SOO here are the particulars... 92 z28 350 tpi motor. has a bbk 52mm tb slp runners and i believe thats it. dont know because all of that was done before i got the car. Has been running fine up until a couple months ago when i started to get uneven acceloration. Not stumbling, the power would just progressively surge in different spots in the rpm range...then a couple weeks ago the car started stumbling and missing very badly but only sometimes. other times it would run smooth for a while...anyways it comes and goes but it is getting more and more freaquent. It is especially bad under 1500 rpm. from a stop. the car will start kicking and bucking hard and sometimes ill hear the engine stop firing for at least a full second if i give it throttle while its doing this. and it will sputter and every.

The car starts very easily and with no hesitation and idles fine although i can hear little sputters and misses but the idle is steady and only sometimes gives a slight surge. I can freely rev the motor when its in nuetral. Ive gone over all the vaccuum lines i can find. Ive changed the egr valve because that was throwing a code. now the code is gone. Ive changed the tps and the o2 sensor.

Now all of these things have seemed to have changed the characteristics of the problem but the problem seems to get worse sometimes than others...hard to explain. ive also tried messing with the IAC which isnt that old itself and set the minimum air and all but that made it worse. I tried adjusting the tps sensor because according to data master it was at .9 volts at idle. I couldnt get it any lower than .78 though by twisting the sensor.

I dont think the spark plugs are arcing because ive tried the shut the lights off and look for sparks method and see nothing and the wires are msd 8.8's which have a pretty think sheathing on them, and i changed the plugs and cap and rotor at that time too. i do have an msd box installed but when i bypassed it there was no change...................soooooooo im lost and am losing hope quickly. i hope i didnt over explain anything but i wanted to get the whole story out. ok..HELP ME!!!! please!!!!

 

Try using paragraphs or spacing. If people can wade thru a 100 sentence paragraph easier they tend to respond more.

When u say sputter is it a complete cut out or is it stumbling badly?

Lots of things it can be, but u need to actually try diagnosing instead of throwing parts at it and getting frustrated.

check and test the fuel pump and injectors, do a leakdown test.

Stock injectors should ohm out very near 17ohm, less than 12 is junk per GM.
If they are bad, they can overheat the drivers in the ecm and cause them to overload and then come back on when they cool down.

Clean and tighten the cylinder head grds located on the rear of the pass cyl head.

Get the ignition module tested 7-8 times in a row(will show up under heat, but no guarantee.

Put a vacuum guage on the motor, should be a clean steady needle around 19 inches or so if its purely stock.

Test the pickup coil in the distributor, should be between 200-900ohm and not shorted to grd or each other. AC voltage should be .5 give or take.150.

Report findings after that and we can work out more.

Also check the exhaust for restriction.

later
Jeremy

 

it will completely cut out if i lean on the throttle just enough but most of the time its a pulsing stumbling. tested the tps for smooth functioning so no spikes. ill get my multimeter out and start testing. any way to test an IAC?





youll have to turn your speakers way up to hear anything very well. but basically when i zoom in on the tach and it stays steady before you hear the trans downshift its cutting out. im leaning on the throttle to the point just before it takes it out of lock up so im putting a load on it at that low rpm. dont know if the vids will help or not but i thought id try.
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i know there is wind noise but a lot of that static/wind sound is actually the sound of the engine

 

ok well i checked my fuel pressure and it was sitting at 30 psi with and without the vacuum line attatched to the fpr. and when i rev there is no pressure increase with the fpr connected. soooo i think that narrows it down to a plugged up fuel filter or a bad fuel pump. anyone want to make bets?

and im guessing there is no good way to test a fuel pump unless its just completely not working? are there any relays or ground for the pump that could be causing this?

 

Sounds like u found it.

U can do a volume test with it into a coffee can or the like with the rails unhooked and the relay jumped.

If its as low as u say, 99 to 1 its time for a new fuel pump.

I would suggest a Walbro, but make sure u get a real one, try Full Throttle on ebay, but watch other ones on their good deal or not, there are fake ones floating around.

later
Jeremy

 

i was thining about doing one of the racetronix kits. Anyone have any good experience with one of those?