90 wont pass smog

[TonyTZR1]

Well, the dreaded SMOG issue. The car passes everything but the idle test. The idle fluctuates up and down, even more so when the secondary injectors are on. Is this a result of an injector/injectors leaking down?

Thanks;

Tony

Need to check fuel air and spark.

More than likely you have a couple of injectors petering out.

[TonyTZR1]

Thanks for the feedback, I have just acquired the car and in the process of trying to get it to pass SMOG, here is what I have done so far:

Removed the injectors and had them flow tested.
Replace plugs, and found some bad smog hoses. Replaced. Also found the hose to the map sensor off.
Fresh tank of fuel and added Teckron.

Tony

[tccrab]

Check for vacuum leaks.
I had a funky idle similar to what you describe after I changed my injectors last year. Turns out I had a small vacuum leak at the funky one piece two pipe PCV connector just behind the throttle body on the drivers side of the plenum. If it's not exactly in place it will leak and cause you all kinds of grief. GM realized it was a problem because they changed it to a different connector in the following years.
Use a portable propane bottle (the one the plumber uses to solder pipes), don't light it but crack the valve and spray around the hoses while the car is idling. Where's a vacuum leak the propane will be sucked in and the idle will increase a little. The bigger the change, the bigger the leak.
What you are looking for is a small leak that will temporarily seal when the engine gets warm or if the RPM's are up and the engine vacuum is greater.
Also check the PCV hose that runs behind the plenum, it's a common fault, it degrades from engine heat and cracks.

Good luck!!!

[TonyTZR1]

Tom;

Thanks for the reply. When I had the plenum off, I did find three hoses that were bad. The manifold hose that holds the two pcv valves and the small "F" hose that goes on top of the pcv valves. Also found the MAP hos off and cracked. Replaced those and installed clamps on the MAP hose.
But, I will check for leaks again and see what I find.

One other question, I noticed some guys are using Accell injectors as a replacemnt. Is their any modification for the secondary side?

Thanks again;

Tony

[tomtom72]

Tony, I think this maybe a shot in the dark. There is a TSB over at the netreg site about idle fluctuation in closed loop. GM issued a updated PROM as a remedy for the 90 ECM's. I don't think this is your issue but it maybe worth a look if ya run out of things that are obviously n/g.


Tom

[TonyTZR1]

Tom;

Thanks for the information. The ECM was replaced by the previous owner in 2005. I don't know if the prom was a part of the replacement or not. I will check out the TSB.

Thanks again

[tomtom72]

Tony, you're welcome. I still don't think the PROM is a good bet because the TSB was not a recall. It was a remedy to customer complaints about hot idle surging & fluctuation. If the ECM was replaced by a dealer they proly talked the customer into an updated PROM if they were looking to pad the job/bill at a low cost-hi profit margin....I bought the updated one for my 90 and it only cost like $35 from GM. The ECM's don't come with PROM's, so you have to do the transplant if you swap ECM's, but you proly know that, I'm just covering all the bases. I didn't know beans about EEC systems when I bought my Z, boy o boy am I getting edjamacated... I come from the holley carb generation!

When your state does the idle test did they give you the print out of the results? If so then tell us what they were & it would help the guys analyze the issue.

Does she smell rich or lean? What was beyond the limits?

If I can do this correctly, someone posted this awhile back vis a vie smog testing so I put it in my favs because I'm so behing the curve with this stuff.
http://www.aircare.ca/index.php?repi...-causes-hc.php

I'm just not good with this stuff yet!

Tom

[Aurora40]

Originally Posted by TonyTZR1

The idle fluctuates up and down, even more so when the secondary injectors are on.

That seems odd that the secondary switch position would affect the idle?

[TonyTZR1]

Me too, from the Holley generation and yup, I am getting an education. I will have to go back tot he dealer and get the print out. Unfortunately the guy I am getting the car from brought it to the dealer for the smog test. Found three bad injectors, replaced and flow checked the rest.
I checked the idle myself, brought it up to the 2500rpm required for the smog test and after a couple of seconds, engine at normal operating temp, the idle drops down by 400 to 500 rpm then immediately goes back up to the 2500rpm.
The dealer said that one or more of the injectors could beleaking down, so I asked a folish question, actually two, if the injectors were a suapect to begin with why didn't you run a leak down on them before putting the car back together? And, did anyone pull a spark plug and check it? I didn't get an answer.
I think another thing I can check is the air control solenoid valve and the canister purge solenoid valve. I know the dealer didn't do that.
Now that I have the car in my posession, I am going to have it scanned and see what it says.

Really appreciate everyones help, what the hell is a computer? Man what a cluster.

Thanks again and I will try to get the print out.

Tony