poor running 84

[scooter18155]

the bad about going to carb is that ya loose mpg for one. 2ndly ya havta be carefull which intake ya use as well as air cleaner carb and so on not all of the intake and carb combos and such will clear the c4 hood. also the value of your corvette goes down. it seems noone wants a corvette that has a carb unless it came with one from the factory. im not saying theres anything wrong with a carb or noone will buy one with a carb but your going to see people look see the carb and run if ya was looking to sell it. dont necessarily give up on the crossfire it is kinda quirky and has some limitations. but it still is a good system and once ya get it running right crossfires can be verry dependable. i still have the crossfire on mine and it shocks me how well this system does. seems like everywheres i look crossfire gets put down so in the begining i was like ugh i gotta get rid of this junk. but once i started driving it and doing some simple easy modifications it opens right up and gives ya a kick in the ass. its like wow this dont seem so bad after all. now im starting to come around to the idea of getting a nice motor and keeping the crossfire setup weather its a stock intake or x-ram.

 

[geekinavette]

Pete...you CAN have backfiring through intake with a leaking EGR! (ask me how I know... :L ). It wasn't nearly as "violent" as say a stuck intake valve...but it DID backfire due to an EGR leak.


Will the thing idle? Check how much vacuum you're pulling at idle... (I'm curious!)

Bill

 

[chevyagain]

didnt forget you guys, will be pulling off plenum tomorrow, sunday,
after i get it all back together with all new gaskets and everything cleaned up, ill balance throttle bodies and see what happens, after all this
if it still does the same thing, then i quit

 

[chevyagain]

okay, replaced plenum gasket and throttle body gaskets, reset timing again
lots of gas in plenum base. started engine, still the same if not worse than before. seems to be loading up on gas, this seems to be my only problem.
plugs wet. where do i go from here. seems to idle better when it does run
way too rich. can smell it in exhaust fumes, loads up and dies

 

[geekinavette]

Most common causes of a rich condition are 02 sensor (which you've already replaced), faulty CTS (ECM "thinking" the engine never warms up), or an exhaust leak between engine and 02 sensor.

Look at your CTS and see if it is a one wire or two wire unit. If it is one wire...REPLACE IT.

Bill

 

[black_81_vette]

If its running that poorly shouldent the check engine light be on? I would think it would be if its dumping enough fuel to foul plugs.I would say a CTS would be the primary cause but I would scan the ecm and check codes and perimiters.Even a bad fuel pressure regulator will cause a way too rich condition.

 

[geekinavette]

Not if it doesn't ever go closed-loop.

 

[chevyagain]

CTS looks new, two wire--------john where do i go from here

 

[chevyagain]

there is a black relay box to the left of the map sensor on the firewall
what does this control also can i get a replacement-----john

 

[nelson84]

My 84 did the same thing, it ran at about 2200 rpm. I changed the MAP sensor and still the same. Then I changed the coolant temperature sensor on the front of the manifold and now runs great and idles at 600 to 700 rpm. Your ecm is getting a signal from the temperature sensor and it is telling the engine to put more fuel to it because the temp sensor is saying it is -40 degrees outside and needs the extra fuel to keep running but it is just flooding the engine during normal temperatures.

CHANGE COOLANT SENSOR IT SHOULD COST YOU ABOUT $40 AND 10 MINUTES OF YOUR TIME.

I hope it workshnoes.

 

[chevyagain]

coolant sesor was checked looks to be new, but i guess looks dont count
ive just about had it now, dont know what else to do. take a look at your
distributor, is # 1 wire next to the square terminal lead just to the left
or one more over------------thanks for reply

 

[wishuwerehere82]

Wire positions are marked on the ring that holds down the boots on top of the distributor. Unless Bubba removed it already.
As viewed from standing by the driver's side fender, Wire #1 will be the first wire to the left above the connectors for batt, tach.

 

[chevyagain]

thanks 82, yep, bubba screwed up again, ill get it sooner or later
thanks-----------john

can i disconnect temp sensor, or will it still run rich

 

[MoeJr]

Don't give up on the Cross Fire. Mine runs like a charm. Once you get it set it runs very well. If you were up this way I would have sent you to my friends who does all the work on mine. He is great with the Cross Fire Injection.

Once you have the issues taken care of and the TB's Balanced you'll be happy.

 

[chevyagain]

thanks for the support Moe, i dont know if that day will come, i never
heard of so many different parts that can contribute to poor running
dont know if you followed my posts but ive changed, map sensor, 02
sensor, cap, rotor, coil, ignition module, knock sensor, egr valve,
plenum gasket, plugs, wires, timed @ 6 btdc. now it will run for 12-15
seconds and die. seemed to get rid of my backfiring though.
i live in virginia its hard to find someone here who knows crossfire
im in a real rural area. just seems im floodin out, as far as the coolant sensor, if i change that, it will probably be the same. my next door
neighbor is from NH. DONT KNOW WHAT TOWN THOUGH
anymore input welcome-----------------john

 

[wishuwerehere82]

Now that you have changed the gaskets, it's time to balance the TB's. Of course it has to be running first.
I assume that when you say it's running rich, that you smell a TON of raw gas out the tailpipes and probably have some black smoke too.

Have you checked the TPS voltage? At idle it should be .525V with the ignition on between the black wire and blue wire on the connector. If it is higher than that, it will be running very rich. To adjust it, you unscrew the Torx screws that hold it to the TB and rotate the the TPS until you get the .525V on your Voltmeter.

At some point, you will also want to check out your IAC motors on the TB's for function. You can unplug the connectors, unscrew them from the the TB's and plug them back in to the harness and watch what they do. If the shafts extend and retract smoothly, they are working. If they just twitch and don't extend out, then they are bad. Once again, refer to the link for pictures of this part.
http://www.corvettefever.com/techarticles/4688_chevrolet_corvette_efi_system_tuning/

 

[chevyagain]

heres where im at, engine will run for approx 10 seconds and die
if i turn distributor countercloickwise ill get more run time, cannot turn it
any further counterclockwise wires stretched, is this out 180 deg.
or what. turned engine by hand once to TDC pointed to # 6
tuned around again pointed to# 1 ----2 turns of crank---1 to dist

removed iac from rear throttle body, replaced plug. turned ignition on, no movement
whatsoever, buzzing noise only. i only replaced the front throtlle body one
any input
removed front new iac, re-pluged, turned on ignition, no movement from this one either

 

[wishuwerehere82]

OK,
The changes that were made to the manifold gaskets have affected a change.
The change is that instead of running at high idle it now stumbles and dies out from a rich mixture. So it means you have fixed a large air leak in the manifold.

I would speculate that the previous owner has changed something (probably the TPS setting) to compensate for the air leak, just to keep it running.

The fact that the IAC motors are not moving is probably not too critical now, since they will actuate after the engine is running and gets some feedback from the ECM as far as the engine RPM and then attempts to change it to idle.

So now I think is a good time to measure your TPS voltage with the throttle plates closed and see if the voltage is set for idle. If you measure between the blue wire and black wire ( bottom and middle wires on the TPS connector) with the ignition on, but engine not started. It should be set for 0.525V with the throttle closed in the idle position. If it's higher than that, you can loosen the two torx screws that hold it to the TB, and rotate the TPS vensor until it reads 0.525V. Then open the throttle wide open, and the voltage should go up to between 4.5V - 5.0V.
That should allow you to start and run the engine long enough to get the timing reset to 6 dgrees BTDC with the advance wire disconnected.
Then turn it off and reconnect the advance wire and see if it will come down to a reasonable idle.

Sound like a plan?

 

[chevyagain]

thanks again--------keep ya posted

im readin 6.0 milli volts thats in the plud disconnected

 

[geekinavette]

heres where im at, engine will run for approx 10 seconds and die
if i turn distributor countercloickwise ill get more run time, cannot turn it
any further counterclockwise wires stretched, is this out 180 deg.
or what. turned engine by hand once to TDC pointed to # 6
tuned around again pointed to# 1 ----2 turns of crank---1 to dist

removed iac from rear throttle body, replaced plug. turned ignition on, no movement
whatsoever, buzzing noise only. i only replaced the front throtlle body one
any input
removed front new iac, re-pluged, turned on ignition, no movement from this one either

Are you absolutely SURE you were at TDC of compression, and not exhaust? I usually do that by removing #1 spark plug, holding my finger over the plug hole in the head while turning the engine by hand and feel for the air coming out...then I know it's on the way up to TDC of compresson and not exhaust.

If there's any question at all...just do it over. Not that it really matters...but #1 at the dist cap usually points kinda between the center of the engine and the EGR valve.

Also as I recall...I think you can put the ECM in diag mode (connecting pins A and B of the ALDL terminal) and "home" the IAC valves, meaning they would be fully closed...taking the IAC valves out of the picture. Pete do you recall if that's how to do that? It's been a while...

Also, the IACs won't operate "normally" again until the car is brought up to 35MPH or so (I think it's 35...).