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Hello,
I’ve got a 2’01 Catera that I’m trying to troubleshoot. Only 2 codes, P0171 and P0174. CHECK ENGINE has been on for 2 mos. now. When starting, it starts just fine without issues. When put into reverse that initial loading onto the motor makes it almost sputter, then it evens out and the car is totally fine, both city and highway.
I made a makeshift smoke machine, propped open the throttle body with some soft vinyl tubing, and pumped smoke in from the intake all the way through the plenum. It was one pass with the smoke machine for a good 7-8 minutes and I did not see any leaks in the front part of the engine bay.
With car on and PIDs on display pressing the accelerator causes MAF value to change on the scanner. Inspection of MAF sensor with eyeballs looks clean and shiny.
— Freeze frame for P0171
engine 2260rpm
calc load 22.7%
coolant 187degF
LT FTRM1 22.7
ST FTRM1 -0.8%
LT FTRM2 21.9%
ST FTRM2 0.0%
VEH SPEED 60MPH
FUEL SYS1 CLSD
FUEL SYS2 CLSDend of freeze frame —
Cadillac Forum http://bit.ly/1dmCcRY says that it could be a bad MAF sensor. But mine is still giving values. Maybe they’re bad values?
There was also a Catera post someplace about there being a vacuum leak near the brake booster. Videos by ETCG and ScannerDanner show how to check this, but on this car I don’t know where that is.
Vapor recovery is not working right when I fill up on gas. But it’s been like that a long time before the MIL showed up.
What to try?
Thanks
This issue is fixed. Thanks for everyone’s help! :woohoo:
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Ugh. That one is a problem child. Why the powers that be at GM decided to put a damn Saab engine into an American car is beyond me. The fact that it can change values on the MAF pid simply indicates it can read, but very well may be reading wrong. Is your air filter stock or aftermarket with oil on it? Have you tried spraying MAF cleaner on the sensor? If you do so you must let it get completely dry before you plug it back in and turn the key on. Since you’ve seen the Danner vid you know that the only certain way to get a good read on the MAF is a scope. You said you rigged up a smoke machine into the intake, but did you check the intake ducting real good with a bright light?
Usually this is going to be either a bad MAF or unmetered air getting in after the MAF. There could be a ducting issue where the hoses come up, and they are just plastic. Might want to spray a little carb cleaner around while listening to it and have someone watch the short term trims. They will go up and down normally, but if you hear a pitch change in the motor or the short term trims suddenly dive deep negative you found your leak. Under the throttle body is a breather hose, so don’t forget to look at it.
On the grid picture showing the brake fluid reservoir, location I-5 is where the brake booster hose goes into the check valve. If the booster itself leaks vacuum you might not see it under the hood with a smoke test, and the check valve would prevent you from getting smoke in there anyway.
Thanks for the info you have posted. The freeze frame data helps, and laying the grid out on those pics really helps us get on the same page with you to give you better information. If I was making a thread about how to post in order to get help, I would show your post as an example.
– MAF sensor looks clean but not sprayed yet.
– Air filter looks like an orange FRAM. Dry, no visible clogging.
– When smoking, areas around the motor patrolled with 2-tube work
| light; 1-2 minutes per spot. When duct was pulled from throttle
| body afterwards, smoke was in the hose. Worth noting that no
| particular attention was paid to the breather b/c I didn’t know
| about it.
– Before smoking, I was looking for vacuum access around the upper
| manifold. I undid the booster hose fitting on the manifold
| side, and dismissed it as a vacuum hose because gasoline came
| out.I drove the car today. It seems noticeably worse by a small notch. Hoping that it will help shoot the problem easier.
Got my hands on a can of B-12. With engine cold, started it up and began spraying from the driver side to under the upper manifold, from the passenger side to under the upper manifold, front of throttle body, left side of throttle body, right side of throttle body, under throttle body onto the breather hose clamp, brake booster hose manifold-side fitting, brake booster hose booster side, above the 2 cylinders near the timing cover on both sides, straight past behind the upper manifold, and onto what looks like the variable control vacuum solenoid. No big swings in RPMs were noticed.
The Danner video I saw was one where he squeeze-tested the booster hose and it showed a gross amount of leakage. Because of your comments, I found his video for MAF sensor output testing on a Buick.
Once I figure out access to the MAF connector I can easily scope it. But I don’t know where to get the datasheet with the normal output characteristics.
Thanks for all the help. Makes the process much more stable. Yes, damn Saab motor.
[quote=”MILhouse” post=135285]- – Before smoking, I was looking for vacuum access around the upper
| manifold. I undid the booster hose fitting on the manifold
| side, and dismissed it as a vacuum hose because gasoline came
| out.
.[/quote]You had liquid gas sitting in a vacuum line? That’s not supposed to be like that.
The MAF may look clean but it only takes a thin film of crud to coat on the wires and screw with a signal. As far as a known good scope form, I think Danner had a vid showing a GM one. If I recall off the top of my head this is a frequency generator type and will increase the hertz the higher it reads. I do know a friend with an L-series Saturn the same year as your car and with that same damn engine. I’m not sure how soon I could get over to his place but I could snap a shot of a waveform on his with my Modis and try to post it for you or PM it or something. Another thing I like with my scope is that if I pick what I’m working on it will set my scales automatically for me and has a database with known good waveforms already in it. What kind of scope are you using?
Is your makeshift smoke machine capable of making any pressure? I can’t see the device so just trying to keep things straight in my head of exactly how this was tested. You mentioned when spraying the carb cleaner that “no big swings in RPM” were happening. That’s not what you would usually get when you find a leak though. Were you finding subtle changes in the pitch of the motor? If it has a quick enough response on the IAC you might hear very little. I actually had a 1/2 ton GMC truck with a vac leak once and I watched my fuel trims and O2 readings while I sprayed it. I found the leak but the motor didn’t make any noise telling me I was onto something. Just saw the STFT diving and the O2 hit near .9v when it shouldn’t have.
Yes, clear liquid fuel dripped out of the vacuum hose.
Auto Parts Warehouse says the Delphi equivalent for the MAF sensor is DELAF10160.
OK, I will clean the MAF along with continuing testing. I’d like to make sure that if the MIL can go away that it stays away for a long time.
I’ve got an older Tektronix handheld. Not purpose-built for this problem, but with the right information verification may be done. The Modis has a sensor waveform database? That’s really, really nice. I’m not comfortable with you going out of your way to scope the Saturn. If the Modis can specify expected parts of signaling that already sounds beneficial.
For probing the MAF, I need to introduce some wire shunts that I can clip onto, or get some alligators. The harness end has a soft rubber boot and I’m not confident I can pull it back without damaging it.
So I got an extension cable for the scanner. I set the Actron to watch the PIDs and repeated with the carb cleaner. The RPMs did not noticeably change on the belt as far as I could see, and like last time, the pitch variation was about the same. I’m not sure if the scanner is good at looking at live fuel trims. It reported changing values for RPMs and the MAF in real time just fine, but LT FTRM1/2 was 24.5 and ST FTRM1/2 was 0.0 and these 4 FT numbers just sat still there like rocks. I revved and blipped and they just sat there.
I think you’re right about the smoke machine. I’ll take a look at it and do another pass.
The earliest I’ll be able to touch this car again is Friday evening I think. Other than that feedback at your leisure is welcome.
If you go to a sewing supply section of a store get some t-pins. They get into the backside of wiring plugs quite nicely. You see them used a lot in ScannerDanner vids. Getting rid of the engine light is going to be the challenge of the day it seems, but with your fuel trims running +25 or so obviously there is an issue.
Trying to think a little and not focus too narrowly on the problem. Getting tunnel vision can send a guy chasing his tail a bit. That vac hose has me thinking though. Can you look for misfire counters? If you get a miss, your engine commands more fuel as the extra O2 is seen as a lean condition. With fuel in a vac line I would wonder if your fuel pressure regulator has a leak on the diaphragm which allows enough fuel in to choke it off a bit. The misfire it causes when doing that sends extra o2 past the o2 sensor and the ECM thinks you ran lean.
While with most anything GM I go for Delphi/ Delco parts, remember that Bosch was the OE for most everything on this motor as it is Saab. On that Saturn I worked on I actually had good luck getting parts at Advance Auto because they are basically Bosch’s whore. But for something where I needed an exact OE part, they had it in stock. I don’t particularly like Bosch products unless it was something that took it OE.
Your scope can be used quite well for what you are trying to do, you just have to know where to set your scales at and read the waveform right. The database on the Modis does certainly shorten the learning curve but its not cheap. About a grand a year to update it. Right now I can get up to 2012 models American and Asian. Never got the euro software as I just hate working with euro cars.
By the way, those torx headed bolts all over your motor are not regular torx. They are torx plus. A regular torx socket won’t get all the way down and feels sloppy because torx plus makes a slight bell shape at the bottom. Had to buy a set of sockets for it from my snap on rep when I got dragged into dealing with that Saturn motor.
Its not a big deal for me to go scope that Saturn to help you out. The car is only a few miles from me and is owned by a friend. What could be of some benefit for you is to scope the signal before and after you clean it. Then you know if you have made any sort of change to the reading of it.
Have you seen this vid? Seems like it might be useful.
Going from the freeze frame data, it seems your lean codes was under a load condition, so I wouldn’t be looking for a vacuum leak. Check fuel trims at idle, see if they are low at idle and increase as you increase rpm.If so then its probably a fuel delivery problem or dirty mass air flow. Have someone drive the car warmed up and check your oxygen sensors( bank 1 sensor 1 and bank 2 sensor 1) at wide open throttle(be careful and watch the tach for redline) the O2’s should go rich reading about 800 mv, if it shows lean, then its either fuel delivery or dirty mass airflow that is likely. Check grams/sec at wide open throttle and look for around 150 grams/sec if so then check fuel pressure, if not then clean mass air flow.
The scanner reads 99 PIDs but only displays a fraction of them. Dipslayed ones are:
MIL statys
throttle
RPM
calc load
MAF lb/m
coolant temp
IAT
IGN ADV
secondary air
fuel trims
o2 sensors 12 and 22
fuel sys 1 and 2Sorry, no misfire counter.
So I got the boot off of the wiring harness. It turns out that where each wire meets the pin inside, it’s covered in plastic sleeve. It won’t push through either. Why do that? There was already a boot over it. Overdone.
Thanks for the heads up about the torx. I don’t have torx plus. I also don’t have external torx. I also don’t have security torx. Ordered a master torx set by OTC and it should be here Wedensday. Having to get more drivers is sort of OK, but not great.
I think I want to change out the fuel regulator. It has a bad symptom already, and it seems to be the only definite one so far. Do I need to get new intake rings? I’ll also get some scanner telemettry with some driving, and smoke the vaccum again.
I don’t mind adding to my toolset when I know I’ll get a lot of use out of them, but I hate buying tools for a car I don’t plan to deal with ever again.
If you are taking off an intake plenum you will need to replace the gasket.
Fuel pressure regulator —
Removed the upper. Tested the fuel pressure. Changed the FPR.
Went for a drive the next day. Fuel trims not improved, but at least the regulator is out of the way.
MAF sensor —
Finally able to tap the sensor. Um, because it’s a Bosch part, f 00c 262 930, it turns out it’s a DC signal. I myself was expecting a square wave.
Funtionally the output looks OK. I don’t have spec values to verify it with, but it reacts as anybody would expect. There is also a noisy pulse that happens now and then, but it’s pretty short. I doubt the ECU internally notices this.
After testing I hosed the sensor contacts with MAF cleaner like crazy. Let it dry thorougly. Drove the car. Fuel trims not better.
O2 values —
Took a look at the codes again. Some junk codes were in there from the car sputtering after changing the FPR and getting air in the fuel rail. Erased the codes. The trims got zeroed out.
Drove around. The sensors put out lots of values, and as far as I could tell without running over neighbors walking their dogs, the values were between 0.15-0.67 volts. And the 0.15 was nearing a stop sign. If that is right, then there is a leak hiding somewhere that I haven’t found. Also, it took around 5 minutes for LTFTs to get up to 18.
I’m going to diddle around with smoke testing and vacuum hoses.
Found small leaks in the intake hoses.
Oil filler cap o-ring was leaky.
Spark plugs fouled. Crud on the pistons.Crankcase ventilation seems good. EGR valve seems good. Didn’t check the IAC.
After fixing the above, the car still wasn’t running better. Pressure tested the intake and plenum 3 more times and there were no leaks anymore.
Scoped the MAF voltage again, and it looked the same as before with the same responsiveness. Idle was still around 1.1 volts. I have the Chilton service manual, and it doesn’t say what it should be normally; it just gives the values that trip the ECU.
Engine ran better at idle with MAF unplugged. Figured that the MAF was the last thing. Took a chance and replaced it with a Delphi resold MAF (Bosch).
Car immediately started running better. Test drove it for 30 miles and got 3.9/3.1 for LTFTs. So on this car the MAF sensor can be skewed badly with no MIL but it has to be shot to make the ECU throw a code. :woohoo:
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