2000 Bonneville SSEI 142000 miles severe hesitation on light accel. runs great on hard acceleration
have had repairs done at trusted shop with certified techs
replace intake gaskets -fuel pump and sending unit - ftps - purge valve all new vacuum lines and fittings (checked with
smoke machine) - new egr tube and valve. throttle body cleaned and gasket replaced air filter and fuel filter replaced -
02 sensor -replaced map sensor -replaced the maf x2 replaced coolant temp sensor - replaced - coils and wires replaced - ignition module replaced spark plugs are good
gas cap replaced prior to repairs multiple codes showed --- now no codes but still has same symptoms
SEVERE STUMBLE AND HESITATION ON LIGHT ACCELERATION SCAN TOOL SHOWS LEAN CONDITION after all repairs were done maybe worse. can now add stalling to the list. always use premium shell gas. need some help!

I don't see anywhere in the list that the MAF was touched. A bad MAF will cause those problems, because it's the primary source driving fuel richness. WOT ignores all sensors and just pours the fuel into the engine, which is why it runs good at WOT. IF you haven't, try cleaning the sensor wires in the MAF, otherwise replace it. Mine would stumble and die, even after cleaning the MAF...replaced it and haven't had a problem since I've owned the car now.

_________________
A temporary fix does not exist. It becomes a solution until it needs to be fixed again.

https://photos.google.com/album/AF1QipOYkkevV0gKTHc_8Cstuy8yS1Qyx6SiIKeTzuHy

x2 on maf - unplug it and see if it improves.

_________________
poverty forces one to do unorthodox things

2000 SSEi
past rides:
1996 SSEi
1992 GTP
1987 Grand Am

ordered a new maf this will be the third one that I have installed. drove car 57 miles with it unplugged and car ran great---
but showed a lean condition on scan tool bank 1 o2 sensor reads low and does not change much. plugged in maf sensor
and car was hesitating badly jerking the maf sensor was changing on the scanner normal numbers


thanks for input me and the guys at the garage are stumped

aftermarket mafs have a high failure rate - I got one from ebay that lasted about 2 years

best to get Japanese made OEM - I got one from Harofreak - he has a business in bonny parts

bonneville unlimited is the name I believe.

the lean cond. may be caused by no maf signal

_________________
poverty forces one to do unorthodox things

2000 SSEi
past rides:
1996 SSEi
1992 GTP
1987 Grand Am

found another split vacuum line at supercharger flapper replaced it still same lean condition have a new maf sensor
on the way but the one on the car reads good numbers when its hooked up. persistant lean condition baffling us
car runs great without the maf. three weeks and holding. even asked st.christofer for some help, but he didn't show up. my neighbor is a minister and he is performing an exorcism at sundown today, on the Bonneville.

hey red fury you hit it out of the park new maf solved the stumble but now shows P0171 lean bank 1
but the car runs fine. not sure if it is a valid code as the fuel trim numbers at working as are the o2 sensor
numbers. instant fuel mileage is back up too 33 mpg @ 41 mph was fixed at 22 mpg @41 mph
thanks for the response I think the exorcism worked a friend in texas bill

you can:
-propane/carb cleaner test it to find the leak. check the line under s/c snout.

make sure you have the pcv installed and it has an o- ring.

I found a leak by removing the s/c belt to make the engine quite and listening - it was that blocked off hose from on top of the t/b - used high temp silicon adhesive to repair


so this lean trim returns to normal under acceleration?

_________________
poverty forces one to do unorthodox things

2000 SSEi
past rides:
1996 SSEi
1992 GTP
1987 Grand Am

Here's what I don't like about these Bonnevilles, I don't see how you can get a Lean Bank 1 code when the car only uses one oxygen sensor. All that means is that it's seeing a lean condition, no particularly on one side of the engine or the other.

With that being said, I'd take a water bottle, put a pinhole in the cap and start spraying around the intake gaskets, the throttle body gasket, the supercharger ...anywhere that could suck air. If it's leaking, you'll know. Solvents evaporate to fast, aren't safe to use and are just going to make the engine run better. You'll hear water getting sucked in vs. a spray solvent.

_________________
A temporary fix does not exist. It becomes a solution until it needs to be fixed again.

https://photos.google.com/album/AF1QipOYkkevV0gKTHc_8Cstuy8yS1Qyx6SiIKeTzuHy

Good morning. I have the same problem with a 2001 SSEI. Replaced MAF sensor and still same problem. I have been told I need a new ECM (PCM?). Looking for confirmation on that diagnosis, and any fixes that may be available. If replacement is required, I am looking for a place to buy (and program?) a new ECM. Thank you.