First post was her My 1st Post

MY 2nd Post

85 IROC - 870 ECM, stock PROM ( LB9 / A4 ). Engine is a '87 L98 350, ported heads ( found that out when I changed intake gaskets!!) ported intake, seems to have a bigger than stock cam.

Anyway, the spark knock is GONE!!!Turns out the EGR line under the plenum was melted in two!! It had sealed itself off, so it wasn't causing a vacuum leak, but the EGR wasn't working, as no vacuum was getting to it. Also fixed the oil and coolant leak from a bad intake gasket.

Cleaned the TB in and out. Cleaned IAC, replaced gasket. Cleaned fuel rail, replaced injector O-rings ( these were included with the Fel Pro upper intake gasket set ) threw in a new 180 thermostat ( it had a 160 in it ) put everything back together.

Set TPS, set minimum air, timing, etc, car still jumping around at idle....looking towards the distributor being the culprit, I check it out to make sure it was in right, and it turns out the pickup coil looked toasted, and there was some visible play in the shaft / bushings.....so I replace the distributor with a rebuilt, hell it did have 140k miles on it...

Got it back together, but turns out I dropped the dist in a tooth or two ( AT MOST ) retarded...BUT I can advance it enough to get the timing right where I want it, about 7 degrees BTDC, but that's as far as I can physically move it since the tach / bat terminal are now hitting the plenum...

Anyway, got everything set, car was idling as smooth as glass, only noticeable lope is in the exhaust....got it PURRING at @ 700 RPM in D and it seemed to run GREAT!!

First test drive...SPARK KNOCK IS GONE!!! So is the coolant and oil leak as well. But now it's backfiring sometimes, like it did earlier!!!

After it backfires, you can smell the gas from the exhaust..


Went to check fuel pressure...

Pressure goes to @ 46psi with vacuum line to AFPR unplugged on fuel pump prime. Cut key off, presure QUICKLY drops to @ 25-30 psi, but HOLDS there??!?!

Plugged vacuum line back up, cranked it up, pressure drops some to about 40 psi ( like it's supposed to ) and holds steady when revving.

At this point, this is what has been replaced:


- Plugs
- Plug wires ( lifetime from Autozone, I'm going headers soon and didn't want to have to buy 2 cut-to-fit sets )
- Dist cap and rotor
- Distributor ( bushings and pickup coil were toast...this helped with idle ALOT )
- Fuel pump relay ( it was coming apart..literally )
- Knock sensor for '87 TPI 5.7
- Intake gasket ( fixed oil and coolant leaks )
- 180 thermostat
- Wells SU-145 MAF, I got it NEW for cheap, and the one on there looked like the original Bosch unit


I'm not just throwing parts at this thing. Most all the parts would have been replaced anyway. The dist was needed.....and the MAF means I'll have spare that works....

ALSO...and I can't remember this happening BEFORE the intake gasket install...the car sometimes takes some cranking to start.. Not every time, and cold or hot start doesn't really seem to matter...holding the pedal down a bit, and it starts right up.

At this point I'm leaning towards the injectors being dirty,as they did look pretty cruddy when I had them out, and I cleaned them as best I could still attached to the fuel rail. I'm going to run some Seafoam through the tank and the TB tomorrow and see what happens.

Also, I'm going to turn the engine over to TDC #1, yank the distributor and make sure it's dead on so I can have more timing adjustment...it only takes a few minutes, and I want to take the cap off and ohm the coil out anyway ( only part of the ignition not new ).

Weird thing is this...before I went and picked up another fuel pressure gauge today ( mine broke ) I tried backing off the homemade AFPR ( it was on the car when I got it, and I pulled it apart and everything appeared fine ) but I did back it off a good number of turns...the car ran like CRAP......and please NOTE, the backfiring happens under load or NO load when revving in P...ONLY happens when you quickly rev it, you can smoothly accelerate all the way to 5500 RPM and it pulls like a horse, no problems! So I turned the adjustment back in ( more pressure ) about halfway back to where it was to begin with ( all the way in, but the bolt that was used is not that long ) and when to pick up the fuel pressure gauge......

Car ran like a RAPED APE!! No backfire, no misses, nothing..nailed it on the Interstate on ramp in D, it downshifted to 2nd, barked the tires and planted me in the seat...it pulled hard, until I realized the 85 MPH speedo had been buried for some time!! Picked up the gauge anyway, drove it back home, same thing, ran GREAT!!

Put the fuel pressure gauge on to check it, NO pressure changes, just connected the gauge, and while revving it in P, it hesitated and backfired?!?! Smoothly rev it all the way to 5500 RPM, it's fine!!!

Can a flaky TPS cause weird things like this? The TPS read okay via WINALDL, .6v at idle, 4.3v or so WOT, but as slow as the '870 ECM is updating the sensors, it's hard to tell if there's a drop anywhere......maybe a sticking spot or something?

Anyway to test the IAC as well? I'm not buying anymore parts until they've been tested.........seen too many good parts get replaced for this reason...

Any help or tips, greatly appreciated

Thanks
Chris
85 IROC

 

You say the cam sounds different than stock. May not have been dialed in at the right angle. Try reducing the timing a few degrees and see if that helps.

 

i thought the 85 had a different MAF system. wasn't it a digital MAF system. The Wells SU-145 is a analog MAF. that might or might not cause a problem? as for it backfiring...... seems like a lean condition. check to make sure all the wires are wired right. i did that before and it backfired through the intake. there might be a vacuum leak somewhere. check/replace tps/cts/o2 sensors. wouldn't hurt since the car is 17years old .