poor running 84

[wishuwerehere82]

ok with new plenum gasket, and all the parts i replaced, double and
triple checked all; vaccum lines, where didnt i look for a vaccum leak

EGR control valve
A.I.R. pump control valve
Evap. purge cannister
Brake booster
Headlight vaccuum lines

All can be plugged, one at a time to isolate a leak.

 

[Buccaneer]

EGR control valve
A.I.R. pump control valve
Evap. purge cannister
Brake booster
Headlight vaccuum lines

I agree with Pete, these can all be possible sources of a vacuum leak, there's a ton of places on these cas for that to happen. Check them all and those TB shafts. I can't stress that enough because they are a major player in regards to vacuum leaks especailly with high mileage and even some as low as 29k.

And yes, like I said before, FP plays a very important part on a CFI motor. You MUST know what the FP is set at now before going any further with the tweaking of the motor. In other words...from the intake manifold on down is just your average GM 350 motor. However, from the intake up is where the quirky stuff starts and it is important to get that squared away before doing other things.

I didn't know that the motor was running rich becuase you never said that before until now. That may be all tied into the FP/balance/TPS setting or other items. Just get the basics covered and squared away and everything else will start to fall into place.

One more thing...I also agree with Bill that a backfire is rather strange out of only one TB, it could also be a burnt valve(s). That can't be ruled out at this time unless you have checked for that already.

 

[xfirez51]

chevyagain,

Have you checked to make sure the Harmonic Balancer is not slipping? Its a 2 piece and they go bad with the outer ring slipping around when motor is running. You may find that you're actually 60d out of phase on timing but it'll snap back when motor is shut off. I looked for the problem for over 2 years doing exactly what you're doing.

 

[chevyagain]

whats a good way to block the iac ports, just a piece of rag or rubber grommet

 

[xfirez51]

whats a good way to block the iac ports, just a piece of rag or rubber grommet

The easy way is to short the ALDL pins as if you were going to read any codes. Then turn key on, but don't start motor. You should here the IAC motors pulsing back and forth. Unplug both of them with ignition ON. Shut off ignition, remove shunt from ALDL terminal. Now start car. IAC ports are sealed and you can start balancing TBs.
Are you sure balancer is not the problem?

 

[geekinavette]

The easy way is to short the ALDL pins as if you were going to read any codes. Then turn key on, but don't start motor. You should here the IAC motors pulsing back and forth. Unplug both of them with ignition ON. Shut off ignition, remove shunt from ALDL terminal. Now start car. IAC ports are sealed and you can start balancing TBs.
Are you sure balancer is not the problem?

That's assuming the IAC stepper motor and pintle are operating correctly. I would just plug the port with a piece of rubber trimmed to fit (make SURE it can't get sucked in!) to completely eliminate any possibility of any air at all getting by, then go from there.

Good point about the balancer ring also...just went through that myself!

Bill

 

[chevyagain]

thanks again, you guys must be dedicated, i have never seen so many
different things that make this engine run so bad. how can you check
balancer

 

[xfirez51]

That's assuming the IAC stepper motor and pintle are operating correctly. I would just plug the port with a piece of rubber trimmed to fit (make SURE it can't get sucked in!) to completely eliminate any possibility of any air at all getting by, then go from there.

Good point about the balancer ring also...just went through that myself!

Bill

Bill,

If they're not shut off at that point, its a good indicator the IACs aren't working properly and no use in balancing the TBs. In the 24years I owned my Xfire, I think I ran into a bad IAC motor maybe once. They get a bad wrap as a source of surging etc. when all they are trying to do is keep the motor running.

Chevyagain,

As for checking the balancer, I'd pull the distributor cap and crank motor till rotor is pointing to #1 cylinder. Then look at timing mark. Is it at or close to 0d BTDC? If it is, then start motor with EST connector unplugged. Check timing again with motor running. Where is timing mark? IF its not near the same spot when motor was off, then outer ring is slipping. Mine would show as 60d off because of slippage from engine rotation. Shut motor off and it would snap back.
You could also pull valve covers off and check #1 cylinder rocker position to rotor position then timing mark.

 

[chevyagain]

ok will do, im in the process of hooking up a fuel pressure gauge at present
want to make sure fuel pump is giving right pressure. i have a chevy
mechanic coming saturday who is a friend of a friend but who knows
they promise but here it doesnt mean anything. im going to work
on gauge and iac checking this P.M, if i come up with something
ill post it. otherwise ill wait till later on in the weekend after
my crossfire GURU gets here-------many thanks to all

JUMPED PINS IAC UNITS ARE WORKING TRIED TO START WITH DISCONNECT AND CLOSED NO GO

 

[Buccaneer]

The damper is another possibility and good catch, it should be checked to see if it has slipped. If it has slipped, this damper is a cure for that in the future along with other types similar. http://www.fluidampr.com/CHEVROLET.htm

Also, keep in mind that when you check the FP, if it is at or under 12psi you need to increase the pressure to 14psi and then check to ensure that it doesn't drop when rpm is increased. If you can't get the psi wanted/needed, you might as well go with the 85 vette pump which is a direct replacement and then check/adjust the FP again.

One more thing, you'll have to remove the rear TB tower to adjust the FP if the blocking plate is still installed and then remove the plate, make the adjustment and see if its what you want. If not, do the whole thing over and over until you get it right. Or you can contact me via mail/PM and I'll let you in on something else if interested.

Please post your results...I'm dying to see what is going on.

 

[geekinavette]

Bill,

If they're not shut off at that point, its a good indicator the IACs aren't working properly and no use in balancing the TBs. In the 24years I owned my Xfire, I think I ran into a bad IAC motor maybe once. They get a bad wrap as a source of surging etc. when all they are trying to do is keep the motor running.

Not giving anything a "bad rap"...just going through the process of elimination! (I've personally had three bad ones)


Bill

 

[wishuwerehere82]

So at this point, the IAC's are closed after the ALDL was jumpered and the engine won't start with the IAC's unplugged.:ugh
So it would seem that the throttle plates are closed so far that there is no air getting in to support minimum idle.
If you look at the throttle plates in the TB's, they probably are closed shut against the TB throat. You can turn the idle screw on the rear TB clockwise to open the throttle plates a little so they just start to open and try starting the engine with the IAC's still disconnected. If it starts, and the idle is too high, you can back off on the screw until the idle comes down to a reasonable speed.

 

[wishuwerehere82]

Not giving anything a "bad rap"...just going through the process of elimination! (I've personally had three bad ones)


Bill

Yeah, and both of mine have gone bad. They just twitched instead of moving in and out. So after 24 years, they will go bad from sitting or just burning out the motors.
But he has 2 new ones on and they seem to be working properly, and there is still some more problem solving to be done.

 

[chevyagain]

good news, having a GM MECHANIC HERE TOMORROW saturday knows
crossfire, a friend through a friend, im puttin an end to CHRISTINE
tomorrow her radio goes out for good, will keep you all posted
many thanks-----------------john in va.

 

[xfirez51]

Not giving anything a "bad rap"...just going through the process of elimination! (I've personally had three bad ones)


Bill

Not suggesting you are Bill. I was only trying to say that there are usually more fundamental problems that cause the surging. I've been guilty of this myself and found that I was wrong.

 

[xfirez51]

So at this point, the IAC's are closed after the ALDL was jumpered and the engine won't start with the IAC's unplugged.:ugh
So it would seem that the throttle plates are closed so far that there is no air getting in to support minimum idle.
If you look at the throttle plates in the TB's, they probably are closed shut against the TB throat. You can turn the idle screw on the rear TB clockwise to open the throttle plates a little so they just start to open and try starting the engine with the IAC's still disconnected. If it starts, and the idle is too high, you can back off on the screw until the idle comes down to a reasonable speed.

I agree on this.

 

[chevyagain]

checked fuel pump pressure today, highest 9 dropped to 6, i guess im on my way should have done this first thing. will install new pump next week and fine tune, christine has had it. will keep you all posted, as the song says
ON THE ROAD AGAIN!!!!!! JOHN

 

[geekinavette]

That'll do it!

When you replace the pump, use one for a 1985 Vette. It has been a while, but I think there's one minor wiring change you have to do...different connectors or something. Tom, pete...do you guys recall?

Bill

 

[chevyagain]

whats the difference between the 84 and 85 besides wiring

 

[geekinavette]

The 85 pump is capable of much more flow.