Fuzzman17

Well it's emissions test time again and as last time I failed. I'm looking for suggestions on tracking down the problem.
I have a 92 RS with a 305 TBI with 132,000 miles. my first test as as follows
HC 2.12 Standard .80 CO 3.70 standard 15.00 NOx 2.56 standard 2.50.
I checked the timing and it was way to far advanced. I reset the timing and cleared the trouble codes. I restarted the car and smelled the exhaust. Be fore it would make your nose burn and eyes water. now it was fine so I thought I was good. I retested and got failed on HC 2.21. Now CO is 5.80 and NOx is 2.02. I can smell gas at the tail pipe now. I have noticed a slight surge at a steady cruise and a vacuum gauge shows a fluctuation of about .75 in Hg. I can also hear the Idle change ever so slightly. this is from cold to operating temp. First test showed a vacuum of between 20 and 21 in Hg. after changing some suspect vacuum hoses it dropped to between 19 to 20. I plan on changing all the vacuum hoses but got rained out. I also noticed that I can't get the EGR valve to open using my hand vacuum pump but it does hold vacuum and I can open it manually so I need to check this out some more. I sprayed carb cleaner along the sides of the intake and the vacuum surge remained the same. Spraying the base of the throttle body did stop the surge but that could have been due to it leaking past the air cleaner and the spacer. short bursts sprayed in the cold air intake has the same effect and it lasts for a bit even after I stop spraying. Injector spray pattern seems fine on a visual inspection. MAP and Coolant temp sensors are working but I haven't checked the accuracy yet, just confirmed that they are giving readings that seem reasonable. I also need to check the fuel pressure but don't have and can't find an adapter to check it while the engine is running. Looks like I may have to make one. Engine runs fine with good power other than the surge I mentioned. Any suggestions on what else I might check?

Fuzzman17

Finely got the time to get back to it. I've checked/replaced the rest of the vacuum hoses. Tested the valve at the vapor cannister. Removed and checked the EGR valve, witch appears to be a negative back flow and found it to be working properly and not leaking. I still need to check the fuel pressure. I have to be overlooking something. Any one have any Ideas on what else I should check?

Fuzzman17

Have a little more info now. I rechecked the timing and noticed that the timing varies slightly when the engine surges. also noticed a 2 in HG fluctuation when the engine is cold. At one point the surging stopped then started up again. Could I be looking at an ignition module/coil problem not a vacuum leak?

ApolloX64

iTrader: (1)

When you checked and changed your timing did you disconnect your esc module as well and try it like that too? My module causes a rough erratic idle when plugged in.

Fuzzman17

Yes I did check it both ways. as I recall with the EST plugged it I'm running some where around 10-20 Deg. advance.
I think I have eliminated all possible vacuum leaks as the problem. The fuel pressure gauge I have only goes to 10 PSI. on a static fuel pressure test I Pegged the needle at 10 PSI.
After doing some more reading on possible causes I will check the IAT and CTS Sensors today.
I have had the ignition module tested at Advance Auto and it passed. I also did an ohms test on the coil and it seems to be okay. I say it seems to be because I can't find the specs for a GM coil but it is close to an Accel coil.
I took the car for a test drive and stressed the engine to 4500 RPM in second gear and to 3000 RPM in third (about 80 MPH) accelerating to 100 MPH. In both cases the engine ran strong with no noticeable misfires. I did notice that the exhaust did not have as strong of a gas smell when I returned. I had also ran some Seafoam through the engine before the test drive.
Cat and O2 sensor are both about 2 years old with very little mileage on them. I also cleaned and put a gasket kit in the throttle body at about the same time. It also got new plugs, cap, rotor and wires then.

ApolloX64

iTrader: (1)

Cool sounds like you're thoroughly covering your bases. I narrowed mine down to a bad pair of injectors causing my idle to be off, car runs strong same as yours. I cleaned my IAC valve last weekend, it was so gummed up that after I cleaned it I had to reset the timing because the valve had thrown it off by a ridiculous amount.

Fuzzman17

I pulled the IAC yesterday and it looked clean. I sprayed some carb cleaner in the passages and let it sit for a bit then I started the car and sprayed some more in for good measure. I checked the CTS and IAT Sensors and both checked good. Just to cover my bases I replaced the O2 sensor. The thing that puzzles me is when I first reset the timing the exhaust smelled fine. There was no odor of gas and the fumes didn't burn my nose or make my eyes water. this was not the case when I brought it back from the emissions test. I did recheck my injectors first thing this morning. one was at 1.5 ohms the other was 1.6 ohms (out of spec by 0.1). The one that tested at 1.6 was the one I had changed a couple of years ago. at that time I had also tested and set the IAC and TPS. I am going to re check both of those to see if anything has changed. I'm beginning to think it may be a fuel pressure regulator/injector problem but I want to make sure everything else is in spec first.
Thanks for the input.

Fuzzman17

I also noticed that the O2 sensor was clean when I pulled it. only a slight film of carbon on the tip.

Fuzzman17

I think I got this. I turned up the fuel pressure regulator and cleaned the ground for the ECM and it seems fine now. I'll take it tomorrow and find out, that is if my fan switch comes in.