My 1986 was running good when I parked it 3mos ago, now I have a miss on 5,6,&7. I put a cap and rotor on it, even though it didn't seem bad. I have good fire at the plugs, have compression, and good fuel pressure, and the injectors all sound uniform. Still, I can't get them to fire. I can't believe that 3 injectors could fail at the same time. I would change the injectors if they weren't so difficult to get to. Do you know of a valve, or switch, or vacuum hose that would kill just three cylinders. I had it running to do some of the testing, now it doesn't want to run, may have lost another cylinder. ????

 

You need to clarify "Miss" as a "miss" to me is an occasional "skip" while running while a "dead" cylinder is ....well.... dead.

If you have a miss, I'd put some fresh gas and some injection cleaner (high concentration) and run the snot out of the car for a while.

If dead, you need to do a full on injector service.

 

IF they aren't Multec, have them cleaned and tested. Why waste money on that snake oil?

 

Check the resistance of all the injectors and see what you have.

Like aklim says, if they're Multec just chuck em

 

I guess that I meant dead. I've been following another thread, and it does sound like I'll be tearing it down for injectors. I was hoping that there was something else that would kill 5 6 &7. It's curious that they are in line in the firing order, at least in the cap. It would make me think ignition, but all that checks out ok. I was hoping that someone had run into this before, and found EGR, or mass air flow or ?????
The other thread that I've been following, the guy says that 5 6 &7 are down on his car too ....????

 

6 5 7 are in line under the firing order. Maybe some fluid was sucked up?

 

Are you thinking through the intake ? It has been setting under the carport for a couple months. It was running last week, but hardly runs at all now. It has gotten that bad that quickly. Can an intake gasket flood those cylinders, or does the water even pass through back there ?

 

Just to toss ideas out, a fluid or maybe something got sucked up into the fuel line and was enough for 3 cylinders? IDK but grasping straws.

 

Thanks, I'm going to suck it up and put some injectors in it. That's what it is looking like. I just didn't want to get ahead of myself. Everyone seems to have the same answer. Thanks again

 

Without proper testing which includes a bench test, it is really hard to know for sure. At this point, it is a SWAG. That said, seeing as they are old, they can stand to be cleaned so why not? If you get cleaned and tested injectors, they are known quantities and you can go elsewhere but without that, the next things might be much, much harder.


What we want to do is rule something out as opposed to guessing something out.

 

Might poke around with a flashlight, see if any wires broken or chewed.

Mice are Evil.

 

Wait until it is dark, open the hood and start the car. If a plug wire is broken or chewed then you will see sparks jumping from the wire(s) to the nearest ground. Replace the plug wires if you see any of this.
I you do go with new injectors then use Jon at Fuel Injector Connection. Great service and prices.
Be sure to replace those old O rings in the fuel rail too.

 

If you are going to check for spark leaks, do it I a dark garage and spray a fine water mist around the plug wires. Make it easier for you to see. Any spark leaks, replace all plug wires.

I don't know about others but I don't reuse my condoms or my buddies' condoms. Same with O-rings or paper gaskets

 

Im helping fenty as well on this same situation. i saw your post in the other thread.

here is how i would do it to avoid spending un-needed money swapping parts and avoid spending unneccesary time pulling injectors.

1. ohm test. (if they are not all more or less the same, this is an immediate knock out blow and you need to get new ones) note, as Ak reminds us, good ohm does not meat they cannot be plugged or partially plugged so passing the ohm test on its own will not veryify if they are good.

if pass then
2. listen to the injector click click click click with a stethescope or long flat blade screwdriver, put the handle end right into your ear. the ticking nose should be the same across the board. Here is an example of having one quiet injector: https://www.corvetteforum.com/forums...-injector.html

if all your injectors are ticking along, it still does not rule out a clogged injector.

3. next you have to verify spark. pull your spark plug on the "dead" cylinders and on the closest "good" cylinder. unplug the fuel pump fuses and the injector fuses. now get somebody to crank the car and hold the sparkplugs boots in your hand and compare the two different spark qualities. Again, as Ak always reminds us, make sure the spark is loud, snappy, and whitish bluish. If not, then you have a problem in your dizz, or plugs themselves, or plug wires.you might want to set the spark plugs on a tire or a piece of rubber. You might get zapped if you are holding the boot.

I realize you said you did the cap and rotor but that doesn't mean anything if your pickup or ignition modlue or coil or grounds in the cap are gone.

If everything looks good so far, then you most likely either have no compression in 3 cylinders (highly unlikely right??) or you have clogged/seized injectors.

But because I don't like tearing down the TPI intake if I don't have to, grab your compression testor and test compression. if you get one or two values lower than others, then you need to squirt oil into those spark plug holes and then try again. if the second cmpression run after you have squirted oil into the spark plug hole goes higher, then you have worn rings and you will likely want to stop and evaluate the future of the car. If the compression is unchanged then you will have a valve seat job to do.

If compression is good all the way around (within 15lbs of each other) then we have one thing left in this case:

4. clogged injectors. you will need to tear down the TPI intake, if it is your first time, then bag and tag using clear sandwhich bags and write on a sharpie details of the bags contents. pull the injectors out and if they are multecs, replace with new from Jon and FIC. IF they are not multecs, you can clean them yourself, this worked for me but I know that others will say for the $$$ just get new ones. At my location they cost $600 landed to me so I chose to attempt to clean mine myself and it worked fine. That said, I did not have a major occlusion problem. My method may not work if they are really really clogged, and my method will definately not work if they are occluded with solid particulate. That said, you can observe the spray pattern using my method and you will know if they are brutally clogged or not. In my case the spray pattern was "matched". I am not saying be cheap, but just if you are in a pinch for $$ you CAN do it yourself.

Or just buy new ones and go for it. If you have a plugged injector that is so bad it can't fire, you WILL see a major difference in those spray patterns using this method.

5. If you find that your spray pattern is the same.....or...if you replace the injectors and find that our still have the miss....then i don't know. I think we would have to look at wiped cams, that sort of thing.



I wasted a heap of $$ replacing parts that turned out to be good. I've become a master of diagnosis now. Saves me a heap of time and $$. Good luck with it.

 

wth are condoms

 

The things that you give to your 12 year old kids so you don't have to be a grandfather and babysitter. To prevent most of the fawking hr/she gets for the fawking he/she gave.

 

>>>if it is your first time, then bag and tag using clear sandwhich bags and write on a sharpie details of the bags contents.<<<

Good advice but I'd go one better and use masking tape on the bags to mark the contents. On my builds seems if I handle the parts bags more than once the Sharpie notations go "poof".

later, tiny

 

Are the plugs dry on those cylinders? If they are wet at all injectors may only be a part of the issue.

 

Thanks for all that, but the mystery is unfolding ( I think ). Like I said, there wasn't anything wrong when I parked it, so there shouldn't be anything seriously wrong now. Things need to make sense..... WELL, I pulled the injectors, and while the fuel line was leaking out, the gas seemed weak. Turns out it was water !!!!! It turns out that we've had things blooming, and some of that stuff accumulated in the fuel tank well, and plugged up the drain. The water was standing above the filler cap. I don't think that the cap was sealing well enough to keep the water out. I have new injectors coming, but the old ones ohm good, 16.8. I haven't checked the spray pattern, but am going to replace them anyway. The problem now is how to get the water out without pulling the tank off. ??? Do you think that if I pull the filter, and run the fuel pump, that it will get enough out that dry gas will take care of the rest ? The water will be at the bottom, and I don't expect that there is much in it now. I let it drain, and didn't seem to be getting anymore water after a couple gallons. Another thing, is the cold start suppose to ohm the same as the injectors ? Mine is 4.5... Thanks for all the help, you guys are great

 

Who knows? You let it sit and you could have condensation.

Don't care what it ohms out at since you are replacing it.

WGAS. Dump the fuel. Take the pump out since it is stupid easy. Suck out the gas out, let it sit in the tank for a bit and pour most of it out and set fire to the rest. The old gas you can use in your neighbor's lawnmower, set your neighbor's yard on fire or whatever. That is about all it is good for. With the gas out, you can use a dry rag and soak up anything left. Let it dry for a day and check again. If it is dry, dump 2 gallons of fresh gas in in and let it sit. Suck it up again and this time you can reuse the washing gas in your lawnmower safely.

Who cares? Let Jon take care of it. He can service that one and send you new O-rings. Now you have a complete set. Another option is for longer crank times and you block it off or you can also block it off and have someone increase the pulse width during crank. 3 options.