My 1997 Nissan Altima GLE (Engine KA24DE) misfires on cylidner 4 (P0304 code) when the EGR system is attached. When the vacuum hose to the EGR valve is disconnected, the misfire completely stops. All the EGR components test OK on the bench. The car also seems to be calling for EGR right off of idle (in the 1000-2000 rpm range) as well as during normal operation (2000-4000 rpm range).
I've performed the following work/tests on the vehicle:
Replaced intake manifold gasket (upper and lower plenum)
Replaced spark plugs, wires, distributor cap, distributor rotor
Compression tested - all cylinders at 150 PSI (+/- 2 PSI)
Tested vacuum at intake manifold - meter reads about 18" vacuum and steady - revving the engine causes vacuum to drop slightly and then come back up to normal
Swapped fuel injectors for cylinder 2 and 4 to see if the problem followed the fuel injector and it did not - misfire continued on cylinder 4 even w/cylinder 2's injector installed
Tested resistance across fuel injectors (all injectors are at 12.0 ohms +/- 0.2 ohms)
Listened to injectors - all of them seem to be tapping happily away at idle
Adjusted engine timing to 20-deg BTDC
Adjusted idle speed to 750-rpm
Since the problem seems to be related to the EGR system, I also tested the following:
EGR valve (I applied a vacuum to it and the car began to stumble at idle as it should)
EGR BPT valve (removed from the car and blew into the bottom port while checking for airflow at the top 2 ports - the BPT seemed to function properly)
EGR Solenoid valve (removed from the car and tested the valve according to the service manual - it functioned perfectly)
EGR temperature sensor (appears to function within normal resistance limits)
Checked all hoses for leaks, cracks, etc.
I have seen weak egr return spring's cause the valve to open too far causing the miss fire to happen. It will hold vacuum and all that but with a weak spring it just open's too far too fast.
March, 21, 2011 AT 9:57 PM
I have even seen bad electric egr valve do the same thing you unplug them the miss goes away you plug them back in the miss return's.
March, 22, 2011 AT 3:20 PM
Should I look to replace the BPT valve or the EGR valve first. A couple of people told me that the BPT valve is probably bad. I pulled vacuum on the EGR valve and it didn't open until at least 5" of vacuum, so I'm wondering if I should start w/the BPT.
March, 22, 2011 AT 3:20 PM
Also, do you know if the car is supposed to call for EGR directly off of idle? The misfire usually occurs at or around 1500 rpm.
March, 22, 2011 AT 6:41 PM
I posted the description and operation and testing of the bpt valve and the egr valve. The egr valve can open just off of idle as you read what I posted there are different condition's for it to open.I would test the bpt valve like it say's to I would say it's the egr valve that's bad because you said the miss goes away when the egr valve is unhooked and come's back when you hook it back up. Let me know what you find.
The EGRC-BPT valve monitors exhaust pressure to activate the diaphragm, controlling throttle body vacuum applied to the EGR valve. In other words, recirculated exhaust gas is controlled in response to positioning of the EGR valve or to engine operation.
1. Plug one of two ports of EGRC-BPT valve.
2. Vacuum from the other port and check leakage without applying any pressure from under EGR-BPT valve. Leakage should exist.
This system cuts and controls vacuum applied to the EGR valve and EVAP canister to suit engine operating conditions. This cut-and-control operation is accomplished through the ECM and the EGR valve & EVAP canister purge control solenoid valve. When the ECM detects any of the following conditions, current flows through the solenoid valve. This causes the port vacuum to be discharged into the atmosphere. The EGR valve and EVAP canister remain closed.
* Low engine coolant temperature
* Engine starting
* High-speed engine operation
* Engine idling
* Excessively high engine coolant temperature
* Mass air flow sensor malfunction
Exhaust Gas Recirculation (EGR) Valve
The EGR valve controls the amount of exhaust gas routed to the intake manifold. Vacuum is applied to the EGR valve in response to throttle valve opening. The vacuum controls the movement of a taper valve connected to the vacuum diaphragm in the EGR valve.
Apply vacuum to EGR vacuum port with a hand vacuum pump. EGR valve spring should lift.
If NO, replace EGR valve.