System too lean - TCCoA Forums

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post #1 of 18 (permalink) Old 02-08-2017, 10:08 AM Thread Starter
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System too lean

Have done reading and searching, I'm looking for insight on troubleshooting to see what exactly is wrong. I have the torque app & OBDII reader, I have electronic test equipment, scope, multimeter, etc.
I don't want to throw parts at it.
Details: fault code shows
current: P0171 Powertrain system too lean (Bank 1)
current: P0174 Powertrain system too lean (Bank 2)
I replaced all vac lines with the exception of: the EVAP next to the gas tank, looked to be in really good shape and the vac lines to the brake booster and into the cabin.
PO replaced: plugs, wires, coil packs, fuel filter, PCV & seafoamed engine. I can visually verify these were replaced, plus I have a box of the old parts that PO included.
The car doesn't really hesitate, but I think it should have a little more off the block. On occasion under aggressive acceleration it shifts incorrectly into 2nd. seems to shift, but no power for a couple seconds then goes, feathering throttle seems to help it react at that point. Sometimes in normal city driving the tranny seems to pop into 2nd then buck a little.
I've found these 2 write ups that seem pretty good general troubleshooting:
https://axleaddict.com/auto-repair/H...-Oxygen-Sensor
https://axleaddict.com/auto-repair/H...Airflow-Sensor
Car: 96 Cougar 4.6L Stock ~50K miles.
Any specific troubleshooting would be appreciated.
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post #2 of 18 (permalink) Old 02-08-2017, 10:19 AM
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MAF sensor involved in any way?
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post #3 of 18 (permalink) Old 02-08-2017, 10:38 AM Thread Starter
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Quote:
Originally Posted by Natesriv View Post
MAF sensor involved in any way?
Could be, just read through the write up on how to test that. I have cleaned it.

Another question: I've read that the intake manifolds cracking are common in certain years. I never had that issue with my 97. In searching I could not find details. Is my intake susceptible? How to test? I've read comments about propane, but how? Is it basically spray propane around the intake and if there is a leak the engine will suck it in and change revs?
Thanks.
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post #4 of 18 (permalink) Old 02-08-2017, 10:44 AM
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Quote:
Originally Posted by Kidd-7 View Post
Could be, just read through the write up on how to test that. I have cleaned it.

Another question: I've read that the intake manifolds cracking are common in certain years. I never had that issue with my 97. In searching I could not find details. Is my intake susceptible? How to test? I've read comments about propane, but how? Is it basically spray propane around the intake and if there is a leak the engine will suck it in and change revs?
Thanks.
The intake manifold cracks because it's basically a 20 year old plastic part, and due to heat cycling the plastic loses strength over time. They can last, they can go, it's kind of a crap shoot.

Generally speaking, the stock intake manifold will crack near the thermostat housing if it doesn't have the aluminum crossover, or near one of the spark plug wells where coolant is directed through it.
You'll see coolant in the spark plug well near where the crack is.

The propane test is that, if you spray an unlit propane torch around the intake, it'll suck it in.

I'm not well versed on the causes of the lean condition.

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2003 Explorer WAP block with Modular Head Shop "street ported" heads and Stage 2 PI NA cams, 75mm Accufab throttle body, C&L upper intake plenum, Kooks 1.75" primary/3" collector headers, 2.5" full exhaust with mid mount Magnaflow dual in/out muffler, 24lb/hr injectors, 80mm MAF, Tuning from Don @ www.lasotaracing.com, CAI that feeds from fenderwell. Jmod, 3.73:1 TL in Mark VIII carrier, Mark VIII aluminum LCAs, 93 Mark VIII driveshaft, PBR brakes (soon to be Cobras), 18x9 wheels with 35mm offset, 255/40/ZR18 Tires, Front and Rear strut/shock bracing, GR-2 shocks, Eibach 1.5" springs, 1989 SC front and rear sway bars.
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post #5 of 18 (permalink) Old 02-08-2017, 07:25 PM
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If you've never had the intake off, look at the #7 and #8 plugs, and see if there's any sign of coolant. that's a sign of an intake leak.

Grab the manifold and see if that side moves. No, really.

I had the alternator torque the intake to where the drivers side loosened up.

A propane torch, unlit, waved around the intake will show up bigtime on a live datalog of an idling engine.

Have a friend slowly go over everything spraying propane gas, and look for it moving back toward rich.

There's 5 short pieces of tubing in the evap circuit; the one everyone misses is in the passenger fenderwell, to the rear, between two hardlines.

Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
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post #6 of 18 (permalink) Old 02-08-2017, 07:58 PM Thread Starter
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Can EVAP cause this? I would think an EVAP leak would throw an EVAP code, it depends on how the ECU firmware performs the self checks and i guess a vac leak is a vac leak. I did get that hose. I'll look at that stuff, Grog6.
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post #7 of 18 (permalink) Old 02-10-2017, 03:39 PM Thread Starter
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I played around with Torque today attached is a screen shot. It appears from Torque that the MAF and O2s are working correctly. I'm going to set up the dataloging feature in Torque. I do remember now that the air temp was about 20 degrees higher than ambient, I saw a thermister near the MAF, that seems like a large temp increase. Can anyone confirm this is the air temp the ECU reports? I'll report back when I have a chance to get out and log.
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File Type: jpg screenshot.jpg (472.0 KB, 13 views)
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post #8 of 18 (permalink) Old 02-10-2017, 07:35 PM
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Quote:
Originally Posted by Kidd-7 View Post
I played around with Torque today attached is a screen shot. It appears from Torque that the MAF and O2s are working correctly. I'm going to set up the dataloging feature in Torque. I do remember now that the air temp was about 20 degrees higher than ambient, I saw a thermister near the MAF, that seems like a large temp increase. Can anyone confirm this is the air temp the ECU reports? I'll report back when I have a chance to get out and log.
If the car is sitting still, depending on location of the air temp sensor, the air temp can be warmer under the hood than outside due to the hood holding the heat in.

97 Thunderbird LX (The GT Bird)
2003 Explorer WAP block with Modular Head Shop "street ported" heads and Stage 2 PI NA cams, 75mm Accufab throttle body, C&L upper intake plenum, Kooks 1.75" primary/3" collector headers, 2.5" full exhaust with mid mount Magnaflow dual in/out muffler, 24lb/hr injectors, 80mm MAF, Tuning from Don @ www.lasotaracing.com, CAI that feeds from fenderwell. Jmod, 3.73:1 TL in Mark VIII carrier, Mark VIII aluminum LCAs, 93 Mark VIII driveshaft, PBR brakes (soon to be Cobras), 18x9 wheels with 35mm offset, 255/40/ZR18 Tires, Front and Rear strut/shock bracing, GR-2 shocks, Eibach 1.5" springs, 1989 SC front and rear sway bars.
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post #9 of 18 (permalink) Old 02-11-2017, 08:42 AM Thread Starter
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Quote:
Originally Posted by Woodman View Post
If the car is sitting still, depending on location of the air temp sensor, the air temp can be warmer under the hood than outside due to the hood holding the heat in.
I agree with that statement. In our cars though the thermister is in the airbox before MAF and after filter. The air is being pulled in from the outside, I found it odd to be a 20 degree delta. Admittedly, I don't remember details when I saw the temp. So yes, if the engine was warm already and had just looked at the temp when I first started then the thermister would have been warm from sitting in the hot engine bay and not enough cold air flow yet.
Kind of rambling, sorry, thinking this through.

I'm going to inspect the intake, propane test and datalog today.
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post #10 of 18 (permalink) Old 02-12-2017, 03:43 PM Thread Starter
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I smoke tested the vacuum lines today. Found some mild leaking around the TPS, I tried to remove it and add some RTV to seal it up. I can't break the screws loose and started to strip the heads out. Any advice on breaking the screws loose? Also, found some smoke seeping out around the EGR, looks to be coming out of the small holes under the disk. Is this normal? Or should that be sealed? I'm assuming its a diaphragm in there to restrict the flow, could that diaphragm be warn and leaking?
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post #11 of 18 (permalink) Old 04-06-2017, 08:57 AM Thread Starter
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I was reading an old post about the lean codes and have been going through my data logs to look for this cause. The air flow rate should be 0.7-1 #/min or 170-200 A/D counts; the Torque app shows this in CFM. Any ideas what the CFM flowrate at idle should be?
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post #12 of 18 (permalink) Old 04-06-2017, 09:52 AM Thread Starter
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Here's another MAF question. Attached is the graph of my data log from when I got on the highway till I parked. Is it normal for the MAF to vary that much while at a pretty constant speed and RPM? Max ~ 2482 & min ~ 78 CFM.
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post #13 of 18 (permalink) Old 05-06-2017, 10:51 AM Thread Starter
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Finally fixed this. From previous post MAF was the problem. I salvaged the MAF from my scraped cougar. I bench tested both and the resistance was very close to each other. Since I had the spare I put it in and reset the ECU. It's been weeks and no CEL, performance is better & more responsive. I data logged it and the fuel trim is near 0, while the MAF signals look much better. It seems at higher RPM the old MAF was registering much more airflow causing fuel to be dumped into the engine. The PO put a K&N filter in, so I my thought is the oil ruined the MAF. I can post a graph of the data log if anyone is interested.
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post #14 of 18 (permalink) Old 05-06-2017, 06:36 PM
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Congrats on fixing your lean condition. I see plenty of them here.

1992 Tbird LX 5.0, 3.73 gears, 1995 Cobra intake, deleted air silencer, 2.5" mandrel bent dual exhaust, SCP shorty headers. Updated four-hole fuel injectors. SK shift kit in AOD. Vogtland 0.9" springs, Tokico and Bilstein shocks.
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post #15 of 18 (permalink) Old 05-08-2017, 08:22 AM
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A better designed, oiless K&N filter is sold under the brand name AEM. Unfortunately, they don't make one for our car :-(.

They do make one for the larger intake used on the Marauder and '04 and up CVPI, but it is too large for the MN12 intake box.

Al

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post #16 of 18 (permalink) Old 05-08-2017, 03:55 PM
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Cutting away most of the bottom half of the airrbox just leaving the frame to clamp the factory filter in place did wonders for my airflow.

I understand there is a risk of vapor lock in puddles.

1992 Tbird LX 5.0, 3.73 gears, 1995 Cobra intake, deleted air silencer, 2.5" mandrel bent dual exhaust, SCP shorty headers. Updated four-hole fuel injectors. SK shift kit in AOD. Vogtland 0.9" springs, Tokico and Bilstein shocks.
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post #17 of 18 (permalink) Old 05-11-2017, 10:24 PM
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for reference, the maf voltage is what you want to log, it shouldn't vary any more than 0.03 volts during a stable condition

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post #18 of 18 (permalink) Old 05-27-2017, 01:38 PM Thread Starter
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for reference, the maf voltage is what you want to log, it shouldn't vary any more than 0.03 volts during a stable condition
I would prefer that, unfortunately Torque only records flowrate. I would much prefer to look at the raw data instead of the software's interpretation.
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