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Poor Fuel Economy


Danteval1
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From the shop manual on Reatta / Riviera

 

Poor Fuel Economy:

 

Definition: Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, economy is noticeably lower than it was on this car at one time, as perilously shown by an actual road test. 

 

Check:

- Engine thermostat for faulty part (always open) or for wrong heat range. See section "6B" 

- Fuel Pressure. See CHART A-5

 

Check owners driving habits:

- Is A/C "ON" full time (Defroster mode "On")?

- Are tires at correct P.S.I.

- Are excessively heavy loads being carried? 

- Suggest driver read "important facts on fuel economy" in owner's manual. 

 

Check:

- Vacuum hoses for splits, kinks, and proper connections as shown on Vehicle Emission Control Information label.

- Ignition wires for cracking, harness, and plugged.

- For proper calibration of speedometer.

- Spark plugs for cracks, wear, improper gap, burned electrodes or heavy deposits. Repair or replace as necessary. 

- Compression. See Section "6A" 

- TCC for proper operation. See CHART C-8

- For drafting brakes

- For exhaust system restriction. 

 

1989 White reatta with blue interior

I'm going to start to document my restoration and all the things I find useful in the shop manual. Please let me know if you need any. I also need a 1989 Reatta IPC if anyone has a good deal. I have two non working ones. 

 

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Are you experiencing poor fuel economy? What most of us have found to be #1 on a fuel economy list isn't even there; the O2 sensor. If the age and condition is unknown, it would be the first thing I would change. Monitor the O2 activity, fuel integrator and block learn in diagnostics.

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Just for reference, the early 90's Buick 3300, little brother of the 3800, usually found in the Buick Century granny Buick and others had no cam sensor or balance shaft. Performed well and delivered good mileage. 

 

A smaller 3.3 L 3300 was introduced in 1989 and produced through 1993. It is effectively a lower-deck version of the 3800, with a smaller 3.7 in (93.98 mm) bore and 3.16 in (80.26 mm) stroke for 3,344 cc (204.1 cu in). Like the 3800, it used a cast iron block and heads, push rods, and hydraulic lifters. Unlike the 3800, however, it used a batch-fire injection system rather than sequential injection, as evidenced by the lack of a cam position sensor. It also did not have a balance shaft. Power output was 160 hp (120 kW) at 5200 rpm and 185 lb·ft (251 N·m) at 2000 rpm with a 5500 rpm redline.

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Depends on how far you want to go. With a Moates.net ALDL setup you can monitor and record A Lot of things in real time on a laptop. Coolant, O2, long and short term fuel, knock sensor, timing, mpg, etc. Need real instrumentation to properly troubleshoot

 

gtpdash24may.jpg

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4 hours ago, Barney Eaton said:

The other one is the magnet on the cam sensor..........this will give both poor gas mileage and poor performance.

My reatta is throwing a code for cam sensor, still runs ok though.  Is it usually the sensor itself, or are there other things to check first?

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On 12/30/2019 at 10:40 PM, 2seater said:

Are you experiencing poor fuel economy? What most of us have found to be #1 on a fuel economy list isn't even there; the O2 sensor. If the age and condition is unknown, it would be the first thing I would change. Monitor the O2 activity, fuel integrator and block learn in diagnostics.

i just ordered one from amazon.13 dollars ac delco.

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On 1/1/2020 at 9:47 AM, padgett said:

The sensor is just a coil of wire. What usually fails is the magnet falls off the cam sprocket.

http://performanceresearch.us/padgett/cars/cammag.htm

 

Ah the plastic crumbs I found in the bottom of the oil pan when I did my oil pan gasket make sense now. I did not find the magnet though. I wonder if the magnet is stuck to the side of the timing cover or something.

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12 hours ago, 2seater said:

I assume MFA is the MAF sensor in the air intake? What engine temperature is indicated when not in closed loop?

 

Yes, MAF. My typical operating temperature is 190 F. I read that a loop closes at 170 F. I also cleaned the IAC and replaced the 02 sensor, let the carb cleaner burn off, drove it around the block. The MPG average was steady at 14.8. Ive also read that a new o2 sensor will be read immediately and so will the MPG changes. Ill give it a week to see how it does. Ive taken care of everything that I can think of as it relates to air flow. Next week, ill test the fuel pressure and injectors to see if theirs an issue. Barney has suggested that I change the cam sensor and magnet. 

 

As always, any suggestions on diagnostics, I will be grateful for. If I have any success with mpg improvement, I will post in the Reatta forum to assist other with similar issues. 

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3 minutes ago, Danteval1 said:

The MPG average was steady at 14.8.

 

Since you made several changes you will get feedback on the changes you made quicker if you delete the current average MPG from the trip computer and allow it to start over.  After you do that it will still take a while for the average MPG to level out so you get a good reading.

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I agree with Ronnie that a reset makes sense but I am most familiar with the non-touchscreen '90 which doesn't have as much functionality, so I defer to his knowledge. If it is indeed an average MPG reading it will take a large change to show up quickly, so starting over seems like the thing to do. Three things may help clarify what the ECM is seeing: look at live O2 cross counts to get an idea how active it is, more is better, look at the Fuel Integrator and the Block Learn live readings as well, best to do while on the move at various speeds and rpms. In a perfect world both fuel readings would be 128 but most systems aren't perfect and the readings should move around above and below that target at different rpms and engine loads. If they are stuck at 128 it is indeed open loop and more investigation is needed. It will give a good cross section of what's happening and keep the O2 good and hot. A good idea on the fuel pressure check but for zero dollars, pull the vacuum hose from the fuel pressure regulator and check for fuel leaking into the hose. It should be bone dry. Actually scrolling through the sensor readings is a good idea too, check TPS moves up and down with the throttle smoothly, idle at about .4volts, watch the MAF reading and see that it responds to changes to rpm and load changes as it should, more engine power = higher MAF reading, check ignition timing while moving, warm idle in park around 20* and a little higher when shifted into gear, and can rise over 50* coasting down.

 

One other thing I forgot: the torque converter will not lock up unless in closed loop either, which has a large effect on cruise mileage. What is rpm at highway speed? 2000 rpm in 4th gear and lockup is a bit over 70mph.

Edited by 2seater (see edit history)
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4 hours ago, 2seater said:

I agree with Ronnie that a reset makes sense but I am most familiar with the non-touchscreen '90 which doesn't have as much functionality, so I defer to his knowledge. If it is indeed an average MPG reading it will take a large change to show up quickly, so starting over seems like the thing to do. Three things may help clarify what the ECM is seeing: look at live O2 cross counts to get an idea how active it is, more is better, look at the Fuel Integrator and the Block Learn live readings as well, best to do while on the move at various speeds and rpms. In a perfect world both fuel readings would be 128 but most systems aren't perfect and the readings should move around above and below that target at different rpms and engine loads. If they are stuck at 128 it is indeed open loop and more investigation is needed. It will give a good cross section of what's happening and keep the O2 good and hot. A good idea on the fuel pressure check but for zero dollars, pull the vacuum hose from the fuel pressure regulator and check for fuel leaking into the hose. It should be bone dry. Actually scrolling through the sensor readings is a good idea too, check TPS moves up and down with the throttle smoothly, idle at about .4volts, watch the MAF reading and see that it responds to changes to rpm and load changes as it should, more engine power = higher MAF reading, check ignition timing while moving, warm idle in park around 20* and a little higher when shifted into gear, and can rise over 50* coasting down.

 

One other thing I forgot: the torque converter will not lock up unless in closed loop either, which has a large effect on cruise mileage. What is rpm at highway speed? 2000 rpm in 4th gear and lockup is a bit over 70mph.

 

I went into diagnostics when the car is cold, the loop was open. The loop stayed open until the engine reached around 165. However, this does not explain the poor gas mileage. I do not have a working IPC, so i do not know my speed. At highway speeds, I am around 2000 rpm and I can stay at a given RPM if I stay steady on the gas. 

 

Tomorrow, I will check the hoses, TPS, and MAF readings. I will also pull the spark plugs and test the cables. Something I haven't done. I'm starting to think that I have a faulty MPG reading. I drive around town and $10 will last me a while. Though I dont have a gas gauge, I can hear the pump begin to struggle when my gas gets low. Jim Finn sent me a new IPC and it should be here Monday, i'm crossing my fingers for tomorrow though. Ill keep updating as I go. I enjoy this whole process of problem solving. 

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I see, the mileage issue may, or may not exist at all?? From the first comment, it sounds like it does go to closed loop and you have no way to measure speed and distance. You really need that to calculate the actual mileage, and a gps unit can do that for you or even on your phone but it would need to accumulate the mileage.

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14 hours ago, 2seater said:

I see, the mileage issue may, or may not exist at all?? From the first comment, it sounds like it does go to closed loop and you have no way to measure speed and distance. You really need that to calculate the actual mileage, and a gps unit can do that for you or even on your phone but it would need to accumulate the mileage.

 

I'm learning about the car as I go. What may seem like common sense may take me a minuet when it related to this Reatta. I found out the car does go into a closed loop after further reading. I posted something new regarding the issue. Thank you for your active engagement. It has really helped my issue. If you coul comment about this next one, it would be helpful. It relates to the MPG but the ignition aspect of it. 

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hello,

 

I feel like I should mention this too, I passed California smog with flying colors. No issues at all. This was in November and i've been doing a lot of reading on the car since then. I think its giving me a false reading. Driving on the freeway, my RPM is 2075 at 75 MPH with the torque converter engaging. I'm still trying to fix many things on the car. My attention has shifted to fixing my Teves brake system. If anyone wants to comment on that, it would be a great help. 

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1 hour ago, Danteval1 said:

My attention has shifted to fixing my Teves brake system. If anyone wants to comment on that, it would be a great help. 

If you have a specific question maybe someone could help you out.  Don't know what comment to make without knowing the problem you are having.  If you have mentioned your brake problems before please refresh our memory.

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