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Old 05-18-2018, 07:06 PM   #1
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I am experiencing significant gas mileage loss and some weird symptoms that I do not understand. After consulting a mechanic he suggested the turbo was the issue and to see if I was getting white smoke upon start up. Here's some background to the car.
I always had poor gas mileage from the moment I bought my `03 SAAB 9-5 Aero. It had 120,000 miles.
The prievious owner had substantial proof that he had taken great care of the car oil changes, inspections, minor service. No issues no codes. Clean car fair deal. Being a bit of a noob I thought poor gas mileage old car no big deal.
To remedy the gas milege I began doing a full inspection myself. Dropped the pan clean enough. Looked inside cool. I changed the plugs with the correct NGKs torqued em lubed em up with some dialitic grease-beuno. Immediate improvement. And with an oil change every 2500 miles the car ran great. Gas mileage was a solid 20, not bad still low. And then as it got hot for summer became ever lower down to 16.
Down the road maybe a month or two I got a code for sooty plugs (P1312 I believe) pulled em out sure enough they were grimey. Dang, changed them again, back to 20. A week later dirty plug code comes on again. Then goes away within the day. I decide to change all the vacuum lines. No real improvment. The next day I pop open the hood after work a bit of white smoke was coming from behind the engine eminating from the area behind the ignition and in front of the oil cap. No real tangible location I could see. There wasn't mucj of it. Didn't have a particular smell I could identify. Shoot, I think "we'll I'm doing some work changing the timing belt engine mounts soon I'll get to it." The next day the whote smoke is much worse, but still not a crazy amount but suddenly the gas mileage is PLUMMETING 11, 10, 9... even as it idles. No significant smoke from the exaust. Theres a strange smell in the cabin not antifreeze or oil just weird. Oil looks normal.... What is happening to my baby? What more info can I provide?

Last edited by Sanctum; 05-18-2018 at 07:17 PM.
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Old 05-19-2018, 04:03 AM   #2
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How old is your DI cassette (ignition coil). Low 20s is not unusual for these cars depending on your driving habits.

There is no such code as a "dirty plug" code. 1312 is a misfire code, meaning something is causing the car to misfire. Could be fuel, air, but mostly is spark related. Primarily this is a code suggesting a problem with your ignition cassette. Bad plugs could cause it too but you have to rule out the ignition cassette.

I think you have two options. 1) buy a new genuine DI cassette. They are about $300. 2) Try your luck with a used one (not a great option but I'm not sure of your budget)

There are off brand cassettes for less money, do not buy one.
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Old 05-19-2018, 07:47 AM   #3
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Ah yes. I considered that. Luckily, I have a trusted autoshop that will allow me to install most anything. They have one in stock fairly cheap. You're definately right I should do what the code says first haha. It's the smoke that had me worried. Will update with its status soon.
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Old 05-19-2018, 02:18 PM   #4
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Unfortunately, after putting in a brand new cassette no change in behavior. The MPG continues to lower. No engine lights. No smells. No noises. Did not run the car long enough for smoke because the MPG continues to drop lower each time.
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Old 05-19-2018, 06:05 PM   #5
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Are you sure you don't have a fuel leak that just hasn't caught fire yet? The injectors are on the back of the engine right were you're seeing "smoke" and the catalytic converter is directly below.

I've actually had an o-ring that didn't seat correctly and had raw gas back there, the gas was vaporizing when it hit the cat but no fire thankfully.
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First T7 19T turbo setup. First T7 Deka 80lb. injector setup.
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Old 05-19-2018, 06:10 PM   #6
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Other than that, I'd think about changing or swapping in a known good 1st oxygen sensor and after that a mass air flow sensor. Coordinated failures generally aren't very likely form a probability standpoint, but I suppose it's possible that both the MAF and the 02 sensor have failed or become lazy in a way that's coordinated so you don't see a code.

These things do need good ignition cassettes and plugs, it sounds like you have that covered. You're absolutely sure there's not an air leak anywhere?
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First T7 19T turbo setup. First T7 Deka 80lb. injector setup.

Last edited by Trionic3000; 05-19-2018 at 06:13 PM.
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Old 05-19-2018, 09:00 PM   #7
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Thank you for the fast responses and patient answers. I did clean the MAF first thing, that and the plugs are what got me up to 20 mph. Someone else recommended an O2 sensor. I will do both tomorrow with multiple O2 sensors to make sure I have a good one.

Im not positive theres no leak. Im just not sure how to go about finding out for sure so I did what I knew first. Like replacing the rotten vaccuum lines. A fuel leak sound's scary. You're suggesting I should pressure test the fuel system? I will have research how to check for leaks. I have not performed any of those tests. Any particular best test I should use? I have access to many tools for testing.
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Old 05-20-2018, 05:26 AM   #8
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I just thought of something that's more likely: coolant temp sensor and thermostat. They're cheap. One of the failure modes for the coolant temp sensor is to read artificially low temperatures, when that happens you won't get a code, and the engine management continuously runs in enriched warm-up mode. That'll give you bad gas mileage without other symptoms (except that it won't run the radiator fan unless the AC is on, you won't actually see an overheat if you use the AC all the time). And if the thermostat gets stuck open, that'll also cause too low coolant temperatures and running in warm up mode.

As far as testing for a fuel leak, I'd just turn the car on and lift the plastic cover and do a visual inspection for wetness while it's running. You could have a leak AND something else wrong too--seeing white 'smoke' isn't explained by a bad temp sensor and/or thermostat. Maybe you have a coolant leak back there? The throttle body is in the coolant circuit so that it doesn't ice up when it's cold out. Coolant dripping onto the cat makes a sort of sweet smell. Maybe that's the smoke?

If the car's running in warm up mode all the time, it'll eventually foul the plugs too, and when you replace them that might appear to 'fix' the underlying problem.

Number one I'd try replacing the coolant temp sensor and thermostat (and plugs if they're wrecked again) before doing anything else. While you're back there at the temp sensor, make sure to inspect/clean-up the grounds to the intake manifold and block(?) too, I think there are two there under 10mm bolts if I'm remembering correctly.

Also, I don't know about cleaning MAF's. I'd replace it with a new genuine unit, at least to test.
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First T7 19T turbo setup. First T7 Deka 80lb. injector setup.

Last edited by Trionic3000; 05-20-2018 at 05:36 AM.
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Old 05-20-2018, 11:15 AM   #9
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Well just got done changing the temp sensor and the thermostat. What I did is u drained the coolant, unplugged the air intake, took out the battery, replaced the thermostat then replaced the coolant temp sensor. Filled up some coolant. When I went to start the car the engine light began flashing, the turbo gauge going back and forth, and the gear indicator flashing between park and low. Will crank. Won't start.
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Old 05-20-2018, 11:17 AM   #10
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The recent odometer, not the overall miles has also been reset, the date has been reset... did I short something?
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Old 05-20-2018, 06:49 PM   #11
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Did you figure it out? Something you did while changing the temp sensor and thermostat is causing it. Are the battery terminals tight, is the intake pipe loose or something? The trip odometer will reset when the battery is removed, that's normal. Good luck
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First T7 19T turbo setup. First T7 Deka 80lb. injector setup.
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Old 05-21-2018, 09:47 AM   #12
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So far it's been raining have not had a chance to get back into it. I did do a brief glance over nothing obvious was wrong everything was connected. I am worried that when I went to take out the battery my ratchet slid and grounded the positive and let off a serious spark. I did check over all of my fuses after and there was nothing blown. Not sure that matters, maybe im dumb and that's why, although I'm unsure what it did. I will be doing a more thorough check and update as soon as the weather permits. For now here's a brief summary of the steps I took:
I removed the plastic air intake tube completely.
I removed the battery completely.
I removed the hose connecting to the thermostat housing & radiator completely catching any drips left over on some paper towels.
I removed the housings 4 screws. I noticed something that was something grounded to the housing via one of the screws.
I removed the thermostat replaced it, put the housing on.
Then I disconnected the temp. sensor, unscrewed it, replaced the new one, reconnected it.
Reconnected the hose.
Reconnected the air intake, reconnected the wires to the air intake.
Reconnected the battery.
Seemed pretty clear cut. Will check everything soon.
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Old 05-21-2018, 10:49 AM   #13
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double check the air tube is seated on the throttle body soundly. It's easy to get that crooked or off slightly.

It sounds like you checked the ground wire too that has to come off when you do the thermostat.

Those are the only two things I can think of that would affect starting. It's possible you pulled one of the vacuum lines off while working there but less likely and I'm not sure if that would be enough to keep the car from starting.
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Old 05-29-2018, 09:38 AM   #14
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Got out there to check on things finally. After looking closely at the ground I realized I had used the screw to hold the thermostat housing down (with the washer) as the ground screw. After switching the two car quit freakin' out and started right up. I pumped out the air bubales and took it for a ride around the block. The MPG are now at 16 so it seems that the temperature sensor and thermostat are exactly what it needed.
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Old 05-29-2018, 09:39 AM   #15
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Thank you everyone!
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Old 05-30-2018, 09:14 AM   #16
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nice, glad you got it fixed
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