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97 Riviera High negative fuel trim it's good when accelerating but when I let off the gas short-term always -14.8

Liver lips

New member
13
5
3
Minnesnowta
Buick Ownership
97 Riviera supercharged 01 Park Ave Ultra. Had 87&84 century 97 Park Ave Ultra 97 LeSabre
Replaced everything in the fuel system at least once new Hardline new hard plastic hoses replaced them again with fuel injection hose because I was told it had to be a restriction in the fuel line well there is no restriction I think I would have got it all by the third time but I replaced the damn lines anyway new injectors new fuel pressure regulator and the old one wasn't bad because I put it on my Park Avenue Ultra and it works fine new fuel pump new vacuum switch in the emission system it's after the purge valve I guess that's only a 97 thing, new plugs new wires new first O2 sensor but it reads the same as the old one new used boost actuator. The ring on the gas tank what is rusted out so I made my own ring and it seems to be sealed. when I do a fuel pressure test key on engine off everything is nominal drops to pounds the first 15 minutes and I have30+pounds of pressure yet an hour and a half later. when I bought the car I knew it needed a little work but I didn't think I'd be chasing this demon for months this is my 4th supercharged 3800 and I've never ran across an issue like this before here's another thing it does okay if I drive with a fuel pressure tester hooked up my pressure is directly related to my foot pedal so if I give a gas my pressure goes up I hold it there my pressure stays steady I give it more gas then pressure goes up more i let off goes back down I mean I can blow hoses off if I want to I have probably six times I've Been Told the only thing that will make you build pressure is a restriction or your regulator. Now I've done a fuel pressure after I did the fuel pump and we did the lines again this weekend but I haven't driven with it on. now I am kind of suspect of the cat okay I'm pretty sure the cats bad noticed the guy before me drill some holes in the muffler though if I plug them it doesn't seem to make any difference but the cat fails temperature test and my O2 sensors we're following each other but I hook a pressure gauge up to it and it says it's good I drilled a couple holes before the cat seems to run a little better and my second O2 sensor is little more independent but by -14.8 still is haunting me. I'm thinking about just unplugging everything until something changes that 14.8 I've even ran it without the O2 sensors plugged or maf in same stuff. I also bought a cheap eBay maf sensor same thing. I've even stolen the throttle position sensor map sensor EGR out of my brother's supercharged Regal just to try them. no change. To me it kind of seems like the opposite of a vacuum leak would it be a boost leak? and wouldn't that show up when when I do a smoke test on the vacuum system? There's not a lot of information on fuel trims and supercharged vehicles. Is there maybe a rollover check valve thingy in the tank that might be clogged? I would think it would be integrated into the fuel pump but maybe not I I've been wrong before. I replace some other stuff too I guess I just can't remember it up top of my head. Oh yeah I've taken the whole emission system off blew it all out. no change except I don't catch a wiff of old gas smell now and again anymore
 

LARRY70GS

Full Member
2,142
124
63
Oakland Gardens, N.Y.
Buick Ownership
98 Riviera, 70 GS455 Stg1
Negative fuel trim means the engine is running rich, and the PCM is pulling fuel to compensate. The PCM uses data from the MAF to set up the fuel injection. Cheap E bay MAFs are unreliable. I learned the hard way that you either use AC Delco or Hitachi MAF's. If you have access to a good scan tool, then look at what the MAF is telling the PCM. Usually, when the MAf goes bad, it tells the PCM that there is more air coming into the engine than there actually is. The O2 sensor says too rich and the PCM pulls fuel resulting in big negative fuel trims. A rule of thumb on a MAF's air flow rate at 500 rpm is 1 gram per second per liter of engine displacement.
 

Liver lips

New member
13
5
3
Minnesnowta
Buick Ownership
97 Riviera supercharged 01 Park Ave Ultra. Had 87&84 century 97 Park Ave Ultra 97 LeSabre
I got a Chinese tech 2 on the way first one I got damn near started a fire I left the dang thing plugged in and for some reason I ended up being able to take a smoke break at work early went out to my car and there is a thing was smouldering away my car stunk for a week and a half so now I know unplug the dang thing if you're not looking at it I had it maybe hour and a half but it's taking them a good month before they sent confirmation that they sent a new one to replace it. I had to threatened to get PayPal involved to get them to replace it. Anyhow according to my Harbor Freight scan tool cheap MAF sensors reading the same as my other one so I have the original one in yet. Yeah I know I should know better but I guess wanted to give China another chance. I bought some O2 sensors from eBay while ago and I put them in the car and magically my first O2 sensor read a perfect 4.5 every time all the time. A resistor disguised as a o2 sensor. With that tech 2 they have the technology part of it down but they need to work on the quality control and workmanship it looked like they gave a soldering iron to an elephant P1010096.JPGP1010103.JPG
 

Liver lips

New member
13
5
3
Minnesnowta
Buick Ownership
97 Riviera supercharged 01 Park Ave Ultra. Had 87&84 century 97 Park Ave Ultra 97 LeSabre
Well pulling MAF sensor plug didn't really do anything so I figured I'd keep pulling plugs until my -14.8 went away I left maf unplugged and pulled the first O2 sensor 2 and it ran like s*** so I plugged in 02 sensor again and it still ran like crap so I plugged in MAF sensor again still running like crap then just for fun I pulled the egr and now I just think it's mad at me but my pressure seems to be staying the same now so what's worse engine that runs decent with climbing fuel pressure or one with good fuel pressure that runs like crap?
 
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