Ok so I have a 1991 z28 with a 5.0 TPI and recently the idle has been a bit rough and car feels sluggish. I just recently changed the spark plugs and fuel filter but that didn't help at all. So I decided to ohm the fuel injectors and got a reading as follows
1 2 3 4
Front of Car INTAKE/RUNNERS Rear of Car
5 6 7 8

Injectors Ohms
1 11.9
2 11.9
3 17.0
4 16.8
5 08.0
6 17.0
7 17.0
8 17.0

Please let me know which ones are bad and which injectors are good. Thanks

 

They are all bad, just replace them as a set. See Southbay Injectors, a sponsor here.

RBob.

 

Ok thanks I appreciate it. If you don't mind me asking what is the normal range for the injectors for future reference? Also do you know what the stock injectors are pushing 19lb or 21lb?

 

Stock 305 is 19#hr, use the promo code tuned for a 10% discount.
http://m.southbayfuelinjectors.com/p...7&product=1500
Below 12 is bad, typically a veritable of 1/2 a ohm between injectors. New coils will be 16-16.5 ohms.

 

Thanks I really appreciate the help

 

RBob,
Why are they all bad in his case? I've been struggling with a problem similar to his, and my checked 17.0 across with 2- 16.8's.
What should they read?
Mines a 5.7
I understand replacing all if they need it.

 

His car being a '91 has Multec injectors. They fail by the coils shorting out, which you can see as many are too low in resistance. By the age of them, they are all bad. Any '89 - '92 TPI or MPFI 3rd gen with the OEM Multec injectors has bad injectors.

Your '88 didn't get Multec injectors from the factory, so it is rare that you will find a shorted coil in one.

RBob.

 

Ok Then, well said and helpful.
Thanks for the explanation and info.

 

If you have 3 out of 8 acting up, you should replace them all as a set because ...

#1 - age 9as mentioned) of the ones test good are limited, going to go soon, a whole set of reman'd is about $130, do you want to tear the whole thing apart again ?

#2 - a set is (should be) tested and "balanced" meaning the flow has been measured and they disperse fuel equally (close to) old ones may OHM out good, but they may not flow good.

 

Here is a comparison to stock Multec vs Bosch III. The Bosch III are better in every way compared to the Multec. I've found that it's not mileage that does in injectors, but rather age. As my Multecs went about 3 years ago when I had about 35,000 miles on the car. It may be the ethanol that eats them. It may just be the age.

I will say that replacing with Bosch III made the car idle smoother than it did brand new. Definitely replace all of them while you're in there.

 

Wow Reid, Thanks for that video!
That explains alot, and clearly the winner here.
No Jersey, just making my list and checking it twice.
After doing my Ohm tests and checking some other things, I discovered a small nest under the plenum of a very clean car. That said off comes plenum, and in goes new injectors anyway.
Will see what else in the process too.

 

Just popped the top off today .... cleaning up the gunk.

 

Woah Reid, that's a hell of a video.
Thanks for posting. Purchased Bosch III's yesterday, even more excited for them to arrive now!

 

Got injectors, reg, and rail on. still fighting the stupid bolt that holds the bracket on where the fuel line hook to rail. The geniuses didn't make it easy.

Going to get a 3/8 x 1/2 bolt vs 3/4, bolt hits the compression fitting. Unless I undo compression fittings and bent the line ... don't want to do that.

But finding that size at HD or AutoZone ... nope - not popular size. Going to Fazzios (Mans Hdwe Store). Its holding me up from closing it up.


Question for the Veterans:
When should I test for leaks ? Put runners on semi-loose... or before...?

Should I press schaeder valve while fuel pump is priming ? Let air out...

 

Test for leaks BEFORE you assemble the intake any further than necessary.
Depressing the scheader is not neasisary as the system has a return line and will auto purge the air from the system.

 

Thanks, I did the test before runners went on, good thing - had a pinched oring on one injector, fixed it and all good now, Schrader valve is acting up, weeping gas out the middle. ? Anybody else have that happen.

 

the valve has a cone in the bottom that seats against an o ring, sounds like its worn out. Get a valve remover and take it out and check, I bet its cracked.

 

Yea, just got back from Auto zone and got a stem remover and AC system valve stem kit, has a variety of stems/cores w/o ring. I will pull the core tomorrow see whats up.