87 Vette Owner

Hey guys -

I've been doing a bunch of tuning and data logging over the past year and a half. Recently, every now and then I get a strong hesitation and/or backfire while going from very light throttle to full throttle. It doesn't happen when I hammer it, but when I am somewhat slowly pressing the pedal down.

I took a look at my data logs and found that the MAF voltage reading momentarily drops to "0" when this backfire / hesitation occurs (and then comes back up). Until recently, I've never seen that in the data log (and hadn't encountered the hesitation / backfiring either).

Could this be the beginning of the MAF sensor going bad? There are no loose / worn wires, connections are clean, etc. The MAF is the original from 1987, though I removed the screens and heat fins several years ago (never had any issues until now).

What do you think?
Thanks!
Dan

__________________
1987 Corvette 383 ci small block

TPIS Mini Ram, 58 mm Holley TB, Accel 30 lbs. inj.
AFR 195 heads, 1.6 Howards Cams roller rockers
240/240 @ .050, .580 lift, 112 lsa Howards hyd roller
Eagle forged rotating assembly (approx. 10.0:1 comp)
Walbro 255 fuel pump / Racetronix wiring kit
1 3/4" TPIS ceramic coated headers, Borla mufflers

Blue tag ZF 6 speed conversion (orig. 4+3)
D44 w/ 4.10s , 5 point roll bar

AutoProm, TunerPro RT, LM1 Meter

RBob

With the engine idling tap on the MAF sensor. If it stumbles or such then the MAF is on the way out.

RBob.

__________________

www.DynamicEFI.com

'92 Camaro in Dark Green Gray Metallic

87 Vette Owner

Thanks RBob - I'll give that a try this afternoon. Assuming it is the MAF sensor, where is the best place to get a new one?

Thanks!
Dan

87 Vette Owner

I tapped on the MAF while the engine was idling - there was no effect; the idle stayed steady.

I still think it might be on it's way out...

RBob

It may be the TPS is going out. Sounds strange but there is something that keeps telling me that it is the TPS. Part of it is the slow throttle movement. This reeks of TPS problems.

A bad spot in the TPS can have the ECM thinking that the driver lifted off the throttle. It sees it go from 22% to 0%, the ECM will cut back on the fuel.

It can be tought to test a TPS for bad spots. But it may be worth looking into as they are less expensive then a MAF.

RBob.

87 Vette Owner

Ok - I'll get a voltmeter on the TPS tomorrow and double check it. The data log does not show any drop at all in TPS voltage though; it seems to be reporting accurately.

Thanks!
Dan

Oldies

Hi, Check out www.c4vettes.com for useful Mass Flow Facts - i hate this MAF sensor problem... my 85 Z28, 5.0L, H.O., TPI gave "no start" problems; then its fine; then no starts; then dies at the intersection, or going up a small grade; then restarts; or, press the pedal down and nothing happens; release pedal, it comes back; or drives choppily at 35-45mph; all with eng ck light on, all code 33! Not solved yet, even nos bosch unit; bought pigtail harness, not arrived yet from tpi-parts, eBay. Good luck!

pandin

check out:
SIA Electronics
$68.00 to fix.
fast turn around.
They can test and advise.

I had no luck with AZ.
2 maf - two bad, one read way low 183 gr/sec @ wot, the other died when hot also read low. The SIA one reads 232 gr/sec @ wot.

AZ returned my money.
Then they kept the core (it was dead) but they gave me $80.00 for the core. Glad I had extra mafs.

pandin

Check out the relays, some are better then others.
I use the fan relay replacement for both the maf power and burn off, it is heavier duty and the same price.