Super_GTA

I have an 89 Trans Am GTA with a 350 and a 5-speed, still using the 305 computer and chip. I have removed all of the smog equipment except the egr valve. The car has an afpr, all new sensors, and a new iac. The problem I'm having feels like a slight miss at idle. The car is running on all cylinders. The distributor is new, after having broken a couple teeth on the reluctor wheel. I connected a vacuum pump to the egr and applied vacuum. Nothing changed. From what I understand, the engine should stall. I've also disconnected the vacuum line from the egr and plugged it. I drove the car around a bit and noticed no change at all. The car didn't throw any codes either. I've been told that if the egr isn't allowing exhaust into the intake, it will ping while cruising because of the high combustion temps. I have a 180 thermostat. I don't think the engine is pinging, but I haven't heard pinging, so I don't know for sure. Does this sound like an egr problem? If so, can I remove the valve and install a block-off plate if I keep the engine temperature down? I will be tearing the intake down soon to play with the egr a bit more. Thanks for your help.

Danno

You caught me at a good time. I just took my 89 rock for inspection and it failed horribly in the NO test. I pulled my GM manual and looked at the flow chart for troubleshooting EGR. First test, engine and key off apply around 10in of vacuum directly to the valve. It should hold vacuum for at least 20 sec or more and the diaphragm should move. As soon as you start the car the vacuum should immediately drop. If OK, turn on ignition and ground the diagnostic terminal, remove both the lines at the EGR solenoid and connect the vacuum pump to the manifold side of the solenoid valve. Apply again about 10in of vacuum and it should hold vacuum. That tells you the valve in the solenoid and the solenoid is working. If not, unplug the connector and repeat with key on diagnostic connector grounded measure across the wires for voltage. If OK the ECM driver and ECM is OK. Then the solenoid is bad. Here is the kicker. THERE IS A FILTER IN THE SOLENOID THAT SHOULD BE REPLACED EVERY 30K MILES. Damned if I knew. It's purpose is to remove vapors that can come from the manifold feed, go through the valve/solenoid assy and contaminate the solenoid valve and EGR valve diaphragm. If it get's plugged it reduces vacuum to the EGR valve. Applying vacuum to the EGR valve directly will give the slightest idle change but the engine will not change much since the vacuum won't hold because of design(I won't get too lengthy). The car will run better without the EGR from a technical standpoint since there is no dilution of the F/A mixture from inert exhaust gas, but combustion temp will go up. Fuel delivery mapping I believe is different from the 305 to the 350 unless you changed the calibrator. That could be the rough idle.

ShiftyCapone

iTrader: (7)

There is your problem right there. Your car is horribly out of tune. Did you use a 350 knock sensor, and injectors? The parameters in the chip are set for a motor with 45 less cubes that has different fueling, spark and VE settings. The solution to this would be using the correct PROM or re-burning your current one.

rgarcia63

That is a Positive Back Pressure EGR valve, it has an internal valve that can only be opened with positive back pressure, which you don't have at idle.
Follow Danno's instructions to test.

The EGR valve is used to lower NOx emissions by reducing combustion chamber temps. Without EG the rise in delta T isn't enough to cause pinging. The engine shouldn't ping whether it has EGR, or not.

brutalform

If you remove the EGR, and block it off with a plate, the ECM is still going to look for the EGR. You would have to get into the prom to properly delete it out.