Pontiac 97 Bonneville Air Flow Troubles

[leonard89]

I am having some troubles starting on my Pontiac 97 Bonneville. I have plugged it in before and the computer always gets me some Mass Air Flow codes. I replaced the Map sensor, the Maf sensor, Cranshaft sensor, Throttle Position Sensor and still the same. Sometimes when I drive it for 30min or more and I want to go back 15min later it won't start. Then I have to let it rest for 2 hours to drive it back. I also replaced all the Spark Plugs. It makes a funny noise and sounds like exhausted when you just start driving it. It may stop working in the middle of the road. I can feel the engine taking aire somewhere when you just start it and untill you don't stop hearing that sound it is not save to drive it.

[carriedi]

have you done an exhaust back pressure test? Check to see if the exhaust is plugged up.

why did you replace all those parts?

[leonard89]

No, I have not done a back pressure test before. First time l checked this issue with a mechanic he said it was a vacum problem and I had to replaced some sensors.I did it but still have the same problem.I've heard some many opinions but none of them seem to be right.

[carriedi]

a backpressure test measures the pressure in the exhaust. If the engine cannot get the exhaust out it affects the amount of air it can take in. Also, if an engine runs rough it can set a maf code.

here's the thing, codes stored in the computer memory are not what is wrong with the vehicle. Codes are for what the engines sees as out of spec. You have to find out why the part is out of spec. Example: An O2 sensor code for running lean does mean you have a bad O2 sensor. It means the computer sees the engine is running lean because the O2 sensor says so. You have to find out if the sensor is correct and you have to find out why it is lean or if the O2 sensor is reading incorrectly.

Fuel pressure could cause a problem of dying and not restarting right away. Have you checked your fuel pressure to see if it is up to spec? (and stays there) 48 - 55 psi is the spec.

do you know what the actual codes were from before? and do you still have codes now? Are they still the same?

[leonard89]

Thank you man for all information you gave me. No, I haven't checked the fuel pressure. The first time I plugged this car in I got a P1106 and a P1108 code. I have to plug it in again to see what happens.What do you think about those codes?

[carriedi]

P1106 is for MAP intermittent high voltage. P1108 is for BARO to MAP comparison to high.

after getting codes like these I would look at the data stream and see what those reading are doing. After replacing all those parts did you clear the codes and drive the vehicle and see what codes return if any?

[leonard89]

Hey man today I checked the fuel pressure and I could not get more than 20psi.I have another question.As you know the main problem I have with this car is that if I drive it for 10 or 20min and then I try to go back it won't start.It happens the same if you take short trips wich means that you have to turn it in and iff several times.

[leonard89]

So what is the relation of all this problem with a low fuel pressure?

[leonard89]

And why do I have to wait at least 2 hours to get the car running again and stable?

[carriedi]

low fuel pressure from a bad fuel pump works a couple ways. You don't get enough fuel pressure at start up so the engine doesn't start. If you cycle the key a few times before you try to crank the engine (turn on the key so the dash light turn on but don't start the engine) each time you turn the key to the run position the fuel pump should cycle and build up fuel pressure. But if the fuel pressure is low because of a bad pump it will most likely get worse until it leaves you stranded. Won't start again. Sometimes banging on the bottom of the fuel tank will shock a motor to run for a while. Just like banging on a bad starter and having it start to crank the engine over again. Sometimes it works sometimes it doesn't.

Some fuel pumps will work better when they are cold but when the pump heats up is either slips or binds up and the pressure decreases.

[leonard89]

Well it seems to be the fuel pump so I am looking for it on ebay and other sites.Could you please tell me which pump would fit ne better and what accessories must go with the pump to have everything tide up?.Thanks

[carriedi]

it is recommended that you do a fuel filter when you do a fuel pump. You have to check to see if your fuel pump comes with the strainer. If it doesn't you should get the strainer to go with it. If you get a fuel pump from a reputable parts store it should be ok. Like I said though, ask if it comes with a strainer. Buying it off the internet, who knows what you might get.