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84 w/CF won't start

vigman

Motor head!!!!
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Runnin Rich

Do you smell fuel? The TPS tells the ECM how far the throttle plates are open
This control's the Air fuel ratio...... you NEED to check this.


Vig!

Any Check engine light????????
 
Joined
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Messages
160
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Matthews, NC USA
Corvette
1984 Coupe
TPS

Vigman,

When I finally got it started the check engine light went out.

Will not start unless I have the throttle partly open.

Set the TPS to .525v, ign. on no throttle.

When I let off the gas it dies immediately.

This is really getting frustrating.

Help.

Ken
 

vigman

Motor head!!!!
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Location
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88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
So here's the deal

1) Take the IAC motors out and CLEAN EM.

Notice carefully the slot on the top of the TBI where you can see the pintle ( tip ) of the IAC motor from the top of the TBI clean that area REAL GOOD... DO NOT USE CARB CLEANER!!!!!!

DO NOT LET CLEANER RUN DOWN THE SHAFT OF THE IAC MOTORS... put em back in have somebody.. start the car the shut it off after it lights ( 10 seconds )

Then re start

You should see the IAC MOTORS PULL BACK AND ADJ... if they do not... you got a BAD one or BOTH... or no power to em.

Will dig more for simple tests....

Do not give up!!!!! almost there!!!!

Where is your timing set.. and how did you do it?

Vig!
 

vigman

Motor head!!!!
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Location
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88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
IAC test.....

Now note... there were 3 different style tips ( pintles ) for the IAC valve.... are these FACTORY IAC's?

TEST #1

Create a VAC leak..... remove a small vac line or 2... if you can keep the car running at partial throttle it would make sence IF the IAC motors are NOT moving to let more air in the manifold.. do it another way..... try this test first. ( DE GUNK the throttle air passages in the TBI .. do not use carb cleaner!!!!)

Test #2 ( creative test )

When you have the IAC's out find a plug to stuff in the hole that the pintles were in ( cork or rubber stopper ) make SURE that they will not get SUCKED IN!

Light the engine...( 10 sec ) shut it down.. electrically connect... but do not install the IAC's.
See if they MOVE... if not BAD DOGS!

Test #3
This assumes that BOTH the INJECTORS ARE SQUIRTIN.....

If it's fuel and not air... spray a gas down the hole ( Have an extinguisher on hand )

If the car will run.. with more fuel.... then you have a clogged injector feed.

There is a filter around the body of the Injector ( Wire mesh screen )

Since this intake has been sitting for a while... it's safe to assume that it's gunky.

So... short of that..you will need some more test equipment....

HEY WAIT... what's the fuel pressure?

Your using the orig ELECTRIC pump in the tank....right?

I assume the spray pattern from the injectors is nice @ 1500 rpm, not just a semi controlled dribble...?

Need more lookin around.....

Oh.. didyou dis assemble the TBI setup in any way... or did the previous owner????

Vig!
 

vigman

Motor head!!!!
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88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Fuel Pressure

9-13 PSI

FYI

Vig!
 

Twin_Turbo

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1982 Twin Turbocharged Red/Black
The TPS is the Throttle Position Sensor (or Sender). It sends a voltage signal to the ECM (from 0,5V at closed throttle to around 5 for full throttle) so that it can calculate (in combination w/ MAP value) what the load and therefore fuel demand (and timing) for the engine will be (if you're accelerating and such)

The IAC's are almost never the culprit and they hardly ever go bad. Clean them but never pull or press or twist the pintles.

Some books tell you can reset them by pressing the pintle in but you CAN'T! If you ground the ALDL test pinout you should see the IAC's cycle.

The IAC's will be reset when you drive above 35mph (in closed loop!).

If you have black exh. residue you'r running way too rich. Did you balance the TB's? It might actually be so rich that you're fouling the plugs immediately.

Marck
 

vigman

Motor head!!!!
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88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
I have to disagree on IAC

There's been a low failure rate...but some have failed from HEAT here in CA

#1 problem... carbon build on shaft.
#2 Heat failure ( bad coil..or connection )
#3 Missing gasket/ not tight...leaking air
#4 Mis adjustment ( Aftermarket ) pintle is adjustible

Vig!
 

Twin_Turbo

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Missing gasket and misadjustment don't fall into the failure category!. that's plain stupidity if you ask me ;)

Carbon buildup, I don't count that as a failure either. TB's tend to collect carbon as well, do you count that as a failure too? Carbon removal is considered normal maintainance here.

Also, check if you have the CORRECT IAC's. There are different pintle shapes for sticks & automatics.
 
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Messages
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Location
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1984 Coupe
carbon on the plugs.

The throttle bodies were disassembled after I got them and cleaned thouroughly.

IACs did have carbon build up but were cleaned, as well as the seat in the TB.

Pulled number one plug tonight and found that it had a coating of carbon about 1/32" thick. I'm assuming that a number of plugs are carbon fouled. It runs like it anyway.

The fact that the engine won't start with out the throttle being depressed half way is puzzling. What would cause that?

The spray coming out of the injectors seem to be forming a fairly uniform cone.

If I had a massive vacuume leak, wouldn't that tend to lean the mixure out?

Could poor spark be a culprit too?

This weekend I'll remove and clean all the plugs, measure the fuel pressure and try to determine if the IACs are moving.

No, TBs have not been balanced. What effect would that have if they aren't?

Thanks for the help,

Ken
 

Twin_Turbo

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If you start the car w/ the pedal depressed more than 1/2 it'll go into clear flood mode. If you start it w/ no throttle it won't start.. w/ full throttle..will it then start?

Seems to me you start it and by depressing the pedal 1/2 way you go in & out of clear flood and therefore fuel delivery is severely reduced.

You have an extremely rich condition. There could be several reasons for that:

*TPS not set properly. Will trigger Code
*CTS is bad or has a poor (or no) connection. Check the connector. Measure resistance over the CTS. Then pull the engine harness apart (at the firewall) containing a yellow & 2 black wires. 1 black wire will be located next to the yellow one in the connector. This is NOT the correct one. Measure the resistance over the other black wire & the yellow one. If it's not the same (higher) as the previous reading or if it's infinite you've got your problem right there. Will probably not trigger a code.
*MAP. Will trigger code.
It can't be the O2 sensor because it's still in open loop, O2 isn't used for altering A/F ratio, just monitored for voltage (if it has warmed up)

These engines live and die (especially idle & throttle response) w/ balancing the 2 TB's. However, to do it you'll 1st need to get it running. You can do it byn eye. Remove the plugs onboth TB's (plugging the idle stop screws) & break the weld on the synchro screw, Turn the synchro screw and note what plate opens and wich one closes (if the other one doesn't close it's hanging on the stop screw). Then turn the other way untill it's in dead center (the synchro screw isn't opening one throttle plate relative to the other) At this point there is the least (or no) resistance in sideplay on the connecting rod between the 2 TB's. After this back off both idle stop screws. Both plates should close completely. Then using both stop screws open both plates only a bit (I stink at measurements in inches, we use metric system, but the opening has to be aroun the size of a hair) If the car then starts it's most likely die. If so open both stop screws until it idles at a neat rpm (somewhere areound 700). Now you have a rough setting. A fine tune between the 2 TB's is done relative to each other w/ the synchro screw & using a water manometer.

http://www.crossfire.webhop.net has a tech raticle on how to do this (read it and try to understand how the linkage actually works, the adjustment can be done w/ both TB's as a starting point. The result will be the same)

Marck
 

vigman

Motor head!!!!
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Location
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88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
IAC'S

Twinnie... the only FAILURE mode is the COIL opening up ( and I have had 2 of those ).

And the carbon usually generates another failure by somebody spraying carb cleaner down the shaft and rinsing all the goo into the gear mechinism and seizing it.

Your correct on the other's being maint. issues

However... that must ALL be taken into consideration... just trying to give food for thought out here, not BAD or MIS information.

The Sync of the TB's is Critical.

The Haynes manual has a good step by step syncro procedure.

If the side cap plugs on the throttle bodies have not been removed, you can leave that adjustment for last... just get the linkage to open a bit and see if the car will hold an idle.

The object of the game is so the two open at the same rate and 1 is not leading or lagging.... check at Wide open throttle they should open @ exactly the same time.

Another way to do it is treat the TB's like motorcycle carbs.... get two vac gauges
( 20.00 each) and measure the vac at the throttle plates and adj so they both pull the same vac. do this slowly.. the IAC's will be trying to work.

And if your plugs are SOOTY...your running rich.

Pull a plug wire off the cap and watch the spark should be a nice fat blue/white one, bout 1/2 inch jump... wear gloves when doing this ZAP!

So read & tweak away

Vig!
 

Twin_Turbo

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The synchro procedure in the haynes isn't even correct. The funniest part is where they damage the TB's by drilling holes in them to remove the plugs. You can remove the plug also by boring a tiny hole in the plug itself and then using a small braddle or screwdriver to pop it out.

You must cycle the IAC's into a fully closed position and then unplug them. You can also block the kidney shaped holes w/ duct tape or something like that. Then use a water manometer on the center port of eah TB.

vigman, what do you mean w/ like motorcycles? by using unisyns? That won't work :)

Marck
 

vigman

Motor head!!!!
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Location
Valencia, CA,USA
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88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Unisys... No........ don't think so

"Another way to do it is treat the TB's like motorcycle carbs....

get two vac gauges
( what part is unclear about this.. two regular vacuum meters)

( 20.00 each) and measure the vac at the throttle plates and adj so they both pull the same vac. do this slowly.. the IAC's will be trying to work."


This procedure ( in the Haynes manual) provided accepable results, not perfect. ( the car had 134K on the clock.. and things were OLD) . I drove my 84 for 2 years and it idled smoothly @ 600 to (700 RPM Ac on) till I traded it for my 88 ( to a CO WORKER ). The car ( 84 ) still runs fine and I had seen it every M-F till last week, it was traded in on a Surbaban.

The point is... there are MANY ways do do things.. some better than others however I think the idea here is, Ken wants his baby RUNNING now and will deal with the finer point's later.

Vig!
 

Twin_Turbo

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How will you measure vac at the throttle plates? By using the center vac. port (wich does exactly that, there's small slit in the bore) The vac gauge will have to be pretty precise. It has to measure in "of water not "mercury. The adjustment is pretty precise. So you could use 2 water manometers.

I'm not trying to be annoying at all.

The haynes manifold will not get acceptable result. Idle may be nice but you'd be surprised by the difference in throttle response and power that a good synchro will do. I've worked on a lot of CFI cars and they all were out of synch.

Marck
 

vigman

Motor head!!!!
Joined
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Location
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88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Arrgh!

Ok I agree the manometers are more accurate then std Vac gauges.. but we are takling about an 18 year old vehicle not a nuclear reactor.

I surrender.....

Vig!
 

Twin_Turbo

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I swear.. that's why most of them run like crap! I suspect a lot of them are not synched but only adjusted to run a certain idle rpm.

I have done 4 crossfires here in the Netherlands last year and they were all like that.

:)

Marck
 
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1984 Coupe
CF will Start now

Vigman & Twinnie,

Time for an update.

I went out my local autoparts store and bought an ignition module, hiperformance coil, and 8 new R45ts plugs.

When I took out plugs 1,3,5,7 , they had heavy carbon deposits on them. (This was also the side that was dumping all the carbon out the tailpipe) 2,4,6,8 had carbon deposits, but not as bad as the other bank.

When I started the engine, I really noticed a difference. It now idles and runs alot smoother. Not perfect yet but alot closer than it was.

I believe both of the IACs are not working. While warming up the engine, there was a small back fire and the pressure blew off three vacuume port plugs. Instead of running rougher, it increased RPM from 800 rpm to 1400 and seem sound a little healthier. This engine is definitly starving for air.

Does this symptom sound like IACs to you?

I'll look back throught the post to see how they are tested.

Ken
 

vigman

Motor head!!!!
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Messages
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Location
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Yes

and YES!

( But that's just my opinion )


Vig!
 

vigman

Motor head!!!!
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Messages
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Location
Valencia, CA,USA
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88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
AND

You could look down the TB holes for the IAC and my capping & uncapping a Vac line ( causing the engine to HUNT... you should see em move ( very slightly ).


The OTHER trick.. is fire the engine off and shut it down before 10 sec. restart the idle should climb to 1100 and work it's way back down IF the IAC's are moving.

IAC's pull back to lean the mix out and close to richen it.

Vig!
 
Joined
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Messages
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Location
Matthews, NC USA
Corvette
1984 Coupe
IACs

Set the timing last night to 6 bdc and it really slowed the engine down. It's now idling between 400 - 500 rpm. How does the RPM increase?

Couldn't find the wire to the dist. that service manual refers to, so no wire was disconnected.

The ECM can't be conpensating at this point since the idle is so low.

Also, it backfired twice last night when I tried to give it gas.

What could cause this?

Coil, Dist. Cap, rotor, ignition module, plugs, plug wires all new.

If the ECM was bad, would the engine run at all?

Checked the IACs last night. Uncapped center vacuume port on drivers side TB and did see a slight bit of movement in the IAC.
Tried the same with the passenger side and didn't see any movement. Anyway, I ordered two IACs yesterday.

What else should I check?

Ken
 

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