CarAteMyMoney

Is there any kind of scientific way to test for a leaking injector on a TPI engine?

91Z28-350

Yes, it's called the injector balance test. The injector balance test checks the injector in the car. You disconnect the injector harness from all the injectors, hook up a fuel pressure gauge, and use this injector testor which hooks up to an injector (in place of the harness) and you fire off the injector at your control. You measure the pressure before and after, repeat for all injectors. If one or more injector is bad, it's variance will be more then 10kPa compared to the other injectors.

Before you do that, check the injector resistance first. It'll probably be much faster to do that.

joker37

One of the ways i read about in one of the Automotive repair manuels was to pull the fuel rails, and put a peice of paper under each injector, then turn the key to prime the fuel pump. Any injectors leaking will drip gas onto the paper, and *bam* you have your leaky injectors. Its probably a good idea to take all the proper percautions when working around the fuel system. Just had to mention that for safty.

Laters,

Joker

rezinn

I don't see how an "injector balance test" is going to tell you anything other than that you've got injectors leaking. You fire off an injector and the pressure drops a certain amount based on how much it's fired, but if you've got injectors leaking it's been dropping ever since there was fuel in the rails. Pressure will bleed off no matter what if you've got a bad injector, so doing this won't at all let you isolate the problem. Pulling the fuel rail and priming the pump to watch for a drip seems easier and more reliable.

Svelte_SS

Is there an easier way to get the retaining clips off and on the injector harnesses? It took me forever to access and test and re-clip the easiest one. I can't even imagine getting at the buried ones...

91Z28-350

If you already know you have leaking injectors, why do the test? The test is to find out if you've got bad injectors. That along with the resistance test will suffice. If you're leaking and you know you're leaking, just replace it. Pulling the fuel rail is quite a bit of work just to see if the injectors are a problem. You've got to pull the plenum and runners and clean all the gaskets, replacing the gaskets, and most likely the o-rings too. You might as well just replace the injectors if you're doing all that already. Sure, it's fault proof to prime injectors and watching if it drips, but the point is to diagnose so you don't have to pull the injectors to see if it's leaking.

Like I said, check the injector resistance first. Hook up an ohmmeter to the 2 nodes of the electrical connector of the injector. Depending on the injector, the resistances are usually 12 or 15-16 ohms for GM injectors. The resistances should be matched within a small variance. To determine your injector resistance, use a dental mirror, wipe off the top sides of the injector and look for the imprint, and search for the injector stats.

If the resistance is OK, then try the injector balance test.

91Z28-350

Use pliers, squeeze the clips in and lift up. Fingers can get in the way in the tight area.

CarAteMyMoney

The resistance is all correct, yet I still get a rough idle, jerky throttle response, and horrible gas mileage

91Z28-350

Can you give a better description of your problem?

CarAteMyMoney

OK, the TPS, IAC etc is all set right.. new O2.. the problem is even with everything set properly I still get a bit of a rough idle and horrible gas mileage. Throttle response is a little jerky, and when I leave the car in the garage it smells like fuel later on

I get about 12-14mpg overall when others have seen 5+ mpg more

When I got the car it wasn't running close to how it should, and it feels like i've almost got it there, but not quite...

OH yeah, I don't know if it's the scanner or what but when I hook the scanner up and plug in any variable, like 02 voltage, it refreshes the number like once every 3 seconds.. on my other tpi cars it used to update the number a few times a second

KC10Chief

Just curious, roughly how much does one injector cost? Matt

Ed Maher

For something that bad, i doubt your problem is as simple as a leaky injector.

bnoon

I just replaced all of my vacuum hoses hoping that I wouldn't have to pull the injectors for just about the same issue RE: poor MPG. I gained 1-2 MPG back, but everything else is good up to this point. I've changed the O2, checked for gasket leaks, etc. Looks like the only thing left is the injectors themselves.

My injectors check out fine electrically. That means a good cleaning *should* clear them up if the internal seals aren't worn to badly. I'll be using the DIY method posted by a thirdgen.org member here a while back.

rezinn

I see. That seems like a lot of work to just see that you've got an injector leaking. Why don't you just pinch off the return line, prime the pump, and check to see if pressure drops? That will take maybe five minutes.


As far as your problem, it may be a combination of things. Leaking injectors could very well contribute. See any gas puddles under the car? If you drive with a lead foot, 14mpg may be good for you.

91Z28-350

Yes, that's true. Pinching off would work, though I've not done that. How do you pinch it off? Remove the return fuel line and cap it, or just put a clamp on the rubber return hose? I kind of need to do this particular test, because I just noticed my fuel pump priming and awfully lot when I had to toggle ignition switch for some work I was doing. I hooked up my fuel guage and it doesn't maintain pressure. I don't think I have a fuel leak, no smells, no droplets, and I don't think my injectors are bad. The drop is very fast, and seems too fast for a leaky injector and a smooth running injector. It seems like my fuel pump check valve may be shot, so I need to check that.

GM injectors are worth something, as they aren't exactly cheap from the dealer. Finding the bad one may be worth it, for selling the remaining good ones to someone on e-bay.

thunderstick

actually, you might not have to pull the plennum, runners, etc. if you break loose the fuel rail and start with the pass side injectors, there's barely enough room to wiggle the injectors out and remove them. the locking clips could be your biggest pain, though. do the pass side first, leaving the injectors out, do the drivers side next, removing and replacing the injectors, then go back and replace the pass side injectors. it can be done. i know.

KAM

rezinn

You won't remove the clips to pull the injectors out of the intake. You want them in the fuel rail still. You just need to remove the plenum and loosen the runners, remove some bolts and pull the injectors out. You might want to replace the o-rings, but the gaskets will be fine unless they're ancient and break, in which case they should be replaced anyhow.


You can clamp off the return line beside the drivers side accessories where it's rubber.