williammackean

Problem:
It runs poorly most of the time. It feels like it is cutting for one revolution, then runs fine for a few moments, then cuts again. Occasionally it feels like it is running ~ half power, then it kicks in like a monster when I reach 1/2 throttle. It also drops idle & stalls when it gets like this.

No Codes.

What I know it is not:
TPS & position
IAC - new
MAF Module - New
MAF Sensor
ECM - Rebuilt
Vac Leak
AFPR - New & ~43psi
Fuel Pump - New

My thoughts:
1. Fuel Injectors. The MAF Burnoff Module (aka Fuel Injection Relay) replacement helped some. It was worse! This tells me that a bad injector could have weakened it. ?? Where can I get a noid light? I could not find that term on store websites. I'll test resistances tomorrow.
2. Ignition system. I'll run it in the dark and look for shorts. I'll also test the wires. I have all new ignition innards with less than 8k on them.

Demonic85

Sounds like your onto something there. Definitely get those checked. It should be between 12 and 16 ohms.

rick lambert

I bought an ASTRO #7898, one cool set, not only includes several noid lites, but also an IAC signal tester. I got mine at a local speed shop, but here is ASTROS # 800-221-9705 to find a dealer near you. The kit includes the following noid lights; GM TBI, GM SCPI, GM PFI, FORD TBI, GEO TBI, BOSCH PFI, IAC square 4 pin GM, IAC flat 4 pin GM. Like I said, one cool tool...easy to follow instructions, and it wasn't very expensive.

Don't know about the ohms for an 85, but the FSM for an 87 says something like above 10 ohms. What you're really looking for is for all of them to ohm within something close to +/- .5 ohms. Now ohming them will only tell you the health of the injector coils.....not wether they're leaking or not, for that you'll need to do a fuel pressure test.

Oh, and BTW, everything I've read says when you replace a MAF relay..don't just replace one, but replace both...the MAF power relay and the MAF burnoff relay.

86vettral

fuel filter possibly?

capevettes

I was thinking the same thing. I like to start simple before I make a project out of things. Sometimes when you change a fuel pump, crap can migrate and plug up a filter. Probably more complex, but worth a shot. Good luck

williammackean

I'll look it up! Thanks.

The '85 does not pave a power & burnoff relay. It has a burnoff mudule mounted under the dash by the ecm. Quite the pita.

This one is 2 yearls old to the day. That's ~ 10k miles. Might be worth doing anyhow.

To the ohm meter!

williammackean

All injectors are @ 16.5 +/- .2 in a cold condition. I have connector cleaner on them right now, so I'll wait 'til they dry to warm them. I am doubting I'll find much variation.

So, that leaves us with an injector firing fault (noid lights on the way) or an ignition problem. Might be worth replacing the pickup coil and module... Maybe get a spark tester, too.

Ideas?

Is it possible that the Hypertech Stage II chip is messing things up? This all started after headers, chip, 52mm tb, and plenum porting. It is pissible that something got goofed up when we had the ignition system and everything apart...

Muffin

You still haven't commented on checks of the timing system. Suggest those checks before you start taking things apart.

williammackean

My tuner checked the timing when it was running properly. It checked out OK. It is possible that the balancer spun a little, thus throwing off the timing.

It is now running well, again. I beat on it a bit to try to get it to fail again. No dice. (It does this. Runs perfect. Misses and runs like crap. It's a gamble every time I start it.) I am wondering if the pick up coil is slowly going out.

Thoughts?

rick lambert

Ther's a procedure to check the pickup coil in your FSM, just don't forget to wiggle the wires when you check it.

arieswebb

Try to run a wire from -neg. side of the batt. to the block or good ground point on the motor.
I have seen this a few times with the C4's
Just do a quick connect for a test if it works do a nice permanent wire up.
Hope this helps !
Bob M.
1986 4+3
1964 GTO
1983 280ZXT

williammackean

Given a few 0 - 5v box curve readouts, I have suspected a ground issue. This may explain why my stock Blows stereo system never keeps time. It's always a gamble what the time will say when I fire it up. Also, it will lose ~ 20 minutes per 8 hours non-stop driving.

Thoughts?

arieswebb

I have had the main ground point on the fire will give a bad connection on my 85 & my 86.
I would start there.
Bob M.

williammackean

Is this able to be reached from above? I'm a vehicular electronics dummy.

Also, would this explain why it runs perfect sometimes and ragged with a high idle others? Serious. There are times where this monster runs better than anything I have seen. Other times (in the same day even) it cuts off for one microsecond at cruise, and a high idle (1700-2000)

I have wondered if the high idle is caused by the fuel canister circuit staying open causing a leak with fuel vapor. No other leaks detected by high-end professional tuners.

viii

my 85 had the same problems when I bought the car a long, long time ago - the stealership eventually replaced the ecm after much time in the shop. I know that you mentioned that yours was new but it might be worth a recheck...

I did have exactly the same symptoms. cutting out, running like a beast, cutting out again, idle all over the place. fun making a left turn with an on coming semi when I never knew If I could get out my own way... good luck

arieswebb

If I recall correctly, all the grounds are on the passengers side about 1/2 way down the fire wall.
I don't have my car with me today but I can look tomorrow if no one else responds.
Bob M.