Intake backfire/pop...

[Cakes]

Last night on the highway about 55mph I gave the car a good romp and it shifted to 3rd, stumbled, backfired through the intake and I noticed a puff of smoke from the exhaust(dont know what color it was as it was dark). Noticed O2s were 800 w/ 2.8 kr.(due to 18 lbs of boost) Later down the road I did the same thing except I kept the boost at 15 using the throttle (maybe half throttle or so) I noticed the car was sort of "chugging" and not accelerating much at all, then gave it WOT and it stumbled again but no backfire and it took off. I did notice however that when I go WOT my boost will shoot to 20 and then stay steady at 18. I have the wastegate bypassed and I am usinbg a Parker gate valve to play with boost(Cottons setup he sold me) Could me running 18 lbs of boost have caused this problem? It was damp last night and I didnt know if it would have effected anything like that? I ohm my coil pack and each was 13.1 ohms(x1000). I had fuel pressure set to 44 psi line off and I was running 94 SUNOCO. Maybe someone can suggest something on what my car is doing? Thanks!

 

[Cakes]

Today doing a similar test except with boost down to around 17 and fuel pressure to around 45 psi line off, I noticed at 10-15 psi of boost the O2 voltage never went above .050 (yes it was that low) This leads me to believe that I have a faulty O2 sensor, but I am not positive. When the computer sees WOT the O2 sensor goes "dumb" and does not contribute to the enrichening process I could see why under WOT the car would have OK O2 readings after a WOT blast. What I am concerned about is if there is another problem lying underneath(I have been trying to track down a low MAF reading...180 at WOT). Maybe this new info can help someone suggest something. Thanks!

 

[Cakes]

Anyone?!?!

 

[NASSTY]

Have you changed the o2 sensor to see if your readings change?Is there much fluctuation in your boost gauge?

 

[Cakes]

I have a GNX sensor coming to me. When I am holding the throttle between 5-15 psi (and not at WOT) my boost gage will hold steady and not bounce or anything. During this my O2s stay at .050 milivolts or below, MAF readings are aroung 115 gps or so, BLMs are around 140 or so. I did notice that the whole time this was occuring my O2 readings are staying at the .050 level and not changing much(Cross counts not moving???) I didnt check cross counts at this time. Also I am not runinng a PCV valve, just an ATR check valve(I have a AC PCV valve on order as well...going to run it inline) Maybe this info can help some.

 

[RealFastV6]

Try another MAFs.

 

[Eric Stage I]

The MAF reading of 180 at WOT is a huge problem. Your mixture will be way lean. At 17-18psi, you should be seeing 255. If the reading is that low at WOT, then its probably too low in the midrange also. That could be why you not getting an O2 reading in the 5-15psi range.

Eric

 

[Scott231]

I fully agree with Eric that the MAF reading is indicative of a problem. You need to test the validity of the MAF first. Since you cannot run down to the Buick dealer for another one I'd suggest you swap MAF sensors from a known-good running TR motor and check the readings on both cars before and after the switch. You could simply have a plugged-up air filter, a hole in the MAF pipe before the sensor (assuming your setup has one), or some bad turbulence also prior to the MAF sensor.

Don't assume you have a bad O2 sensor and run out and buy a GNX sensor (ooops you already did that)...prolly a waste of money. If you are receiving a low reading at WOT, that points to a problem in the content of the exhuast stream, not a bad sensor. (Do you really think GM just added sensors so they are something else that can go wrong and require your good money to replace on a periodic basis?) Your BLMs being so far away from 128 also point to a bad air fuel mix.

If the sensor reads normally at non-WOT positions, then it is a good sensor. Sounds like you may also have the infamous header leak. That leak always causes low O2 readings at WOT as additional oxygen is getting into the exhaust stream. Another contributor to a weak O2 sensor reading at WOT is a weak ground, but that is likely when you are constantly getting bad O2 readongs (not just WOT).

 

[Cakes]

Hey Scott231 Thanks for the reply. I have a 3" LT1 MAF sitting in the back seat of my car right now. I am at college right now but I came home last weekend hoping to buy a translator from Cottons (he is 5 minutes from my house) but he said he didnt have any so I wasnt able to purchase one but I will the next time I am home. As far as a clogged air filter, the big mouth is less than 3 weeks old on the car so I HIGHLY doubt thats a problem. And I am pretty sure all my connections are tight before and after the turbo.

Now onto the MAF side of things. To let you know I have a Kirbans remanufactured unit on the car(found the paper work in the glovebox) It is of the correct style (non hour glass) but I just recently noticed it wasnt going to 255 gps. Now that I know my O2 readings are way off during non-WOT situations it makes sense that my MAF is not calibrated correctly. At WOT even though my MAF says 180 it doesnt mean a whole lot since I am assuming my chip locks MAF at 255 under WOT. The reason I am assuming that is even though my MAF readings at WOT are 180 or thereabouts, my O2 numbers are right in the correct range (high 700s, low 800s with minimal knock running 17 psi) Is my theory bogus or could I be on the right track?

PS I dont mind spending the money on the GNX sensor since its one thing I havent replaced on the car since I bought it last March (I know I have a Bosch in there now)

 

[Scott231]

Originally posted by Cakes
As far as a clogged air filter, the big mouth is less than 3 weeks old on the car so I HIGHLY doubt thats a problem.

OK...but was the MAF problem there before the addition of the Big Mouth?

I have a Kirbans remanufactured unit on the car. It is of the correct style (non hour glass) but I just recently noticed it wasnt going to 255 gps.

Since there is no such thing as a remanufactured MAF, I would be suspect of the part. Please report the part number of that MAF to us in this thread.

Now that I know my O2 readings are way off during non-WOT situations it makes sense that my MAF is not calibrated correctly. At WOT even though my MAF says 180 it doesnt mean a whole lot since I am assuming my chip locks MAF at 255 under WOT. The reason I am assuming that is even though my MAF readings at WOT are 180 or thereabouts, my O2 numbers are right in the correct range.

You still haven't addressed the possible header crack issue...and if the O2 sensor is reading correctly at WOT...why are you replacing it?

 

[Cakes]

Scott231, the MAF problem was there before the big mouth installation, so I am ruling that out. I dont understand why you say there is no such thing as a remanufactured MAF. I have the paper work in the car. Im just going from the paper work I found. I am not able to get a part number off the car since I am at school but I know for sure its an AC Delco unit(case) and its from Kirbans. Im replacing the O2 sensor for peace of mind. I dont have any repair records on the car(just parts reciepts) so I want to have a base of where I can start. Once I know everything that has been done and when it has been done I can keep a log for myself. My header crack has been welded at one time. I can see the weld very clearly although it is not to say it doesnt leak once again. From what I can hear there is very little if any exhaust leak from that region.

Just to clear things up, I dont have low O2 readings at WOT. I have them BEFORE WOT. When I say between 5-15 psi I mean when the computer doesnt even go into enrichment mode.(i.e. my scanmaster doesnt even record these readings so it must be less than 3.0 TPS volts). Hope this can help some.

 

[Eric Stage I]

Email Jay Carter and see if his chip locks MAF to 255. That would solve that riddle.

Eric