Running oddly...

[McKenney]

K So I have an 87 GTS coupe. It's a 7 rib hi comp with a big port head. Stock short of a K&N and muffler. Car has run amazing for over a year with little to no issues. For the past month or so I've had issues that come and go. The car will run fine and pull all the way to the rev limiter. And sometimes it'll start popping and detonating at lower rpms and refuse to climb thru. I ALWAYS run 93 octane and get fuel at the same 2 places almost all the time. Thought it was the vane flow meter acting up again as the car did a similar thing when I got it and that was the issue. Replaced it with a new one, same problem still occasionally came about. Moved on to the rest of the ignition, pulled the cap and found oil leaking into it(which explained the oil leak I couldn't find), replaced distributor(twice because the spare I had had a leaking seal too). Still same problem. Double checked timing, its at 10 degrees advanced. Replaced cap and rotor, coil, igniter, wires, plugs, checked compression(190-195 all the way across the board), still the problem is present, but not all the time. When it does it, if you turn the car off and restart it it will pull to 7500 in all 5 gears. Punch it after that and it will sputter again. So I moved to fuel system... checked injectors, replaced cold start awhile back but checked it again, all fine. Replaced fuel filter, didn't help. I even replaced all the fuses and relays to ensure that wasn't the problem. I have richened up the air flow cuz it was way out of wack from the box. But the problem persisted but isn't constant. Sometimes I can drive for hours beating on it and it runs like it always has, other times it'll run like ass the entire time it's running. I have checked for head gasket issues, no leaks to be found and compression is fine. Oil is Royal Purple and is water/coolant free. I have even replaced ALL the vacuum lines! My tvis is open all the time now but that hasn't ever affected it in the past. I have new fuel pump and strainer... I haven't installed it yet because once I do if the problems still there, I'm stuck with it. I've come down to it being either a computer issue, or the fuel pump.

[McKenney]

Timing belt is fine too! Double checked it. It's golden! I'm at my wit's end here. I've done everything I could think of 'cept for the fuel pump and the computer.

[McKenney]

I also replaced the o2 sensor awhile back. The fuel pump I replaced 6 or 7 months ago because it was going out. I have an 85 GTS parts car that had a good pump. I think the reason the restart thing helps is because it's in open loop(which would point to the computer) or because the cold start is on(which would point to the pump). Any ideas? Does anyone have a good 86 87 computer I can borrow to eliminate the ecu? I'm willing to buy it if it fixes it... And if not I have a new fuel pump.

[dr.occa]

yeah, ecu would be the next thing to test. possibly a short between ecu and tps, afm or whichever when car is jostled? to be sure it's the ecu, you'll have to run on the test ecu for a bit. double check ecu connectors that none of the pins are slipping or wires possibly on last leg. o2 sensor won't make much of a difference. afm could be going out the door. did you already test that?

[McKenney]

AFM is new(reman unit but new nonetheless). I checked the connection at the ecu and all the wires look ok and are snugly connected. The car has 193k on it though.

[Projectgofast]

Have you checked/ repaced the spark plug wires? Also take a good look at all your spark plugs I had a simular issue once it turned out to be the spark plug, it had a small crack on the insulator

[McKenney]

I've done the plugs 5 times during this ordeal and it hasn't made a difference. All gapped appropriately. I've got NGK wires on it and I ohmed them and they're all about the same resistance.

[mooreofit]

is there oil in the dizzy? also i suspect a wiring issue on the afm circuit also

[McKenney]

There was oil in the distributor. Replaced the whole unit with a new one for an MR2. Pulled the oxygen sensor out today and looked like ass so I replaced it. New fuel filter as well. I have a Walbro 255 but I'm avoiding doing the pump right now. Laziness. I have an access panel in the trunk so it ain't hard just don't wanna f-bomb with it unless I have to. Relaxing for a bit cuz I just changed my entire suspension and I'm tired. Gonna go drive it here in a bit and find out if I'm gonna be swapping the fuel pump today.

[McKenney]

So ended up doing the fuel pump. Walbro 255 now resides in the tank. Replaced the maf(vfm) again today and ran good. Got a check engine light on the way home but the only code I get to flash is 5... According to everything I could find 5 isn't a valid code... Adjusted the vfm a little richer and car pulled great. 8 minute "shakedown" session, never acted up. So I think I'm good. Any chance the lack of the distributor heatshield could cause it to break up under load after cruising at hiway speed for a while?

[dr.occa]

do you still have the top factory header heatshield? it wouldn't hurt putting a heatshield on.

[McKenney]

Header heatshield is still on. Code 5 is either oxygen sensor circuit malfunction or ecu. Got another new o2 gonna install and some new plugs cuz its breaking up more. Hopefully that fixes it. Anyone in the dfw area got a spare ecu for a kouki bluetop car?

[dr.occa]

i have my doubts that the o2 would make a noticeable difference in the car's performance. the ecu isn't all that sophisticated...it's a single wire o2. still, new parts are new parts right.

have you already rebuilt the dizzy yet?

[mooreofit]

car runs exactly the same without the o2 sensor.

if you can replicate the issue, put a timing light on all spark plugs and see if the spark is running off or dropping out. if its running off, the map sensor is commanding this or the theres a crank cam position sensor issue. if its dropping out check the coil and wiring if all is ok suspect the ignitor. if the fuel pump was the issue it would buck and surge or leave you stranded.and also i had an issue with compression and it would hold just fine under cranking during the test but as soon as i started it it would stumble at idle and misfired horribly all the way till 3500 rpms.

[dr.occa]

even though it's a high-comp it still doesn't run map unless he converted over to the jdm map and ecu. alan and i were discussing similar symptoms with cory's (jdm ae86) and he suspected the ignitor and/or coil and i did as well. the cars are old right.