my '85 V6 is stumbling intermittently, usually just after start up, or when cold, I was thinking plugs and wires, so I replaced the plugs (champion platinum) and wires (bosch), no change, I also replaced the cap and rotor, and the fuel filter, any ideas?

 

NEVER, ever, EVER use Champion plugs in anything other than either a Crapler product or a lawn mower! Okay, enough ranting...

Check the resistance on the fuel injectors... Should be 12.6 ohms a piece, within a full ohm between the lowest and highest. Also check the resistance of the coolant temp sensor and the air temp sensor in the air box.

 

cool deal, I was thinking injectors, hoping something cheaper though I'll check the IAT and CTS tomorrow. BTW, the engine is not throwing any codes.

Any suggestions on where to but injectors and what size?

Thanks-

Eric

 

South Bay fuel injectors or fuelinjectorconnection.com, $160 a set, roughly. 15.4#/hr rating OR 14.7#/hr, the 2.8 uses both. Probably be better to get a set for a 3.1 (15.4#) as they don't have the pintle caps that are prone to fouling.

 

I'll need to re-tune if my car has 14.7's and I go to 15.4's correct?

 

Nope. The changeover year for the 2 injector styles was 87... We had a choice of either injector, and the chips were the same. I got shafted and got the crappy ones.

 

is there any way to ohm out the injectors without removing the upper intake?

 

Air filter, check timing, seafoam the engine, personally I like E3 plugs. Check the throttle body for carbon deposits around the butterfly plate. If none of those are the problem its probably MAF sensor, IAC, TPS or o2 sensor. And it won't necessarily throw a code either, prime example, my mom's car kept stalling at idle, I did a tuneup on it(plugs, seafoam, fuel filter, air filter) and told her if it kept stalling it was probably her IAC, TPS or o2 sensor. Well after I finished all that stuff her SES light comes on....I told her to just take it to advanced auto or w/e and have them help her pull the code, but she took it to a shop instead, guess what, bad o2 sensor.....and the car doesn't stall anymore.

 

o2 and airfilter are both brand new, for some reason, I never thought to check the TPS, I'll check it in just a few.

 

Disconnect the 4-way connector at the front of the engine and measure the resistance between the first and third and the second and last terminals, should be about 4 ohms per set (bank of injectors). This is on the injector harness side of the connector, BTW, not the engine harness side.

 

just wondering but what did the tips of the plugs look like?

 

well, I just bought a link cable (needed one for quite a while).

I'll hook it up to the old laptop next week when it get here and see just what's going on.

 

They actually didn't look to bad,





I'm going to pull one of those champs and see how they look. the cap and rotor were shot though, they've been replaced and should be fine.


The stumble is at it's worst when under load. I backed the car onto some ramps so I can do some exhaust work in the morning, and it stumbled so bad it stalled.

 

Fuel mixture is almost dead-on. That's the color you're looking for. For that cylinder, anyways. If all of them are the same color, I'd look elsewhere for the problem (loose valves or something).

 

it's an intermittent issue (although it is happening more and more), so the plug could look good, and there still be a fueling issue.

 

it only happens at low speeds, accelerating or under heavy load, it won't do it in neutral while free revving, and is usually worst right after startup.

 

any bad vacume lines?

 

no, it's also to inconsistent for vacuum lines to be the prob.

 

Does this happen at some particular point in time, say, after you make a turn to the X direction, or when you step on the brakes, etc, or is it just completely random?

Did you check the IAT and CTS yet? What does the signal coming out of the MAP look like at idle (green wire to black wire, voltage reading here)? Have you replaced the ign coil recently?

 

it mostly happens shortly after startup, hot or cold, and mostly when the engine is under load, it's non directional,

something else I should mention, when it happens, it only happens for 4-5 seconds, and then it's over, and it may not happen again all day, or it may happen again next time I touch the gas, I should be getting my ALDL cable in sometime next week, I'll do a couple of data logs and see if I can't catch it in the act.

 

I got my cable in yesterday, and I've been playing around with tunerpro RT trying to get it to datalog. I am getting data though, and I've noticed 2 things that seemed odd, one, my TPS never dropped below .88(shouldn't it be at .5 at idle?) and my o2 sensor at first startup, would give a fairly smooth and stable readout, but if I put the car in gear, and immediately go back into park the o2 will not stabilize. it will go from the top of the scale to the bottom, and very inconsistently. I've got tommorow and tuesday off, so I'm going to run a few more checks and see if I can't get this right!

 

check your EGR and Solenoid if equipped...

 

are you saying thats what's causing the stumble or the erratic o2 reading?

 

it's a possibility...

 

1. TPS needs to be reset to .55V or thereabouts as yours is WAY high.
2. O2S won't stabilize readings until the engine temp is about 160* or the exhaust reaches 600* as it will switch states too slowly (which is why the ECM ignores it until closed loop as it won't read properly). You may also need a new sensor.

 

I got the TPS down to .57 volts, o2 is still bouncing around, even once the engine is up to temp (180-200*) everywhere from 5mv -700 mv. the sensor has maybe 2500 miles on it.

 

Remove the MAF sensor and take a look at the film inside. If it looks like the surface of a lake, you'll want a new one. A MAF in this condition won't throw a code a good portion of the time, but it may rarely throw a code 33. Also check the coolant temp sensor's resistance as that is another thing that the ECM reads to calculate the air/fuel mix.

Also check all of the connections to the CTS, MAF, and the intake air temp sensor in the air box or can, as this could be caused by a loose connection.

Another thing, is the ECM spitting out any codes?

 

it's a map car, not maf, I'm gonna check the IAT, tomorrow, I'm still trying to get tunerpro to let me datalog, it's being a pain. anyone in Pensacola want to show me how to make it work? I'm getting readings from the CTS, and they seem accurate, loose connection sounds right, I'll have to start doing some digging, I still haven't ohmed out my injectors though, but I don't think it's an injector issue, unless one is sticking.

It's still not spitting any codes.

Thanks for the help so far.

-Eric

 

Um, unless the car has a carburetor, if it's an 85 with MFI, it has a MAF. The RWD MFI V6 had MAF control until 90, when it went back to a MAP, before it got both with OBDII.

That is, assuming we're talking about an 85 (as the topic title says).

 

The V6 in question is in my "stubby firebird"

 

I'm having similar problems w/ my 85 Firebird 2.8. Stalled one day on the way to work, and would not restart. Found no fuel pressure and replaced pump and sender and pulsator. Lost spark and found dead coil, replaced it. Checked timing components and found them loose but in time, replaced anyway. Pulled intake to check for leaks, none found. No external leaks found. My compression shows good and even on all cyl's.
My problem is I have about 15-16" of vacuum on start up, as it warms it slowly drops to around 10". Use of backpressure gauge shows no exh restriction. I am out of ideas. still loads up badly and stumbles the warmer the weather is. (75 deg+) Very long cranking from 40 deg and lower.