hard starting....

[jonjon]

Hi,

I have a 1988 corvette that starts right up, perfectly, every 1st cold start of the day (one click of the key and she's running!).

After i take it out for a ride, and re-start it , it cranks longer (about 5-7 seconds), then the idle sputters down until i give it some gas, then it smooths out.

Reguardless, the car runs and idles just fine while driving. I just can't get it to start right up, like it does the first start of the day.

Could this be a cold start injector "staying on" problem, or a fuel pump check valve perhaps?

Thanks.

[77CVT]

If it is one thing I have learnt from C4's is that it could be one of 100 things!  The cold start is not ecm connected so you could try disconnecting it.

FWIW, my car had the same problem.  Start immediately first up, turns out it was my earth lead - I replaced it and I have had no trouble since.

Have you reset your IAC? Idle speed?  The IAC should be 28mm (I'm pretty sure) from the base (not incl the gasket) to the end of the pintle.  Here is a tech tip on the idle speed.

How to Adjust your Early C4 TPS and Idle Speed

by Lars Grimsrud

This tech paper will discuss the procedure for correct adjustment of the Minimum Idle Speed and for adjustment of the Throttle Position Switch (TPS) on the early C4 Corvette TPI systems.  These steps apply specifically to the 1985 model year, and in general to other years.  Later model years do not have adjustable TPS’s.

General
Idle speed and off-idle throttle response on the early TPI systems is determined by correct adjustment of the minimum idle speed screw combined with a correct setting of the TPS.  I’ve seen many of these cars that have had their idle speed “corrected” by well-intentioned mechanics and owners by simply screwing the minimum idle speed screw in a few turns.  This really messes up the settings, and will not make your car perform properly.  Doing a correct setup of the TPS is one of the easiest ways to make your car feel and respond better.  To maximize the benefit of this procedure, I recommend that you first remove your Throttle Body (TB), disassemble it (it’s incredible easy – there are a total of about 5 pieces in it…), clean the TB up really good with some spray carb cleaner, and put it back together.  A nice clean TB will really put an edge on the performance improvement you will get by doing this procedure.

The Service Manual has instructions for doing these operations, but the directions are scattered through several sections of the Manual. Here is the complete, step-by-step process for doing this (not including TB rebuild).  All specs and steps are taken directly from the Manual (all 3 different sections), and this process is absolutely correct.


Tools & Equipment
You will need the following tools and equipment:

1.  A set of Torx wrenches.  You can buy a complete set in a nice, genuine plastic pouch at Sears.
2.  A good digital voltmeter that will read voltages less than 1 volt.
3.  A paper clip.
4.  A small screwdriver.


Procedure
There are two electrical components on the TB that you will be working with: The TPS and the Idle Air Control Valve (IAC).  Make sure that the connectors for these two components are easily accessible and that you can easily disconnect the IAC.

You will also be playing with the diagnostic connector under the dash.  Remove the cover (if it’s still in place).  Bend your paper clip into a “U” shape.  You will be playing with the two top right hand terminals (“A” and “B”) in the connector.

•   First step is to set the minimum idle speed.  If nobody has messed with this on your car before, the set screw will be covered by a pressed-in plug.  It’s located on the driver’s side of the TB.  Remove this plug if it’s there.
•   With the IAC connected and the ignition “OFF,” stick the paper clip into the diagnostic connector from “A” to “B.”  This grounds the diagnostic lead.
•   Turn the ignition to the “ON” position without starting the engine.  Wait 30 seconds.
•   Now, with the ignition still in the “ON” position, disconnect the IAC connector at the IAC.
•   Remove the paper clip from the diagnostic connector.
•   Start the engine and allow it to reach normal operating temperature.  The idle speed will probably be really low, and you may have to coax the engine a bit with the gas pedal to keep it running for a while.
•   If your car is an automatic, set the parking brake and put the transmission in “DRIVE.” If your car is a manual, leave it in neutral.
•   Adjust the idle speed screw to obtain 400 rpm in drive or 450 in neutral.
•   Shut off the engine and re-connect the IAC.

That’s it for idle speed.  Now on to the TPS.

There are 3 wires stacked vertically on the TPS.  You will need to be able to measure the voltage between the two top wires.  You can either buy a special harness connector that breaks these wires out (from Mid America), or gently pierce the insulation of the wires with the pointy prongs on your volt meter.  You can also stick a paper clip into each of the two top locations of the connector and clamp onto the paper clips to measure the voltage.  Whatever is easiest for you.

•   Turn the ignition to the “ON” position without starting the engine.
•   Loosen the TPS Torx adjustment screws.
•   Set your volt meter to a low scale DC volt setting that will accurately read less than 1 volt.
•   Measure the voltage between the two top TPS wires.
•   Adjust the TPS by rotating its position until you get a reading of .54 volts.
•   Tighten the Torx screws and recheck the voltage.  Re-adjust if necessary to make sure voltage is right at .54.
•   Turn the ignition “OFF.”

You are now in perfect adjustment on idle speed and TPS output.  Start the engine.  It may take a few seconds for the car to “catch on” to its new settings.

[jonjon]

Thanks,

When you say "earth lead", you mean the ground wire to the battery, correct?

How could this effect a later re-start?

BTW, my car has 52,000 miles on it.

How can i test the ground wire, and how did you know that, that was the problem?

Thanks.

[77CVT]

Maybe the heat made the continuity less???  I know because when I started it in a carpark and smoke plumed from under the bonnet because it fried the smaller backup earth wire.  Not a good feeling! ;eek

Luckily I had my socket extension with me - sit it on the -ve terminal and rest the top against the cross brace above the battery and violia, instant start.

I guess the best way to check if yours is good or bad is to jumper lead the -ve to the block when it is hot - easier starting then earth is bad but I suspect you have a more sinister problem.  ;ay

[MJ355]

had a similar problem with the 85 vet and the 91 camaro what it was when the starter gets warm and it makes the core heat up and gives u trouble starting then i would have to wait fo it to cool down  the best way to fix this problem is to put a gear reduction starter motor in

[jonjon]

I don't believe it is related to the starter, as it cranks just as fast all the time.

I also have the factory starter heat shield still on it.

[Vette Obsessed]

Guys, for what its worth 88 Corvettes have a gear reduction starter fitted as standard.

[jonjon]

I read a tech bulliten (no-photos) explaining that it can be tested by disconecting the switch, and checking it with an ohm meter. Above 200 is no good, and 20-200 with temperature less than 95-degrees is also no good as well. I guess the switch should read 200 exact.

Can anyone with a service manual verify this for me...

Thanks.

[DMCPONT]

.. you also should be aware of the COLD START SENSOR under the plenum...    Its an easy check or fix or replace the thing..
    The CSS, beside malfunctioning can also 'tar up" over time & then prohibits the quick reading of  temperature etc interfacing the info indirectly back to the ecm incorrectly - hence the engine runs like a dog.. and chokes.. often carbons up.. out of the open road it chugs along fine.
   If a  new CSS is needed they are here in oz at  a few place no doubt but straight away on the Corvette '84+ section of  www.usgmsp.com  & cost  A$111 +gst.. here taxed delivered done etc (genuine GM not copy).. or are  also available from  GM in the U.S.A if thats closer for retail US$72+freight etc.
    This is a common problem & sounds alot like the description your giving.
     This is what it looks like.. note the small square twin pin head.     Hope this simply helps you.
www.usgmsp.com

[jonjon]

Thanks,

I just checked that switch with an ohm meter, and the reading was 37.5. My local chevy dealer said, anything under 20 on a ohm meter is no good. I just checked a brand new one out of the box, and it read 37.2. That seems close enough to be OK.

The chevy dealership thinks that i have leaking injectors.

[77CVT]

If you got leaking injectors you could end up having my woes at Melbourne - the extra fuel on startup can hammer the rod bearings!

[2 short]

i realise this is an old topic but because i have the same problem i was wondering what the fix was?
only difference is mine is an 85 model.

[TIPPA]

Sounds like all knowledgeable advice given so my caveman possibility may be way off but here goes... could it be a vapour lock in the fuel line or rail? Maybe the engine heat causes a fuel vapour lock and the pressure pump hasn't enough time to build fuel pressure before you crank it...
Just a thought but then i am used to carbies...

[daniel42au]

does it pull a engine code? ie "Service Engine Soon" on the center display console?
There is a water temp sensor down under the throttle body which if it play up makes starting hard.... the way to start it is to push the gas pedal to the floor(wide open throttle) and crank the engine.....if this "cures" your problem... replace that sensor and see how ya go.

[Cameron 77C3]

So JonJon, did ya fix this?  How about an update squire?

[2 short]

no it does not come up with any codes.
must say though if i touch the gas pedal when cranking it does start easier.
i dont think this is a good practice because i believe this may cause flooding if it doesn't fire?
i think i will go away and check that cold start sensor.
thanks

[White88]

Yes this right to an extent, opening the throttle slightly will cause flooding, but opening it all the way will help clear a flooded engine.

Extract from Corvette Fuel Injection by Charles Probst. 1982 - 2001
Clear Flood:
Corvette clear flood mode either provides a lean A/F mixture of 20:1
or completely cuts off the fuel flow so that the overrich mixture is swept out.To use Clear Flood when engine does not start, turn the ignition while holding down the accelerator. Applying Clear Flood will usually sweep out a flooded engine with air. Of course no other sensors affect the computer control of the injectors during this mode .When the engine catches, release the accelerator. When you ease off on the accelerator, the computer switches out of Clear Flood.

Yes I think you could be on to something there, the cold start sensor is temperture sensitive it's like the old fashon choke, colder it is more fuel it dumps, hotter the motor is less fuel, sounds like it's not working that well if you have more luck stating with a slightly depressed pedal.
Please post when you find the culprit.

Good luck Cheers...

[White88]

Iv'e had another thought on the subject guys.
My car has just started to do the same thing, start cold great, start hot even after leaving for several hours no good. I placed my fuel pressure gauge on , with the vaccum disconnected the fuel pressure is 44 psi, which is normal , after waiting half an hour it dropped to 20 psi ( not normal). Now I have a new fuel pump and new regulator already fitted about 4 months ago, so I suspect the leakage is coming from my injectors, which is making it hard to start because 1) there is no fuel in the rails 2) all the fuel is inside the motor (flooded). Now knowing that the cold start injector is heat sensitive the cold start injector should not be working anyway because my motor is still too warm for it to work. So if my car starts every time first up when it's stone cold  that means the cold start injector is working correctly !. If my fuel pressure didn't drop then maybe cold start sensor could've been the problem. I suspect opening the throttle slightly as 2 short was describing will help clear the flooded engine enough to help start.
I don't know if this helps or not but might be worth a look, just my 2 cents.


P.S.  2 short if want more info on checking for leaks in your fuel system -regulator, fuel pump check valve / or hole in pressure feed line and injectors just let me know, if you want a lend of my fuel pressure gauge just let me know as well as I don't live that far from you.

:<>

[2 short]

thanks for that info.
i have a fuel pressure gauge permanently fitted to the rail so i will check that out.
also noticed on saturday (very warm day) first start up for about a week i took a while to fire.