95 Z28

Ok, here's the deal. Did some routine maintenance on the car the other weekend and then it started to have some issues.

Now sometimes when idling it will just die, quietly, just shut off. Sometimes it'll run really rough like it's only running on 4 cylinders.

And sometimes, very rarely it will have burps when driving regularly around town, like it just skipped a beat and then everything is normal.

Once I give it gas and were on the road it seems fine, except for the rare burp. Even WOT it just goes. I'm sure something's going out, just don't know what.

So most of the issues are when it's idling. I get no SES lights. I thought at first that something in the LTCC was going wrong but I've checked all that. It's firing even when it's running rough. So I'm thinking it's fuel related, possible regulator or fuel pump. I've got 202K+ on stock pump. I'm going to get a test gauge and test that as soon as I can.

But what other things can I check and rule out?

 

What kind of maintenance did you do, although your problems might be just a coincidence. Pull the vacuum hose off the regulator and see if gas dribbles out. That would mean the diaphragm is ruptured and you need a new regulator. If you can get the engine to die again, push in the schrader valve on the fuel rail and see if gas or just air comes out. But an accurate check of what may be going on with the fuel supply is to hook up a fuel pressure gauge and see what the readings are. Fuel pressure specs on a stock pump is 43.5 psi engine running with the vacuum line off, or with the engine off (no vacuum obviously). Factory pressure specs give an acceptable range of 41-47. With the engine running (with vacuum attached) pressure should drop 6-8 psi from your previous reading. Also, when you check the pressure with the engine off and vacuum connected, switch the key off and see if pressure holds, which it should, or if it drops fast. If it drops, it's either the regulator, or the pump isn't holding back pressure as it should be.

 

im still having problems with mine off and on tooo, im thinkin its the ltcc or the ltcc doesnt like the msd opti or i have a wiring issue.

 

All I did was replace a plug wire and then change the terminals at the coil ends on the rest of them. I don't think any of that is the issue. I cleaned the filter as well. Unfortunately I do think it's either the reg or the pump. I'll get a fuel pressure tester and let you know the results of that, but it's probably not going to be until later in the week or so. This car is not my priority anymore.

Craby, have you emailed Mr. Bailey and asked him about your set up and issues? I emailed him with mine a few days ago and he gave some stuff to look at. All of which looked fine so I moved on to the fuel system.

 

Ok guys, got a little testing done today and here's the results.

It's a very erratic idle after warm up, doesn't seem to do it until after it's warm.

I put a fuel pressure gauge on the fuel rails and this is what I got.

No fuel spurting from vacuum port on the fuel reg with key on or engine running.

With just the key on, I got a reading of 17 PSI 1st try. Released pressure and got 20 PSI second time. Both with vacuum hose off the reg.

Running with vacuum hose off I got 44 PSI the first time. It was still cold here.

Second time I got 34 PSI, warm. AFTER I put the vacuum hose back on.


And it started running erratic between the two readings.

I also verified that my LTCC module was receiving a constant good signal from the Optical sensor.

So now I'm thinking it's a sensor affecting the air/fuel at idle, like maybe the IAC? Is there something else I can test? What do you guru's say?


I have an older auto xray tool I can use to look at various readings. I just don't know what to look for/at on it. If you can suggest something I'll plug it in and take a look.

 

The fuel pressure should have dropped when you reconnected the vacuum hose to the regulator, not gone up. Put me down for it being a bad fpr. No sign of gas in the vac hose doesn't mean the regulator is still good, but gas in the hose is a definite bad.

 

My bad, got my notes messed up. The 34 PSI running was with the hose hooked back up.

I took the hose off, put a clean piece of clear hose on the reg so I could see if any fuel came out and there was nothing.

 

 

I'll give it a try this weekend if I get time. Anything specific you think I should look at?

 

Pay attention to your upstream o2 voltages and fuel trim numbers on a scan tool. Should be able to tell you if you have an air/fuel issue and you can go from there.