I just bought a 02 sc2 with 100K. The car is clean as a whistle and I have shined it up like a new penny. The car starts and runs well, no leaks, no smoke, no adverse engine noise. The only issue it has is a hesitation during light acceleration between 1500-2000 rpm. After that, engine picks up and accerates ormally.

I checked for the obvious. I changed spark plugs, wires. I cleaned throttle body and EGR passages. It looks like it has had a lot of new parts installed before I got the car. It has the upgraded ECTS and air temp sensors. New EGR valve. No codes, no engine noise.

I removed the valve cover to check the timing chain slack. It has about 9/16 in. deflection between the 2 camshaft sprockets. Is that excessive or not? I put a timing mark on the crankshaft pulley and checked the it with a timing light while running. With engine cold, the mark does not move much until it starts to warm up. Then, the timing mark starts to jump around from 5-10 (estimated) degrees at times. This does not seem right to me.

Does anyone have any ideas? thank you

02 SC2, manual trans, 100k

 

sounds like a possible ects related issue. REmove the ects connector and check for and clean any corrosion (usually green) on the connector or the sensor pins. If there is significant corrosion, replace the connector.

How do you know it has the upgraded ects and air sensors? Is this something you were told or have you actually pulled and verified this yourself (not questioning your integrity, just need to know which it is)?

Sounds to me like this car had a driveability issue and rather than sort it out, they just shotgunned all the common S car "trouble" parts to make it run better.

Probably has brand new coil packs and a DIS module to boot.

Back to the ects. Is there evidence that the connector has ever been replaced?


Can't seem to locate a spec on the timing chain allowable slack, but if it was terribly excessive, I'd think you might see weird wear patterns on the guides, uneven wear on the chain, wear on the inside of the timing chain cover, or more likely, you'd hear it slapping around when all is closed up and running.

If you are uncomfortable with it as is, you can always buy a replacement kit and have at it. Personally, I've never done one. Step by steps are outlined in manuals and posts online.

 

Check that frigging pigtail connector on the ECTS. I had one that had had the ECTS replaced, but not the pigtail. Upon close inspection, I discovered the squeeze connector on it was cracked and not making a good connection. I replaced that one and my starting and running miss went away.

 

jstreeservice:
Thanks so much for the quick reply. Im new at this, and might not know how to reply.

I checked the ects and aits connectors and checked for voltage. There was no corrosion or damage that I could tell. The sensors are the brass type and seem to respond when heated and cooled. I even switched them around and no change. I removed the coil packs and ign. module to check for corrosion. I cleaned all terminals and mounting surfaces. One coil pack looked newer then the other. I coated connections and mounting surfaces with silicone grease before assembly. I even removed the PCM and cleaned terminals and grounds. I silicone greased before reassembly.

I have no codes and I did the beer can trick to block off the EGR for testing purposes. No change.

I am not a professional tech, but have been working on cars and machines for most of my life. I have learned through experience that a lot of these problems are bad connections and can be fixed with little to no cost.

I suspect that someone through a lot of parts at this car trying to fix this problem. Whoever owned this car took very good care of it. It has minimal wear and body damage.

jstreeservice, 02 sc2

 

I will take another look at it. I switched the 2 sensors around for diag. purposes and no change. Other than this annoying driveability problem, the car runs nice.

 

If the ects connector does not seem to be the problem, measure the resistance across the ects (no wiring harness) with engine cold and at operating temp). NOTE THE OUTSIDE AIR TEMP for the cold measurement. Many of the aftermarket ECTS's have a temp vs resistance curve different than the stock OEM GM supplied part. Depending on what is in there, the coolant temp info derived by the PCM from the ects may or may not be accurate. IF it is inaccurate, it will cause the air/fuel mix to be skewed just enough to cause subtle issues like this. We always advise posters with hesitation/hard starting cold/hard starting hot/crank no start etc problems to verify spark, then change out the ects and connector with parts supplied by a GM dealer.

Oh, and the brass one can go bad, but the air temp one is unlikely to go bad as it sees very minor heat cycling comparatively. So if you swapped them you're probably good.

See if the part is a GM part before you run out and spend money on something you already have. I'm guessing it is because they finally started putting in the friggin redesigned brass ones the last year they sold the car...

Total cost (ECTS + connector (just do them both = $50 ish) if you go for it

If you choose to do so, please report back
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Alternative Thought

Front O2 sensor.

Why do I say this?

Because along with the ECTS, the front O2 sensor has the largest effect on air/fuel mix on these s cars. Coupled with your mileage (100K), you're getting near the end of life for yours. When they start to become significantly poisoned, their reaction times slow down, but not enough to throw a code. 1500 to 2000 rpm is probably the fastest accel range for the engine due to the way it is geared, so if the O2 can't keep up, the fuel mix feedback will lag and the air fuel mix will be off while you are trying to accelerate. (all this is real time theory in my head)

If you choose to replace, I recommend a Denso brand. No universal, no Bosch. My S cars hate front O2 Bosch sensors. You can get the denso replacement for the old GM part number for much less online than you can from a dealer or AutoBlown n the like--pls no one stocks it so it has to be special ordered anyway.

EDIT: Denso was the OEM supplied sensor, hence the recommendation

DENSO Part # 2341022 {#21022987, 21025117} OE Style Upstream Oxygen Sensor; DENSO is the O.E. Manufacturer $27.79 www.rockauto.com

Likely $50 at any brick n mortar store. Rockauto is your friend for saturn parts

 

Thanks derf,

I will check it out when I get back from vacation.

 

Finally figured out the driveability problem I was having. The no. 1 and 4 spark plug wires were switched around on the coil pack. This must have been done by the previous owner because i put them back where they were before when checking the coil resistance. The plug wires should be 1-2-3-4 on spark plugs and 4-1-2-3 on coils (standing in front looking at the engine).

I want to thank everyone for your help with this very annoying driveability problem. This car is a gem and want to keep it that way.

 

Glad to hear you got it straightened out. Happy motoring!