1992 camaro RS converted to 355 TPI

car starts fine, idles great while warming up, no misfires or undue vibrations(~10:1 compression & mild cam & porting). No shortage of power or any noticeable driveability issues, spins into 3rd no problem. problem arises after it warms up, say 160-ish, it will suddenly start hunting at idle anywhere from 5-1100 rpm, usually not that drastic. then it will stop for a while, then start again, worse. If I put the a/c on it will almost die(or die) and then spike up again, but the hunting will be worse than before. pushing the brake pedal may or may not have an effect, i couldnt tell. Once it gets to the severe hunting you can notice it while driving, it will miss sometimes, (havent pushed it at that point to see the power loss, i was in traffic on the 5). this whole time the voltage guage steadily decreases with idle speed(from high idle to low), if the idle drops suddelnly so does the voltage guage with a/c on max and the car at ~160 the voltage is below 13, probably ~12.5. At no point does the ecm show that the car has entered closed loop( with aldl jumpered appropriately the ses light flashes 5/2 times a second).

Now, the belt is new, tensioner checks out, alternator is new & recently tested, battery is new. Entire charging system passed a check at pep boys. i initially assumed charging system because of the behavior of the voltage guage, but it appears that is not the case.

it sounds like 1 or 2 of the driver's side injectors may be clicking, i have yet to check them out for resistance. the noise could possibly be the pcv valve on the diriver's valve cover, but i dont even know if they can click(its not coming from within the valve cover at all, i think the reason i can hear it there is because the pcv hose runs right past the suspect injectors). the exhaust doesnt smell remarkably rich or lean, but im not expert at that. the pcv hose going to the throttle body was split on the end, i duct taped it together and then on and it doesnt seem to make any difference if i wiggle/adjust it, havent been able to find a replacement hose yet.

now i did some searching and have made a few guesses, but im still fairly far from pinpointing the cause. I dont know that a leaky injector could work fine normally and then all the sudden make the idle wack out, then be fine a few seconds later(while maintaining the same clicking cadence). after the idle troubles start the car is reluctant to restart, it seems that the battery is being drained(even though the charging system checks out), on friday when it died the battery ran out of juice on the freeway(after the 3rd restart), but that was before i replaced the belt(which was on its last legs) and the alternator. Im wondering if there could be ground problems that are preventing the alternator from charging fully, yet dissapears when they hook up the stuff they do to test the system. i still dont know why that would stop the car from entereing closed loop, unless each time the idle drops its because it just tried to go into closed loop but then failed miserably and reverted to open loop(the ses light still maintains the same rate of blinking though).

no codes either.

i have to make a ~340 mile trip starting wednesday, so yeah, im in a bit of a jam. i figure if it comes down to it i can probably just throw a bunch of money at it and it will go away mysteriously(or throw probably even more money to have a shop diagnose and maybe fix it), but im rather poor at the moment so id rather not have to do that. thanks for any help you can give!

 

I am no expert, but i would say that the reason is runs fine during start up, is because the engine is cold and it is running in open loop, giving the engine more fuel. And after the engine warms up it goes to closed loop. That is where your trouble happens. When it goes to closed loop, your engine reduces the ammount of fuel and that causes your engine to stutter a bit. and with a higher compression ratio, and a littly taller cam, your computer doesent know this and has trouble adjusting. If i was you i might put a new set of injectors on to get some decent fuel flow, and maybe an adjustable fuel regulator. and a decent cold air intake may help as well. getting more, cooler air would certinally help regardless.

The reason turning on your ac kills the engine is that it takes a lot of power to run that ac pump. as much as 20hp. and when your engine struggles for fuel and air, it doesent help to make it run and accessory that large. So back to my suggestion, maybe upgrade your fuel system as well, like injectors and adjustable fuel regulator, and you might be good.

 

went out and measured the injectors. Cold before i started the engine i got:

D(F to R)
16.9 15.5 9.9 16.4
P(F to R)
16.8 16.5 16.4 10.5

then after warming it up a bit i got:
17.0 11.3 17.0 16.5
17.1 15.8 14.6 7.5

ran it more until the idle started doing its thing off and on:
17.4 16.8 15.3 16.9
17.4 16.5 7.2 8.6



should i just assume that all of the four injectors that ever went below 15 are bad and replace them, or are only the warm/hot values important?

and is there any way to read the p/n of the injector without taking it out? i couldnt see any numbers from the outside.

the battery(which seemed last night like it was going out) cranked fine, so i think the starting troubles were due to flooding from when it died. Im assuming when it starts freaking out and missing that a lot of that unburnt fuel is gonna hang around in the cylinder for a while. I guess i just have to pull the intake and stuff tonight and get the right injectors tomorrow, hopefully thats all that is going on. if there was a problem with the fuel filter or something i would notice it at high rpms/loads and not idle right?, so there shouldnt be anything there.

 

I would personally assume that you didn't get a good measurment on at least some of the checks. If you have bad injectors, they will reveal themselves when the car is cold as well. Resistance should increase when it gets hot.

 

right, i have been assuming that some of the checks werent perfect, but its usually pretty hard to get a false low reading when checking for resistance(without going absurdly low) since most things that could be in the injector plugs arent conductive themselves, and if the two test prongs touch it pretty much goes to 0 instantly. i would think most(all?) innacuracies would be on the high side because of imperfect contact with the prongs.

resistance does increase with temperature for metals, but im not sure how the injector's resistance is made(if its internally determined based on arrangements of parts that could move/expand/contract from external forces, or if its just a resistor wired into the circuit). i figure if the resistance lowering drastically is a sign of injector failure(which is the whole point of checking it, right?) then the resistance must be determined by the internal structure of the injector and not just an inline resistor.

hell, ill probably go out and make a few more measurements before i shell out the time & money.