Alright, my cars running rich and I can feel it miss between idle and 1500rpm. The 305 TPI has new plugs, wires, o2 sensor.

So I pull the plugs and 3 of them have black tips. The rest are white. So I start the car and pull the wires from the distributor one by one. Sure enough, I can feel an RPM drop in all but the 3 cylinders with the black tipped pluggs.

So now I'm trying to look at the injectors. I used a test light and verified that each is getting an electrical signal. I bought a fuel guage and the fuel rails are at 44psi with the key on, and holds steady.

So my question is 'what next'? How do I test each injector with a voltmeter nad/or fuel guage? The injectors have two wires. Where do I test the resistence at? I unplug the connector and test between the two contacts, but it shows 0 ohms.

The injectors on those 3 cylinders 'click' just like the rest.

I'd appreciate any guidence...

also, is there any harm in leaving the fuel guage attached. Can I just hook it up to something and leave it? It looks pretty cool.

thanks

 

It is very possible that you have some leaking injectors. Leaving the fuel pressure gauge on...run the engine. Turn the engine off. How quickly does the pressure drop, and by how much?

 

It may not be fuel related. run a compression check and leak down test on all 8 cyl. if those are all good then look at fuel, i.e. injectors.

 

The fuel pressure drops 9 psi in 25 minutes after I shut off the car. It drops to 0 psi if left over night.

Is this normal? or leaky injectors?

 

I think your fuel pressure drop is normal. About what mine does. I think you need to look elsewhere. You could have some bad gaskets, causing oil to get into those 3 "black" cylinders. I would start with that compression test as mentioned above.

 

Did you put new plugs back in those 3 cylinders when you went to test it? The old plugs are probably oil fouled so of course those cylinders are going to be missing, fuel or no fuel, if you put them back in. If you haven't already try it with some new plugs and as said earlier, do a compression/leak-down check of those cylinders. You might have a few bad valve seals or excessive blow by (worn rings) which would explain the black deposits all over the plug.

 

When you say you ran your ohm meter from the two contacts, do you mean on the wiring or on the injector? you should be testing the leads on the injector, and the resistence should be between 12-16ohms, and they should be all approximately the same resistence. BTW if you're getting no resistence I would imagine either your meter is broken or the injector is shorted out.

 

I did run the ohm meter between the 2 contacts on one of the injectors. I'll take a look at the meter and test the other injectors if works ok.

Another thing I just found out is that i'm getting only 13mpg. It used to be 18-20mph last year. I drive alot on the expressway. Also, I failed emissions with excessive HydroCarbons.

This is whats causing me to look at the fuel delivery. Cause my car has over 135k on it, and I put in a quart of oil almost every week. So I know all kinds of things are worn in that engine. I just dont have the time or a garage to rebuild/swap the motor...and I don't have the money to pay someone else to do it.

But I like my car and i ain't sellin it...yet. So whatever I can do to squeeze a few more years out of it.....

And I have not replaced those black-tipped plugs, cause they were less than a month old.

thanks

 

Ok, First, if your car ONLY has 135k miles then its just broken in. A fairly recent SBC should at least last to 200,000 if its not beaten severely and if you care for it correctly. If you're really worried about the engine, if you fear its worn beyond servicability get a compression tester and test all the cylinders for compression and run a leakdown test. Specs I believe are listed in the Chiltons manuals and the GM shop manuals.

Second, if you have fouled plugs what makes you think anything is goign to improve? If they're fouled, they won't be firing enough to burn the fuel efficiently. What plugs are you running? You may want to look into a platinum plug as they're less likely to get fouled. Not to mention they last virtually forever and Bosch Plats are cheap.

If your injectors don't test within spec, don't bother trying over the counter injector cleaners, send them off to be cleaned and flowtested. Do a search to find details.

 

yea.....i'm using bosh platinum.

I'm gonna go buy a compression guage this week.
I'll be back with the results...