2001 Saturn Sc1. I have read over the threads here trying to figure this out. I am still getting the dreaded PO340 code. I could not find any with a solution.
It seems anytime you change the coils, plugs, wires, control module that the coils set on, this code is going to show up.
Drove fine one day and the next day it would crank and not start. Changed crank sensor, no start. No spark but getting gas. Bought new wires, NGK 7755 BKR4ESA-11 standard copper plugs, and coils. Would not start. Bought a new ignition module that the coils set on. Wire wheeled the bolts to clean them up and used dielectric grease on the module and plug wire boots, everywhere. Cleaned the mounting area where this all mounts to with wire wheel on a Dremel tool. Was pleased when it started, but now the PO340 code comes on, Dang it! I changed the intake gasket years ago because of the common problem but I sprayed starting fluid around it to see if it was the problem again. No change in the engine running. It had some egr and intake codes that I have dealt with in the past, another common problem with these cars, that I took care of again. Cleaned all that out so should be good. Cleaned the exhaust ports out a few years ago. EVAP codes also that has been on for years since I had the car. Tried unsuccessfully fixing that so I gave up on it and just drove it. No other codes than that. Car has almost 170,000 on it. I think it had under 100,000 when I bought it. Checked all fuses and grounds and they are good. I understand the cam sensor is getting it's signal from the ignition module from one spark wire, simulated. Before I take it somewhere to let someone else figure it out, is there anything else I can do? What happens if I drive this car with this code on? I have a code reader that does some live readings, but I have not the knowledge to understand what I'm looking for. Thanks Russ.

 

1) There no physical cam sensor on the s series engines. But the waste spark ignition system detects what it needs.

2) please pull all 4 plugs and

• Shine a light down into each spark plug well. They should all be dry. Let us know if there's any oil in any of them.
• Measure the gap on each (and report)
• Upload a pic of the four plugs
• Since you have them out, do a compression test to check overall general health of the engine.

3) what evap codes sre present?
4) how much oil does it burn per1000mi?

5) If you have performed any repairs with the battery disconnected, I believe you should have had to go through the passlock we learn procedure. However, I see no mention of it in the description of your repairs, which is quite detailed.

P0340 on an s car essentially means the PCM is not happy with the ignition setup as configured. That is a broad statement and as you have already encountered, it can appear for many different reasons.
I would also recommend you do a coil resistance test on both coil packs, and at night, pull all of the plug wires off of the coil towers. Pull the fuel injector fuse, and have a friend crank the engine for 5 seconds at a time while you watch the coil towers. You should see an arc between the posts on one tower, then the other, then the first, etc reattach the plug wires to the coil towers, making sure the plugs are connected as shown on the sticker across the front cross member.

Perform a basic spark test with each plug to ensure you have a nice spark and that they are reasonably equal across the plugs.

Plug the fuel injector fuse back in and reinstall the plugs.

Yes a lot of this sounds very basic, but it doesn't take much to throw a p0340.

 

OK. Pulled the new sparkplugs and checked gap. It is .040 as it should be. Looked with a light in the spark plugs wells. Had gunk in there but not super oily. Used a shop Vac with a small hose and scraped around with a pointed awe and sucked up stuff. Compression test is,1st cylinder 135, 2nd cylinder 125, 3rd cylinder 125, 4th cylinder 118.
Measured the new coils at 11.10 k ohms and 11.35 k ohms. I measured the old coils at 7 something K ohms on both and decided to put them back on and try them. Well it started with the old ones leading to the original faulty ignition module which was the cause of the car not starting. But I still have the PO340 code. Pulled fuel pump breaker and I watched all the coils spark across each other with the wires off while cranking. Old and New coils. While it was running, I pulled each wire off one at a time and each one was sparking good. The engine would studder a bit and I could hear it sparking. I have worked on the car over the years disconnecting the battery and have never had to do a pass lock relearn procedure. The car has always had EVAP codes that I could not solve but I just drove it like that for years. About once a year I would have to clean the EGR valve and intake for the codes it would give for that. Put quite a few EGR valves on it until I figured out they just need cleaning, and cleaning ports that I use a Bass guitar string to do. It works and the codes wont come back for awhile. It was time for the wires and plugs that's for sure. When I purchased the ignition module from rock auto, I bought the cheapest one on there. $30 maybe. Could this be the reason for this PO340 code? The ACDELCO is $114 and I would buy it if that would solve the problem. I top off oil in between oil changes probably less then 2 quarts. Have always changed oil when the light came on. This car has an oil leak around the front of the motor. Using sealer in the oil has slowed it allot. The car does not smoke when starting or driving. The new plugs have only been run an hour so not much to see. Thanks for the help Derf. Russ


Old Plugs

New Plus

Old Plugs

 

Did you do the compression test with the throttle held wide open and the engine at operating temperature before turning it off to do the test? If not, those numbers are not of value.

check the wiring harness to the ICM very carefully.
If you have put anything like dielectric grease between the coils and the ICM, remove it. Also make sure you are getting good contact between the underside of the head of the bolts for the ICM and coils with the visible metal surface below it. I don't think it should matter, but if there's any dielectric grease between the bottom of the ICM and the bell housing, wipe that off as well.

Those bolts provide a ground for the ignition system. If that is not solid, you will likely have strangeness.

I see that you stated you used dielectric grease everywhere.
Remember that dielectric grease does not conduct electricity. It is used to protect electrical connections in an automotive application. So for example, If two components that are connecting do not connect tightly enough, you can actually end up with a thin layer of dielectric grease between the conducting surfaces of the two components.

The ICM module uses capacitive plates located underneath the 1/4 coil to determine the polarity and voltage amplitude of the secondary (waste spark) firing of 1 and 4 through the 1/4 coil.
So I don't think you want anything in that gap between the bottom of the coil and the ICM module

 

Derf, Took everything apart and cleaned all the dielectric grease from the ignition module. I did have some around underneath there. Reassembled it and checked that things were flat and grounded. Started and still have the PO340. I checked the wiring from the connector to the computer by the battery. Took connector to the computer off and did continuity between the two connectors. All good. Started car and got it to operating temp. Turned it off and pulled the fuel pump fuse. Pulled all the plugs and did compression check again. Had the wife old the pedal to the floor and crank it for each cylinder. Cranked till it did not go up anymore. #1 was 130, #2 was 165,
#3 was 165, #4 170. #1 not looking so good. I put a screw in rubber hose on that #1 and its stuck. Dang it. Finished the rest with rubber push on stopper. Hoping I can get that out of there when it cools down? I cleaned the ground off at the computer and added a thick copper wire there to ground. Did not make any difference, still have this code. When I get that compression hose out of there with spark plugs back in, I guess I'll have to take it somewhere. Can I drive it awhile with that code on so I can take it somewhere? Thanks Sir, Russ

 

P0340 Diag tree and wiring diagram
From Charm.li . Includes diag tree, conditions under which code is triggered/what the PCM is not seeing what it expects to see

 

I wonder if the lower compression is triggering this code? That is a great diagnostic aid on the charm.li page, it explains how the logic determines when #4 fires. I am sure the early L61 uses similar logic since the cam sensor is inferred.

 

Clean off the coil towers. I use very fine sandpaper but a scotch brite pad will work

Have you checked the resistance of your plug wires?
If there is any corrosion at the clips on the ends, replace the wires with ones that meet the resistance spec of 1.5 to 15 k ohms. Also check for arcing on the one and four wires.

Make sure the bolts that hold the coils to the ICM are making good electrical connection to ensure a solid ground. This is in addition to the bolts that hold the ICM to the bellhousing.

The voltage required to fire a cylinder with good compression is higher than the voltage required to fire a cylinder with not so good compression.

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The ignition module may be detecting the difference in voltage level required to fire number one compression versus the voltage level required to fire number four on compression. If the voltage required is significantly different, then this may be the source of the code. Which ultimately condemns cylinder 1.

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It is possible that the ICM/EI module purchased is either defective or the PCM doesn't like what's coming out of it as far as the monitoring goes.

I am not one to spend other people's money.
Try putting your last ICM module back on and see if anything changes.

 

Another cross post with Andy (timewise).
I love those, because I get to see if what I've come up with actually makes sense.

I had to finish mostly understanding the finer points of a waste spark system to come up with what I did above. I'm glad it's reasonably aligned.

 

For the record, I'm surprised you don't get a constant misfire at 130 PSI. The service limit is somewhere around 180.