? MAF Sensor Problem - 95 Olds Regency Elite w/Supercharge Engine


#1

Coming up with these codes:
P0172 (x2) - Bank 1 system too Rich (two injectors failing on front bank), P1257 - Boost control fault system overboost.

We replaced the two injectors but the system is still running too rich. Question: What is causing injectors to run too rich still?

Additional information: Already had car in a local top tier shop they replaced the MAF and the O2 sensor, the TPS was also replaced. The car runs worse now than before, the gas peddle feels like mush now, before it was firm and very responsive with the old MAF sensor. The car idles better but has no pickup and falls on its face as soon as the speedo hits 50 MPH. If you try to speed up the engine while in park as soon as the tach hits 4000 the engine drops to 3500 then back to 4000 will not go above 4000 rpm. Checked tail pipe very black and a lot of carbon on the driveway under the tail pipe when you rev the engine. Did the paper over the tail pipe to make sure it wasn’t sucking back in (sign of valve problems?) constant pressure and good flow. I wonder if it has the wrong MAF sensor now and if the ECU is the right one for the car?


#2

Did anyone check the fuel pressure regulator? Might have the wrong O2 sensor. Are you using the stock air filter?


#3

Has a check for a vacuum leak past the MAF sensor or exhaust leak on bank 1 been done? If excess air is coming in the O2 sensor for bank 1 will call for more fuel to be injected on that side.


#4

Keith: Yes, we checked the fuel pressure regulator and the system is holding 40 lbs at idle, drops to 35 under acceleration but returns to 40 quickly. Have not ckd the o2 sensor the shop replaced to see if its ok. Yes we are using a stocked air filter.

Cougar: Only 2 injectors are injecting too much fuel, One on left and one on right, middle is working perfectly. Perplexing Question - If the o2 sensor was calling for more fuel on that bank how come all 3 aren’t running rich? Not sure how to test for exhaust leak except by sound.

Question: Does anyone know how to check the VIN number on the engine so we can make sure we have the right components based on the engine?


#5

You didn’t say how many miles are on it, but the car itself is 16 years old, so it’s quite possible the injectors have simply given up and need to be replaced.


#6

So how did you arrive at the 2 faulty injectors conclusion based on a 172 code?

While stating first off I’m on Buick pro, let me propose this theory based on the boost fault. GM, just like Ford, uses a vacuum pod to operate a flap in the manifold which then controls the boost.

The flap is closed due to high manifold vacuum at idle/low RPMs and the engine functions as a normally aspirated motor.
When the pedal is nailed vacuum drops and the spring loaded diaphragm opens the flap which in turn allows boost to build.

The symptoms this car has could very well be caused by something like this so inspection of that pod would be something that can easily be done. Simply make sure the arm/flap move freely (there will be diaphragm pressure) and test the pod with a vacuum source.

The pod has a rubber diaphragm inside (just like a dashboard pod, old carburetor choke pull-off, etc) and at 16 years old it’s possible the rubber has split.
Just a theory anyway and hope it helps.


#7

Thanks for the feedback.

The car has 108,000 actual miles on it.

Replaced all injectors this week with units from Injector Warehouse. Idles a lot better but still running rich on cylinders 1&5.

I determined that cylinder 1&5 are running rich by removing the plugs and checking deposits.
1&5 are wet and carboned bad, the rest have a nice slight tan color and are dry.

My thoughts are that there is a problem in the ECU telling the injectors to stay on too long or there is a short to ground in the ground wire to these injectors.

Need to see if I can find a pin-out sheet to see witch wires I am dealing with and break out the Ohm meter. anybody know of a good used ECU for this car?

Checked vacuum on pots all is good.


#8

Wet and carboned plugs do not necessarily mean an injector problem. Low compression or weak spark can do the same thing.

A quick look shows 2 firing arrangements for this year model; a Type I and a II with cylinders designated differently. I’d make sure wires and whatnot are running where they’re supposed to.


#9

May have found the problem. I went to my local auto salvage yard and bought a used computer that was for a supercharged car of the same year. The computer number was the same as mine but the chip set was different. When I installed the salvage computer, the car would barely run and was showing multiple codes. Pulled the salvage computer out and swapped the chip set with my computer… car started and ran pretty well, road tested and it ran much better, but I think the cat. is semi plugged from all the carbon… may put in a test pipe to see if that solves the problem entirely.
**** Does anyone have the factory chip set code for this car?

Long story short, after 2 shops and a lot of bucks… nobody checked to see if it was the correct chip set and computer combo…this may not be the exact set yet for this car but if it is, then I think I am a lot closer to solving the problem. The car is currently avg. 12.7 mpg a long ways from what it should be getting …
Thanks for the help will post all results so as to pass on the knowledge… I wonder if there are any proformance chips still around for these?


#10

Sounds to me like the engine has been damaged… though the newer computer helped. It could be a shot to see if the dealer or somebody has the software hook ups to check or reset the system.

Now. Some of these older systems would do a diagnostic and reset themselves sometimes could take a few minutes without touching a button… like walk away.

but a 98 olds regency getting what gas milage new? maybe at a cruising speed on the highway but around town is going to be pretty poor. still sounds like head valve leaks and worn lifters or something probably from over heating.

good luck… nice car though…