Gibson Smith

I have an 87 13b non turbo GXL. It wasn't making full rpm from the time I bought it. Would only rev to about 4400 before it would start to become sluggish and couldn't get to 5000 no matter what. After talking to a friend he suggested fuel filter and injector cleaner. Did both no change. Then he suggested the Cat may be clogged. I loosened the exhaust below the header and the car ran like a champ. Full RPM in nuetral in the shop. But... RacingBeat was back ordered on new exhaust systems and I though I wanted a full RB exhaust. So.....I decided to rod out the Cat I had and use it till I could get the system I wanted. Long story short I did that put it all back together with all the honeycomb metal catalyst knock out of it. It ran Great! For about 3 miles, then the engine would barely stay running. I limped it home and have been trying to figure out what to do ever since. I replaced the Cat with a new custom MagnaFlow Cat and replaced the spark plugs and plug wires hoping the '"new back pressure" and clean plugs would help get the computer back to its happy place, but that failed. It is running incredibly rich grey smoke from the exhaust and it sputters. Not sure where to turn now, or if any of the above things are related. Any ideas on what I might have done and what the fix might be. I'd appreciate any helpful feedback. Obviously I now know my master plan to fix the Cat was a bad one. Just hoping there's something I'm overlooking.

diabolical1

iTrader: (3)

welcome to the board.

if you don't have a copy of the FSM, then you can get a copy here: Foxed.ca

i have a few thoughts. first, since you said you changed the fuel filter, i will assume you did the one outside the tank. i think you should take a look inside the tank as well. there is "filter" in there at the pump as well. start there. the filter/sock could possibly cause the crappy idle, but i can't think of how it would cause smoking.

the other thoughts i had are to check to make sure your secondaries are opening consistently. make sure the ground is clean and solid. i also thought maybe your auxiliary ports are not opening, so you should check them as well - particularly since you did some work in that general area of your exhaust system! these were my main ideas, but neither of them would cause the idle and smoking you described after the one "good" run you described. sadly, for that, i would say you should do a compression test, too.

diabolical1

iTrader: (3)

actually, i just thought of another thing you can check: the TPS.

DR_Knight

iTrader: (23)

Basically should go back to the basics, unless you already have and didn’t tell us.


compression, check spark on both coils, new spark plugs. Ecu water temperature sensor, o2 sensor, tps setting.

including boost pressure sensor and maf reading. Yup literally everything since were all in the dark here.

Akagis_white_comet

iTrader: (4)

This might sound dumb, but practically all driveability depends on the Air Flow Meter for air volume calculation, in order to fire the injectors the proper amount. On a healthy car, if the AFM is unplugged, lack of signal will make the engine stall. Also, the signal is ground-referenced, meaning an iffy ground will skew the signal, making the car act funny as OP has encountered. I would surmise that gutting the cat changed the backpressure amount, affecting the Auxiliary Ports (either opening or closing them, can't recall offhand, check the manual) and partially correcting the air flow miscalculation, hence it running properly for a few miles. Then, after those few miles, the ECU goes "Dude, this ain't right" and would barely run.

Aaron Cake explains the ins and outs of proper grounding here:
https://www.aaroncake.net/RX-7/grounding.htm

It certainly could be the Air Flow Meter acting up, based on the stalling behavior, but I would service the entire ground system first and re-test. Ground locations are in the Manual, but I'm fairly sure the AFM Ground is underneath the Upper Intake Manifold, which is also shared with the ECU. Read the article, it spells it out why it goes goofy and how to correct it.

EDIT. Almost everything related to engine control is grounded here. "If this ground is poor, then all manner of weirdness can result including the infamous 3800 RPM hesitation.". Seems like the right place to start.

Gibson Smith

Thanks to each of you for responding. Sorry I didn’t reply sooner I was having trouble logging back into this account. Turned out to be mass airflow. The gate was stuck for open causing the computer to dump fuel even at idle. I was able to tap the gate with my finger and it shut, now the car runs great. But thanks to everyone’s input I was able to test ignition coils, compression, oxygen sensors and ECM. All are in perfect working order! Thanks for the help I really appreciate it!

diabolical1

iTrader: (3)

congratulations on getting this sorted out.

also, kudos to Akagi's White Comet for hitting the nail on the head.