Please Help! Grumpy? Anyone?

[Guest 73TPIZ]

My setup: '86 305 TPI with Crane 2-5k cam, 1.6 rollers, L98 alum heads with some port work, smoothed lower intake, stock runners, cleared and smoothed upper plenum, homemade ram air setup, adjustable AFPR, and block huggers with cutouts.

 

It runs fine with the 48mm TB but I installed a 58mm and it runs fine for a mile or two and then gives code 33 (MAF High Air Flow). I know the 58 is big (even for 350) but i may upgrade to 383 later and thought i'd experiment early.

 

My A/F ratio meter shows ok till i get the trouble code and then the ecm shuts fuel back to idle amnt and the A/F meter goes BELOW lean. Clear the memory and she'll run fine for another mile or two (even has good throttle response/driveability) and then repeats. Re-install stock TB and runs fine.

 

What's strange is this comes with only part throttle usage for the mile or two (no WOT). How can the air flow be too high at part throttle? After trouble code trips it still pulls good at WOT with good A/F ratio (ecm ignoring MAF at WOT which is correct). ECM's in closed loop so that seem's ok.

 

I know you can get a supercharger for say an '88 TPI (mass air) which would flow way more air. Do they change those to speed density or have a chip that won't give the trouble code?

 

Two things i've tried is buy a GM chip for a 350 in case it gave larger air flow ranges. My conversion book says the chip is only diff in '86-89 305/350 motors (ECM, MAF, TPS, etc, are same part #). The other thing i did is move the IAT to just before the TB just in case the IAT in the upper plenum was a little too warm and the MAF was having trouble holding the wire at a 75 deg delta with the cold air from the ramair rushing in. Neither move made any difference.

 

TPS set at .62 V currently but have had it everywhere w/in .54 +.08 V with no change.

 

Sorry this post is so long but i'm at my wits end (short trip). Future changes may include a Haltech E6GM ecm but i hope someone can tell me how to avoid it for now and run the 58mm with stock ecm.

 

That mile or two before the light comes on is addicting. i can just feel its half a tenth faster. yea right . but it does pull good and A/F ratio looks good till then.

 

I really don't want to be the only guy on the block with a $300+ BBK paper weight! Thanks a bunch for any help guys.

[grumpyvette]

http://www.c4vettes.com/ecm.htm

 

heres what the chart says

 

1985-1990) Inspect intake system for leaks, Inspect for vacuum leaks, Check MAF connector and wiring, Check MAF for open using digital Ohm meter. Possible ECM failure.

33 (1984) Check vacuum hoses. Check wiring to sensor. Change sensor. Check connections at ECM.

 

now logically the engine pulls EXACTLY the same volume of air thru the throttle body at any rpm reguardless if its a 58mm or 48mm, are you useing the same sensors (IAC,TPS,MAF) on BOTH THROTTLE BODIES ?, are all the same vacume lines hooked up exactly the same in the same places? and have you checked for vacume leaks , I have a BBK 58mm throttle body on my 383, the maf sensor gave me fits for several hours once and it turned out that the bolts holding the stock sensor securely were too long to correctly tighten the BBK throttle body firmly to the front of the plenum and seal the gasket correctly. is the IAC manifold under the throttle body sealing to the throttle body lower surface?, personally Id try swapping the bbk throttle body to a second car, and see if the problem moves with that particular throttle body as a test

 

if all else fails get a copy of chevy TPI fuel injection swappers guide, S/A DESIGN BOOKS has a good trouble shooting guide,

proble causes are TPS set wrong

idle to low, throttle open less than 4% for over 6 seconds

a open connector on ckt 470, swapping sensors one at a time with a known good vehical is a fast way to check suspect sensors

[Guest 73TPIZ]

Thanks Grumpy,

 

Since i can put the stock TB back on and it runs ok would seem that the MAF is fine and the ecm is fine but who knows. I'm switching the IAC and housing each time (3X now) and using the same gaskets and all the TB bolts seem to tighten up. I was thinking if i had a leak past the MAF that my A/F meter would be lean and maybe i'd get a code 44 for lean exhaust but 33 is all i get.

 

A buddy of mine has an '88 GTA with the same TB so maybe i can talk him into swapping some parts (TB and MAF) for troubleshooting.

 

On a side note, will we be seeing you at Reynolds this fall? I'm sure we'd all like to meet the legend behind all the great advice/info. Bet we'd even chip in gas money . I hope to have my 8.8 solid axle swap in by then so i can run DR's or slicks and not spin as bad as last time. I get consistent 1.8-1.9 60fts on good nights at my 3 local tracks on 245 street tires but couldn't get below 2.1 at Reynolds.

 

Anyway, thanks for the info and take care.