hey guys this is my first post here so hi all! got a problem with my 85 trans am...violent bucking and surging, poor mpg(20 or less), low vacuum, poor idle, stalling at times, etc. i do have a code 33...but my friends scanner show the maf unit is working to some extent...just wondering if all this is being caused by the maf or if it is possible that the camshaft might be too much...i dont know what is in it now...just got the car in january...please help!!!


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Scott Downs
85 Trans Am
3.73 w/275/60R15
plain firebird nose

 

There is no such thing as a cam to big, just a motor to small. So, either the motor is to small, or it may be one of your other options. But remember.....THE CAM IS NOT TO BIG!!!!



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Joshua Johnston
1991 Z-28
Flowmaster
K&N
305 / 5spd. (Temporary)

 

thanx JJ....this is sometimes true! Forgot to mention that the car is also running really rich...

 

You think 20 mpg is poor? man i get 9

 

well i guess ya got me on that one eighty5transam...lol...its just that the mpg has decreased since i first bought it...was like 27...

 

Yea I had the same problem not too long ago and it turns out my favorite gas station had gotten some bad gas or something cause after I burned 3 or 4 tanks of Exxon it went away. Have you done a full tune-up on it?

 

Voyager, the cam is "probably" not too big. All the symptoms you stated point to that code 33. Check intake ducting and make sure everything is sitting right and square. Then check the MAF relays and make sure they are good (I'd just put newones) and also make sure the wires going into the relays are not rubbing against each other.
Rick

 

thank you F22Raptor I'll check on that tommorrow, i've already checked the ductwork...all seems well on that end....

 

ok i changed out the relay for the maf....no change....just remembered something, to get the car to run decent i have to set the timing pretty high..not sure of the exact amount but probably around 15-18 degrees...also not noticing much advance when i rev the motor with the timing light on it....what gives???

 

damn, i dont want to scare you but...ECM or MAF wiring could be the problem.

 

if you have a big cam and your car is bucking
alot and you run an automatic chances are your
stall converter is stalling to low, and in
over drive whin it locks up at low rpm
it will really jerk alot.
change to a higher stall converter.

check out my simple page at:
http://darcom.home.texas.net/

 

When I had a code 33 I replaced my MAF and it fixed a stalling and poor idleing problems.

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission
Borg Warner 7.75" 9 Bolt Rear End

Current Mods: LT4 HOT Cam, Comp Cams 1.52:1 Roller Rocker Arms, Edelbrock TES 1 5/8" Headers, Hooker 3" Aerochamber Cat-Back System, Performance Resource Chip, Accel Ignition Coil, Cap, Rotor, 8.8mm Wires, K&N Filters, JET TPI Air Foil, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET (w/o LT4 cam): 14.32 @ 97.7mph
(corrected for elevation)

Soon to Come: 7.625" 10 Bolt with 3.42s and Accel TPI Intake Base

 

oops, didnt read closely enough. you said the MAF sensor is working "to some extent". thats not always good enough. id bet on the sensor being junk.

 

Your symptoms are classic conditions that are caused by a blown fuel pressure regulator. The fuel getting past the diaphragm in the fuel pressure regulator and being sucked into the intake via the vacuum line will cause the rich conditions and the bucking and stalling and also hard starting. I personally have fixed this problem on more GM multiport fuel injection equipped cars than I care to remember including quite a few TPI's and LT1's. Check that out....!!! Laterzzzzzzzzz

[This message has been edited by Matt87GTA (edited April 01, 2001).]

 

how do i check that fuel pressure regulator?

 

Pull the vacuum line off of the Fuel Pressure Regulator while the car is running and see if any fuel comes out of the vacuum port. If fuel isn't coming out of the vacuum port then try pulling some vacuum on the port (put the vacuum line close to the port to create a vacuum in the regulator, then see if it sucks any fuel out of the regulator). If no fuel comes out of the regulator vacuum port at all with the car running or with the fuel pump running and the car off, than I guess it is something else like a leaking cold start injector. Test the regulator first though.....

 

ok i checked the regulator but didnt see any fuel in the vacuum. i had my friends scanner hooked up tonite and got the following info from it...
idle @ 1000(does that with scanner attached..normal is about 750)
IAC=16
INJ PULSEWIDTH= 2MS
CLOSED LOOP
MAF=1120 GR/SEC
MAT=139
OS2=89MV
OS2 CROSSCOUNTS=156
PROM ID=7741
TPS=.58
EXHAUST O2=LEAN
EGR DUTY=0%

READINGS AT 3000 RPM(IN PARK)
IAC=32
INJ PW=2MS
CLOSED LOOP
MAF=4866 GR/SEC(FLUNCTUATING THOUGH)
MAT=153
O2S=333-710(FLUNCTUATING)
O2 CROSSCOUNT=46-254(FLUCTUATING)
TPS=.84
EXHAUST O2=RICH/LEAN
EGR DUTY=30%

hopefully someone is willing to go through all this and will be able to help me pinpoint the problem(s).....please!!!!
Scott

 

by the way when the scanner was attached we noticed that the O2S was reading about 86 mv while driving down the road at about 70....is this right?

 

Those O2 sensor readings look a little lean to me but if you are logging crosscounts than the O2 sensor must be working decently and the ECM is adjusting the fuel from rich to lean and vice-versa while it is reading the O2 sensor. O2 sensor readings can be misleading at times because the ECM will sometimes see a problem and try to compensate for it and screw up the O2 sensor readings in the process, many times even giving a 'false' O2 sensor code. Try checking for a vacuum leak in the intake system. Make sure all bolts on the runners and Throttle body and clamps on the air intake hoses are all tight. Your problems still sound a lot like a fuel leakage problem to me though.

You can try installing a fuel pressure guage on it and checking to see if the fuel pressure drops after the engine is off. You will need to pinch off the feed and return fuel hoses right by the brake master cylinder when you do this to ensure that you are sealing off the fuel system that is on the engine from the rest of the system. The best way to do this is to prepare to block off those rubber lines with hose block off clamps (vice-grips will work but be careful not to trear the fuel lines). Than have someone key the car up but don't turn it over. Watch the fuel pressure guage and clamp off both lines when the fuel pressure reaches a steady level (this number depends on the regulator but it should be between 42-48 psi). Now it's just a waiting game to see if the pressure drops. If the pressure drops real fast (like within a few minutes), than you have some kind of a leak in the system, either an injector or that regulator. Sometimes the regulator will be sneaky and won't show up as leaking until you really pump the pressure up on it and hold it like this test does. If you have found a leak, take the fuel rail off with the injectors still installed and repeat the test and look at the nozzles of the injectors to find the one(s) that are leaking.

This type of diagnoses is an involved project and is difficult to do when the car is in your stall - much less over a message board!! But i am just giving you some of the techniques that I have used (I wrenched at a Chev dealer for a few years).

Hope that helps......!! :}

 

thanks Matt i will do that this weekend...i think i found a good part of my mpg problem tho...changed out my 160 thermostat for a 195'er...big improvement there...also found out that my coolant sensor to the ECM of by about 35 degrees...will fix soon....thank you for all your help, and i'll let you know the results of the leakdown test....

 

any idea's about the timing not advancing much?...max is maybe 10 degrees...

 

Are you setting your timing properly? Are youd disconnecting the single lead wire and then setting the timing to 6 degrees, and then plugging the wire back in, and then turning the car off? The wire is on the passenger side, and breaks out of the main conduit. It's a tan wire w/ a black stripe.

 

That's exactly what I was thinking!! You said that you just got the car back in January and I could be wrong, but I'll bet this is your first thirdgen....at least fuel injected anyway!! If you don't unplug the wire that "90Iroc" is talking about it'll seem like the timing is pretty high!! It's like unplugging the vaccuum advance on a carb when you set the timing....this is the same way, only it's an electrical wire you unplug and not a vaccuum line!! Carbed cars have vaccuum advance...TPI cars have computerized advance!!!


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1986 Trans AM
305 TPI
Well over 200,000+ miles (speedo/odometer non-funtional! Odometer reads 142,000)
4 Wheel Discs
9 bolt Borg Warner Rear (2.77's....oh joy) :P
Completely Stock
Soon to upgrade to a 355 TPI, Stock TPI ported, 24#/hr SVO injectors, Hedman Shorty Headers, Dart Iron Eagle heads or GM LT4 heads, XE262 Cam ground on a 114 LSA, Moroso Blue Max Plug Wires, external MSD Blaster II Coil and an MSD 6-AL Box!!
Current project: Keeping my 305 running until I get my income tax returns!