88 NA, auto to manual conversion, rebuilt: revving problem has me stumped after aweek of fiddling and searching

well, for the first few weeks following my manual swap everything was running well (too well actually... got a serious ticket in an abandoned parking lot) until i suddenly started to be unable to bring the revs over 6800 RPM and my idle started to get flaky.

it pops and hesitates at several different points above about 5500 RPM.

here's what i've checked:
-changed plugs (leading plugs were caked with brown/grey soot and trailing were
covered in carbon buildup)
-my aux. ports are opening
-tps is set and is at 4.5 at WOT
-timing is spot on
-all plugs fire

in neutral it revs smoothly almost to 7k, but still pops and sputters just around 7k. i'm leaning towards lack of fuel because if i'm coasting at high rpm (3.5-5k in say... second gear, and then floor it, the engine sputters and barely revs up until i let off and try again. i don't know whether to do a bunch of re-grounding or to put in a fuel pressure guage.

 

Are all your injectors pluged in good? and is your o2 sensor plugged in?

 

that was fast... they've got new rubber grommets/rings and last i checked they weren't unplugged... i'll double check though. O2 looked fine earlier today.

 

well, got a few hours to do some measurements and negative battery post resistance to some chassis points sucked so cleaned up the post/clamp, but i'm still getting misfires above 5k. next chance i get i'm cleaning up all the grounds i can get to.

one thing i thought was odd is that when measuring the voltage to the pump (at the connector in the rear hatch) it would fluctuate steadily between 9.5 volts and 11.8. no idea why unless i have a bad connection or the pump is effed. anyone know why this would happen?

 

fuel pump resistor relay

 

all of your issues point to fuel delivery, including your plugs. The voltage @ the pump is WEAK. IMO I would fix that first.

 

thanks, i was uspecting fuel delivery too

this is by the clutch master cylinder, correct?

i'll swap it out tomorrow and put an under-hood fuel pressure guage in... what is ideal fuel pressure? 60+ psi?

 

well i went to like 6 auto stores and none had a fuel injection pressure tester that was for an import or even parts to assemble my own (like a 5/16" t fitting and a decent guage 0-100 psi. that didn't glow in the dark and come with an APC window banner)

anyways, i went ahead and replaced my "fuel pump resistor relay" which the haynes manual calls a "main fuel pump relay" and pulled all my old auto trans relays and plugged up/disconnected everything else auto trans related.

doing all this seemed to help at first, but i went for a drive and all the symptoms came back and when i got back to the house my fuel pump was still getting the same poor voltage readings

 

i tried to edit but can't anymore... anyways i think i was measuring the wrong pins on the fuel pump... i checked the wiring diagram and between the blue and solid black i get 12 volts constant

 

The 88 NA does not even have one, and even if it did it could not cause these symptoms.

I don't know what you replaced, but it wasn't the resistor/relay because you don't have one. I can't find anything in the Haynes about a "main fuel pump relay" (what page?). The only relay in the S4 NA fuel pump system is called the circuit opening relay and is under the dash.

What are the fuel pump voltage readings? And where are you measuring them from?

Have you checked out the igntion leads? I know from experience a faulty lead can cause missing under load.

 

Could clogged injectors cause this? I would think it would cause 3800 hesitation too, but i dunno.

 

I have these same problems on my 90 GTU the misfiring, it was the ignition coils were very very very dirty i scraped the oil off the inside and now it doesnt misfire but i doubts that the problem- i was just putting the input maybe you should check yours & mine was only misfiring above 4500x

 

he said he just replaced them

 

NAPA has a tester, Balkamp #BK 7001089 for 57.99 that works well. It has all the fittings you need to deadhead it to check the pump pressure, or put it in-line to check the regulated pressures. I got one last week, and they were able to order it, and get it in the store in less than 2 hours.

http://www.napaonline.com/cgi-bin/nc...&usrcommgrpid=

 

thanks all... sorry this post is getting so long

well i just basically replaced every relay that the haynes manual said was fuel related when i remembered only earlier s4's had the resistor pack... didn't help though

the fuel pump is getting 12 volts between the blue and black wires

today i cleaned up several grounds (sanded, checked resistance, bolted, then sealed with RTV) like the trans to firewall and main battery, resoldered some wiring repairs in my secondary injector harnesses, did a full range check on my TPS (looked good, but i'm about to double check)

all this made a vast improvement in performance, but i still hit a wall at 7k (could this just be a ecu rev limit?) and could sometimes get it to sputter or hesitate over 5500 in first and rarely second (never in 3rd any more)

here are my plans:

-take off upper intake and clean/augment the ground with ring connector there and resolder primary harness repairs

-clean ground under air box

-spray out TPS with contact cleaner to make sure no drop-outs in resistance

-re-adjust throttle body plates

anything else i should consider?

 

ok, well let's say i'm an idiot and i've got low impedance injectors as my secondaries while my car is an 88 with high impedance injectors / no resistor pack (owner before me had done some hack job repair on the harness like twisting wires together and taping it) my primaries are series 5 high impedance cuz thats what i had available at the time of repair and that alone shouldnt make a difference right?. didn't realize until just now that the offeset on the secondary plug/injeector is in the center and not offset.

so yeah, low impedance injectors on my secondaries would cause this right?

 

Check or replace the - wire from the batt to the block. A pore ground here can cause a high RPM studder.