Yes indeed. A good diagnostician could/should verify the control is functioning before condemning the compressor but there seems to be some best guessing that happens. In the end, as you say, you needed all of it.
I can count on one hand the number of times I brought one of my vehicles in for service versus DIY repairs. One time, in a moment of weakness and desperation because I had no time, I decided to bring my truck in to have the fuel pump replaced. I was pretty sure that was what was wrong based on the symptoms. But, like we preach here, I didn’t tell them what to do, just relayed the symptoms.
Not hearing anything back by late in the afternoon, I called them to inquire on status. They had an entire laundry list of things it “needed” to fix the problem. They had the distributor out, the ignition module, wires, fuel filter…the list went on and I’m like whoa! Did you check the fuel pressure? Not yet. I had the service manual, it is literally one of the first steps in the diagnostic tree based on the symptoms. I told them to put it back together, I’m coming to pick it up. That was followed by a whole host of reasons why that would be impossible. I’ll be there in an hour and a half, it better be back together. It was and I paid their inflated diagnostic fee. I figured it was short money to rescue my truck.
Replaced the fuel pump myself and it was fine after that. Ran for many years after without the “desperately needed items” they were adamant had to be replaced. I can only imagine the repair bill once they were done. The last item was sure to be the fuel pump…
Of course not all shops are like this but it can get expensive finding one that isn’t.
For some reason this egr problem you had is making me frustrated … lol … Since a new EGR valve didn’t do the trick, I wonder what the actual problem was? If the EGR valve doesn’t work on my pre-OBD truck, that problem would go unnoticed if not checked as part of routine maintenance. I test it by applying manual vacuum to EGR to make sure that stalls the idling engine. That test at least verifies the valve is still working and the passages are open, but there could still be a problem with it vacuum control system. The OBD 1 Corolla, the computer reads a temperature sensor when it thinks the EGR should be open, , so it tests the valve, passages, & the vacuum control.
I just assume the problem was clogged pipes. The dealer did what said they could get at but couldn’t do a full cleaning without pulling the trans to get at all the orifices. This was the norstar engine so complex.
I don’t remember anymore if it would stumble on start up and then the check engine light would come on or if it started to stumble after the light came on. At any rate I just unplugged the egr valve and it ran fine without it. I just would have the check engine light on all the time.
Yeah, you’d get a ticket here in Calif if that was noticed.
That symptom seems more like the egr valve was being commanded to open or sticking open when the engine operating parameters said it should be closed. I wouldn’t expect clogged EGR passages to cause that symptom, other than inside the valve itself. But you proved it wasn’t the valve when you replaced it w/a new one.
hmm… If you removed the hose for the EGR’s vacuum control, the problem must have been before that in the command chain; something in the vacuum modulator function. If that was an electrical connector, it might have been the PCM’s electrical output signal to dump all the vacuum controlling the EGR valve. With no vacuum input, the EGR valve would never open, so never cause any stumbling. Another possibility is the electrical connector allowed the PCM to monitor the EGR temperature, which it would use to decide if the valve was open or not. The only other thing I can think of if that particular EGR valve design could be controlled by an electrical solenoid via a PCM output signal, and the PCM was commanding the valve to open when it shouldn’t. The EGR is usually prevented from opening at idle, colder coolant temperatures, or when the gas pedal is floored. It’s a frustrating, bewildering puzzle indeed.
Case closed. The car has been junked for years. Neither the shop or the dealer could solve the issue so I gave up with no reason to spend more money on it. I refuse to pull out my old shop manual again to study the issue.
It was only to illustrate a meeting of the minds between customer and mechanic to take a shot with no retribution.
95 olds aurora, v8,norstar engine, with the autobahn package. Black. Top speed who knows but with the autobahn package the computer wouldn’t shut it down at 120.
That is one year older than my Stratus, I should take better care of my car.
I had a P0401 fault; EGR insufficient flow, thanks to one of those feared monitors. I disassembled the back pressure transducer, found carbon particles and a tear in the diaphragm. I cleaned the diaphragm and put a dab of sealant on the tear as a temporary measure, ten years have passed by.
Like I said it’s been gone for years. One of the problems was it was changeover time for obd2 so it didn’t have all of the code functions of obd2. But I have no idea what it was you did.
I’m guessing the 94 Status EGR system is a similar design to my slightly earlier vintage Corolla. It’s pretty complicated so hold on to your hat, but I’ll try to explain how it works to my understanding.
The EGR system consists of four basic parts:
The EGR valve itself
An EGR modulator
An EGR-disable solenoid valve
A thermistor to measure the temperature of the EGR passageway
The system’s primary objective is to re-route a small amount of the exhaust gas back into the intake manifold. Done to decrease the combustion chamber temperature. The two primary benefits are (1) to prevent internal engine parts from being damaged by overheating; and (2) to decrease nitrogen-compound pollutants. The amount of EGR needed is determined by
coolant temperature, no EGR needed when coolant is cold, done via disable solenoid.
exhaust pressure, more EGR is needed with more exhaust pressure, b/c more exhaust pressure means the internal engine parts may start overheating
throttle valve position, no EGR is applied at idle or when the throttle is wide open. EGR will cause the engine to stumble or stall at idle. Wide open throttle means the driver is asking for all the engine power available, and applying EGR then would decrease the engine power. No EGR is guaranteed by the computer over-riding the modulator with the EGR-disable solenoid.
The EGR valve is what provides the physical path from the exhaust stream to the intake manifold. The amount the valve is open is controlled by a vacuum signal input . The EGR modulator’s output is the vacuum signal which goes to the EGR valve’s vacuum input. The EGR operation isn’t binary, either on or off. Instead it is usually either off or just partially on. The %-on factor is determined by the EGR modulator. The EGR modulator contains a flexible diaphragm connecting directly to the engine’s exhaust stream. When the exhaust stream is strong, the diaphragm flexes, which, via internal linkages inside the modulator, causes its vacuum output to be greater, which in turns opens the EGR valve a little more. If the diaphragm tears, this all doesn’t happen, and the EGR valve is closed when it should be open. The computer knows many of the operating conditions when the EGR should be at least slightly open. When the EGR passageway temperature (the thermistor) is colder than it should be, that causes the computer to think there’s not enough EGR flow and something is amiss. So the computer posts a diagnostic code, warning light.
@Nevada_545 's Stratus computer apparently determined the EGR passageway temperature wasn’t rising like it should when it thought the EGR valve was open. The cause was determined by visual inspection; i.e. the EGR modulator’s diaphragm had torn. This prevented the modulator from working correctly. It failed to output the correct vacuum signal to open the EGR valve.
My guess, your Old’s problem was either a faulty modulator, faulty thermistor, faulty coolant temp sensor, or faulty EGR-disable solenoid.
