistance) injector can take out the function of an entire bank.
Furthermore, resistance should be around 16 ohms with variation of 1 or two ohms, so I've read.
I'm an EE and can tell you for sure that measuring a low value like 16 ohms requires some care to keep you fingers off of the contacts while measuring and to have a clean 'work area' including the parts being measured. And the instrument must be capable. But it's very unlikely that you damaged an injector coil by measuring its resistance.
Hope this helps.

 

Thanks for this - I wondered about the 12/13 ohm, I read it in a post here, I'll have to see if I can find the spec in the manuals. Mine all read around 18 like I said, one did seem lowish at 15.

But your point about the tools, etc is well taken; I used an inexpensive meter and while the contacts on the injectors certainly looked uniformly clean and bright, my probes probably have finger oil etc on them. I noticed when I moved them around the readout varied - how much surface is contacting would affect ohms right, since that's a measure of resistance? I am NO EE but not ignorant of the basics (well except that I have now screwed up a perfectly good running engine).

I'm going to check the manual for tips, look for correct specs and troubleshooting, the bank firing/fuse thing you mention, reinspect my work, look for anything broken or lose, and if not better, go through them with it running.

No problem pulling them off while it runs, right?

 

are you sure that the terminals and connectors are not corroded? Could be the injector fuse on 1 bank. Also, the ohm readings are too high. They should be 15-16 range.. Check that ohm meter again. It can't be nothing major.

 

duh, somehow one popped off, I had a 7 cylinder LT1 going there. Not going too great I might add.

I'm going back to retest though, I did get 18 pretty consistently but one low around 15. Maybe it's a cheesy meter.

They look fine, no crud on the contacts, shiny and silver!

thanks all

 

Any meter needs to be tested to see if it is calibrated accurately. Try to locate a 15 or 16 ohm resistor, 1% or better, metal or carbon film. Alternatively buy several 5%ers and measure them all. You can expect them to be pretty accurate, and even if off 5% that would be less than an ohm.

 

never thought of that, thanks, sure i can get my hands on a resistor, will do. But still - whatever the reading, it will be consistently wrong. So if my readings on one or two injectors are significantly lower than others, that indicates trouble I'd think.

But I'll get on that - much appreciated good advice!

 

Analog or digital meter? Analog has to be adjusted to ZERO the meter.

And I have heard someone was trying to check the pigtail contacts instead of the injector.

 

that's what I've got and reliable info (FICINJECTORS here) is they should be 16. It's a digital meter, they all tested more like 18 but.. old batteries maybe, not used it in ages, etc. I've been given good advice to test with a resistor then I'll know what's what before the next test. Yes I did test the injector itself not the pigtail lead but that's a good tip, you can't be too careful when passing along info and assuming people 'get it'.

thanks all!