mdtoren

Hello gents!

Any help would be very much appreciated!! I've got an 86 tpi motor that I just pulled the egr on and cleaned and now I'm having issues at mid to wide open throttle..there is a lack of power and stumbling/random misfire under those conditions in drive only. In park it revs up perfectly. When I first rebuilt the intake it wouldn't start at all without giving it gas and got codes 33 and 34..I think that was from the throttle body cleaning throwing the min air and tps out of whack.. Reset the idle iac and tps and all is good with start up. Codes are gone.

Here's what's done so far:
Cleaned egr and installed with all new gaskets for egr, runners, and throttle body
Verified all vacuum lines connected correctly
Cleaned throttle body and plate
Reset iac and min air rpms to 450 using instructions from here and reset tps to .5 idle/ 4.5v wot - both iac and tps replaced within 1000 miles. Verified tps voltage steps up correctly as throttle opens.
Verified vacuum reading of 16 at idle, snaps to 1-2 and up to 21/22 with a throttle snap
Verified fuel pressure at rail with regulator vacuum lines plugged at 41psi
Ohm'd all injectors at 16 ohms, verified they are firing with stethescope.
No visible spark arcing to the headers.
Cleaned maf
Brand new o2 sensor with less that 100 miles


I assume being that it's a drive only issue that it's a sensor reading but I'm out of ideas. Help! Really looking forward to getting her to this show Tuesday.

aliceempire

iTrader: (14)

Did you do all that after the problem came up? I'm not too MAF savvy but I'd suspect problems with it.

formula_novice

iTrader: (1)

It's my understanding that stock fuel pressure is 43.5 psi at idle.

mdtoren

Well the project to clean the egr started because I had a popping in my exhaust and a low idle stumble. So I thought the egr might be stuck open, which it was, and leaning out the fuel mix at idle. I cleaned the throttle body while it was apart, everything else was done when it wouldn't start after I put it back together. Could the maF be bad even without throwing a code? Could my idle adjustments be masking the bad maF? The engine is still popping frequently in the exhaust and stumbles slightly at low rpm.

And would the 2 psi make a difference in performance on the fuel? It may very well be at 43..leaky fuel pressure tester..

aliceempire

iTrader: (14)

Yes and yes. That doesn't mean you have a bad maf still. 43.5 at idle is the target range. Can be a little higher or lower. Since it seems lean in drive, find a way to see the pressure gauge while the regulator is hooked up and driving. Pressure may be going too low under load.

mdtoren

With the regulator vacuum hooked up it was reading around 34 psi without load, should I look for a drop from this lower number or should the psi be 43.5 with regulator hooked up also?

aliceempire

iTrader: (14)

The vacuum lowers the fuel pressure, therefore when you open throttle, the vacuum will be less and the fuel pressure will go back up nearer your 41-43psi. If it doesn't you'll need to dig further into your fuel system and you can ignore possible maf problems for the time being.

TTOP350

iTrader: (8)

2 LBS isn't enough to worry about, the problem is elsewhere.

aliceempire

iTrader: (14)

I'm not concerned about the two psi, I'm questioning whether the fuel pump is putting out the volume it needs while under load.

TTOP350

iTrader: (8)

Put a test gauge on it and check the PSI at wide open throttle with a load on it.

mdtoren

Hopefully I haven't losyt you guys, just had time to test it...so in drive the fuel pressure hangs at a steady 33-35 psi when driving, at mid throttle the gauge flutters alittle between 33 and 37psi. With the pedal to the floor it holds steady at about 33-34psi. Turned off car and it bumped up to 42

aliceempire

iTrader: (14)

That MAY be low but not a lot. I would hope to see closer to 42 at WOT. Hard to rule out without testing a known good car. I don't know if I'd be too worried about it being this low as I don't think it would lean it out that bad. At best it's just junk in the fuel filter. But I'd look into maf problems. http://www.aa1car.com/library/maf_sensors.htm
http://chevythunder.com/maf_code_33.htm
http://chevythunder.com/maf_code_34.htm

mdtoren

Well I'm about 100% positive the fuel filter needs replacement..I have the replacement but can't get the damn thing off. I will start digging in on the maf..I suspected that it might be the issue. Thank you for the help!!!!