I didn't get the fuel pressure checked today, but did get the injectors removed from the wrecked '02 SL-1. I also changed the AC compressor, installing on the '01, the compressor from the '02 due to the '01's nearly static pressure readings indicating poor compression and poor suction. The idle air control on the 'O2 was damaged from the crash, so I didn't bother with the throttle .body

Surprisingly the idle has been fine all day today (due to warmer ambient outside temperature?)

When the fuel pump was changed, I watched the mechanic check the fuel filter, and he said it was not plugged at all.

Tomorrow morning I hope to clean and install the injectors to try to get rid of the PO172 code. And then maybe charge the AC system In the afternoon.

Thanks again for being a sounding board that talks back with wisdom, good sense, and experience.

if you don't have other plans, my church has four online service opportunities for Easter. Please see newspring.org

 

I installed the injectors from the '02 Saturn into this '01 and it started and ran well at first, but after it warmed up the fast idle was back, at least 2K RPM, but after bringing the car to a full stop, the idle would slowly (about 5 seconds) come down to normal around 800-900 RPM, very annoying! That sounds to me like a sticking idle air control! I will try to remove the IAC and clean it soon.

I had left the battery disconnected for at least six hours while changing the injectors, so the service engine light was not on as I started to run an errand.

After I had driven the car for about an hour, it seemed to momentarily miss or choke down and immediately the "Service Engine soon" light came on. After that unexplained hiccup, the idle was normal for the rest of the evening!

This time, Autozone's scanner revealed the PO 172 again, and added for the first time a PO 507. Autozone's diagnostic sheet said it likely needs a new O2 sensor! I don't think so, after installing three new ones recently already!

Since the fast idle phenomena has been so inconsistent, it's hard to imagine it being a leaking gasket or other vacuum leak, which you would think would be consistent. I'm thinking about going ahead and spending the $40 on the Idle Air Control and see if that makes both codes go away, which would be wonderful, but that seems unrealistic to hope for. Before I do that though I will try to check the fuel pressure and clean the IAC.

Since changing the injectors didn't help anything, I don't think it would be honest to return the reman injectors as defective, so I'll probably own them as a spare set.

My confidence in the quality of Saturn products has been shaken by all this time spent chasing a problem so elusive!

 

I have almost 500K on a pair of Turds 95 and 97 SC2. They have been through blizzards, clipped the rails of bridges, run at 105 mph past Wisconsin State Prisons in Wisconsin farmland. swallowed salt bt the pound in Jersey, survived a multiple D battery attack in downtown Philly, trashed shifter bushings like all other 5spd s cars. Both are on second engines. Just redid the fuel pump on the 95 -- the original. Technically didn't fail.

For a grand total 12,600 + 14400 = 27K off the lot (plus financing) + 10 brake jobs, 22 gallons of oil, some coolant and a R134a here and here, and suspension refreshes and tires, I think I got my money's worth out of both of these in about 2005. This ain't nothing.

Some came off the line lemons -- that happens, but the ones that didn't that were reasonably maintained -- those are the ones still on the road -- that is the beauty of Saturn engineering.
Sometimes it takes a few iterations but we will figure this out.

 

Now that I know we are talking 2K dropping to idle and not hung at 4K at a stop -- have you checked the ECTS for resistance and corrosion on the connector socket or pins oF the ECTS?
Measure the resistance at ambient and operating temps and report back.
Also check the wiring, especially where the wiring feeds through the connector to the pin sockets. A lot of fatigue partial breaks. The resistance at operating temp should be on the order of 250-400 Ohms I believe.

For reference, open circuit or greater than 2500 ohms I believe tells the PCM to set the mix for -40 ambient. Indefinitely.

See if you can get the Autozone dude to check the coolant temp sensor reading for you. thermostat begins opening 185 195 so if you're sitting on -40 that is likely the issue.
DO NOT buy an AUTOZONE ECTS

It is not common for an ECTS failure ALONE to skew the mix so horrendously to throw a rich code.

An open circuit ECTS usually causes starting issues and other assorted nonsense. You haven't mentioned any so I waited until you finished your current troubleshooting steps.
The intermittent nature may be due to a partially broken wire in the ECTS circuit. Change in resistance = change in coolant temp as far as the PCM is concerned

Please check the fuel pressure. Loan a tool at Autozone is free w a deposit.....

 

I started today by soldering on longer lead wires of a little greater Gage for the ECTS, so I can check the resistance easier. When I checked the resistance this morning the sensor was apparently open on the 400 ohm setting of the meter: no reading. Same thing when I got to the auto store and the engine was more warmed up. No reading. The dash temperature gage was acting normally both times and has all along, so it didn't make sense, but I bought a new ECTS of the Wells brand anyway.

I checked the resistance reading directly on the new ECTS before purchasing it and it showed somewhere between one and two ohms. I installed it, figuring if it proves to be bad I can return it and get another one. I've been doing that a lot lately with various parts.

As on many other nights, I left the battery disconnected last night so as to erase the codes on the PCM. I headed for the salvage yard to get some parts from my wrecked car that I need to make my AC system work, the fast idle was back for just a short time this morning with some unexplained pulsations, missing, or rough engine running that finally went away and the car has run perfectly today since morning with temps reaching nearly 80°. I have enjoyed seeing it idling properly, having good power etc. just like it has on previous days in between other tantrums that it has thrown.

I was leaving the Salvage yard after driving about 10 miles total when the service engine light came back on, I stopped at AutoZone and the PO 172 is back, even though it's not welcome!

next I headed to another AutoZone to borrow their fuel pressure diagnostic gauge, but couldn't get it to function properly showing no pressure. Same story at an O'Reilly store. Finally at a another Autozone with the help of an experienced employee who has his own fuel pressure gauge at home, it did show a pressure of 91 psi both without the engine running Key on, and with the engine running, same pressure.

For kicks, this morning I put an old O2 sensor from my 'O2 car into the '01 knowing that that O2 sensor never tossed a single code before the crash, but the PO 172 came back anyway!

The last AutoZone employee asked if I thought the fuel filter could be part of the problem of such a so slow pressure buildup for starting, like is there a check valve in that filter? I told him I don't know, but the mechanic who installed the new fuel pump said that there was no restriction in that filter so he didn't replace it.

I'm still baffled by all this, willing to admit my ignorance of the possible reasons for this kind of Automotive behavior, and frustration that I have to continue to do this kind of work on the car when I have so many other things I need to do, again not a confidence builder in the Saturn brand, even though I've had good service out of about four other Saturns.

 

Fuel pressure specs

Pump pressure: 65-94 psi OK there

System pressure at idle: 40-55 psi. Uh oh

I would confirm that reading at idle.

If true, the fuel pressure regulator may have gone bad inside the fuel filter assembly.
Remember that under normal conditions the regulator will limit the fuel pressure to something normalish and bleed off some of the pressure. Failed pressure regulator--> Same pressure at rail as at tank. NOT GOOD.

Also possible a return line from the rail or filter/reg assy to the tank is kinked or partially clogged.

At 91 psi, your injectors are initially putting out twice the fuel per unit time as they should. the PCM sees this rich condition via the front O2 and tries in vain to lean out the mixture but runs out of adjustment and throws a P0172.

Definitely get the measurement at idle confirmed. Have them do only the idle measurement to make sure there is no carryover in readings.

I don't believe you have changed the fuel filter/regulator assembly. that'd be next on my list AFTER


Getting the rear left of the car on jack stands.
Put a fuel-safe collection container under the fittings where the filter regulator assy return line to the tank connects to the tank return line.
Disconnect the line using the proper release tool. 3/8"I think.
WEAR EYE PROTECTION
Have a friend turn the key to on. There should be no fuel exiting from the filter reg return line you just disconnected.
Have him crank and start the car. Be ready for a rush of gas.

Gas should be pouring out of that return line if the filter/reg assy is functioning properly -- the pressure regulator inside acts to divert a good bit of the flow AWAY from moving forwards to the engine, dropping the pressure at the rail to the range you need. The rest of the fuel is returned right back to the tank. Also, a return line at the far end of the fuel rail to return unused fuel back to the tank.

I suspect either the line is linked, clogged, or the internals of the regulator /filter assy are fubar'd. If you get no gas out of that return line, I do believe you've found your issue.



ECTS:

Do not add wiring of any type to that circuit. The PCM assumes the wiring + sensor are a predetermined resistance at any temperature.
The voltage drop across the sensor is measured to infer the coolant temperature. Sitting idling in traffic, the R of the sensor can go down to 250-300 ohms.
If you add resistance to that circuit, then the PCM thinks the coolant is not as hot as it really is. The PCM will then NOT turn on the AUX cooling fan at the right temp/time and you risk overheating.
Also, the temp gauge on the dash is rather nonlinear so it will tell you not much in situations like this.

You need only measure the resistance with the sensor installed, connector off. Two alligator clips won't fit. Two long thin probes will -- just can't have them touching -- which is why you were likely reading 1-2 ohms (meter lead resistance)

Measure the DC v drop across the ECTS connector while unhooked from the sensor. should be about 5V.

 

Just one question: How does the fuel pressure regulator know whether the engine is idling or not so that it can reduce the pressure from near 90PSI to 50 something PSI?

As far as I can tell, the fuel pressure regulator is part of the fuel filter itself for this year model. I discovered that I can spend anywhere from $244 at rock auto for a fuel pressure regulator to about $120 at one auto store in Wichita that would have to order it for me from out of town, to $19.99 at Autozone. Which of these options would you be inclined to buy? I have looked at pictures for the rock auto and AutoZone components in question, and they look identical with three ports on a fuel filter body. This tin can shaped component that filters the fuel cannot possibly be complicated enough to adjust the pressure regulation for various operating conditions.

I am not inclined to put my efforts into a repair process that makes no sense!

 

One answer.

Key on engine off. No fuel is flowing. No division of fuel between that moving forward towards the injectors and that moving through the return line to the tank. It is a static pressure built up by the fuel pump during priming, which lasts for 3 seconds after you turn the key to the on position. Turn the key and listen for a hum which ends with a click, the click being the fuel pump relay in the instrument cluster junction box on the passenger side of the bottom of the center console.

The pressure on both sides of the diaphragm inside the pressure regulator fuel filter assembly is equal. Therefore there is no diversion of fuel to the return line.. no flow no regulation because the regulation is based on reduced volume which reduces pressure.

Key on engine on. The fuel pump is engaged constantly or possibly on a partial duty cycle, actively pumping fuel into the filter regulator assembly at 91 PSI. As long as the return is not clogged or kinked, the flow back to the tank bleeds flow away from the assembly back to the tank, reducing the pressure and volume of fuel going to the front of the vehicle.

You give no indication whether you actually tested the return line as I suggested. I don't know what parts you're looking at, I don't know where you are looking at them, but most importantly I don't know why you're trying to replace something without seeing if it is defective. As I mentioned earlier, throwing parts at this is less than optimal and is expensive.

I used to be very tentative about working with fuel systems myself. If that is the issue, then take your time and you will learn that it is not all that bad after all.

Did you recheck the resistance of the ects per my recommended hints?

I haven't asked you to repair or replace anything yet, have I? I have not because changing multiple parts at once makes it much more difficult to track down the problem.

For example I don't know what the old etcs read in the car let alone at all because you put a new one in and measured that. Having a new one in doesn't tell you whether the old one was causing the problem. Or maybe I misread.

I'm doing my best to help you. It is your choice whether to follow up my troubleshooting recommendations or not.
​​​​​​
Firstly, as I mentioned earlier, get the fuel pressure red only at idle to ensure it is truly 91 PSI. If it is not, then I am barking up the wrong tree based on invalid diagnostic measurements. This is one of the reasons I am the last person to recommend you by replacement parts for something like this when the diagnostic measurement is made by some dude at AutoZone I supposed to a professional who understands how to use the gauge. It is not meant as an insult to you. What I want to avoid is you spending money on things you don't need and especially avoid you spending money on things you don't need because I said you needed them.

So please either follow the recommended troubleshooting steps or there is not much more I can do for you. I am happy to continue helping but if you do not agree with my recommendations that's up to you.

Ball's in your court.....

 

OK, please forgive my skepticism. It is based on my fault of not having patience with difficulties. Thanks for your patience with me and this problem, which is not your problem, except as you have adopted it in kindness to me.

I rechecked the resistance on the old ECTS on the bench, and it still appears to be open, with the multimeter set at 400 ohms.

I went back to the AutoZone that had a working usable diagnostic fuel pressure gage set and found this:

Key off, 0 PSI; Key on without cranking: 81 PSI, for maybe 3 seconds and then drops down to zero PSI quickly. Crank and idle 90 PSI and stays at that pressure, never dropping lower.

I'm getting ready to lift the rear of the car to see if I can tell what the pressure bleed off port is doing. I bought an AutoZone fuel filter in case you recommend that I install it.

I'm concerned about what the rich fuel mixture is doing to the Catalytic Converter.

I'll let you know what I find under the car.

 

ECTS can be up to several thousand Ohms when cold (ambient). set meter on 5 or 10KOhms setting as it can be more than 2KOhms.

Fuel Pressure.

Well, it builds up to 81 psi key on engine off -- which is in spec. the 3 seconds in the duration of the fuel system priming (-pump on 3 sec then shuts off).
Once primed, the system should bleed off next to nothing, maybe 5% of the pressure over 15 minutes. The fact that yours flies back to zero means there is a "leak" in the system.

It SEEMS there are 2 different problems going on Simultaneously:
There seem to be two obvious possibilities:
1) The fuel pump internal seal that prevents backflow is bad. Every time the pump runs, it's fine building the pressure but as soon as the pump stops, the seal/check valve /whatever that is supposed to maintain the pressure in the system doesn't. I THINK this would mean the fuel would flow from the line it was in (going to the front of the car) back through the filter/regulator, to the tank. The check valve would be part of the fuel pump assy itself. I do not know whether fuel backflow like this would find its way to the return line to the tank. My thought is no, as the pressure regulator is configured to redirect a set amount of flow and pressure coming FROM the pump. I doubt the fuel can physically go back through it and then out the return line to the tank. So you would not see it happening but you might hear it. So this would be a pump issue.

The problem with opening the line going up to the front of the car is that as soon as you do, all the pressure bleeds off instantaneously, you can no longer check for what you wanted to know, and there is of course fuel everywhere that came rushing out from the front of the car when you opened the line.

2) The fact that it is 90 psi at the port on the rail indicts the pressure regulator/filter assembly. It is simply not bleeding off the pressure/flow it needs to. The question is why. Is the return line to the tank clogged or is the regulator inside the filter regulator assembly wrecked.
Since a wrecked regulator could conceivably block the fuel path to the return port of the assembly and therefore block flow, you'd need to pull the piece of line and verify if it is clogged or not in order to differentiate the two situations. If that line is not clogged, then it is the regulator and a new assembly is required.

It should not be $200. DO NOT BUY PARTS YET

Return line from FUEL RAIL TO TANK: You definitely SHOULD see fuel from the rail return line to the tank with the engine running.