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89 Corvette wont start when warmed up.

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89 Corvette wont start when warmed up.

dullosvette dullosvette
New User | Posts: 2 | Joined: 08/10
Posted: 08/24/10
07:07 PM

I have a 89 vette and it will always start cold but once it starts and i let it sit running for a few mins and then shut it off and try to re-start, it will sound like it will crank over but will not start.....The kicker is that if i let it sit for a few mins(5-10) it will start again.I already changed out the fuel pump with strainer,fuel filter,fuel-relay,ECM, TPS, spark plugs, air filter, also had it scanned and no-codes come up? Can anybody please help me on this issue? any ideas??? Confused  

waynep7122 waynep7122
Guru | Posts: 1114 | Joined: 08/09
Posted: 08/25/10
07:18 AM

do you have a timing light????? so you can clip it around a spark plug wire... tape the trigger on.. aim it at the windshield...  see if you get spark when it fails to start...

i would also.... probably change the oil pressure switch... i will have to look... the oil pressure switches power the fuel pump.... there are 2 different versions...

oil pressure switches with 1 wire and a second with 2 wires... the one with 2 wires is for the fuel pump power...

with a 3 wire oil pressure switch..  the 2 outer wires are for the fuel pump.. the center is for the gauge...

but.. see if you get spark when it fails to start...

you might also take the time to ohm the individual injectors... there have been numerous failures with low resistance pulling to many amps and damaging the ECM...  

currently ECMs are cheep...

i have fixed a ton of ECMs and other electronics by resoldering the circuit boards... but then i know how to solder .. and have a quality weller tip controlled solder station..  not a gun... or a cheep soldering iron..

one thing.. don't breathe solder fumes... use a fan to blow them away...

you can take the ECM out.. carefully remove it from the case...  examine it with a high power magnifying lens... look for circles in the solder joints..  these circles are where the wire got hot... (a normal condition)  this expands the solder near it.. but the rest of the solder is on the board.. and the heat is absorbed.. as this center column of solder expands and contracts... it deforms the rest until it breaks away from it.. and a circle will be visible..  this is on of the reasons you can slap some electronics when they fail to work.. and get them working.. like the fonz from happy days..

but.. wait.. you already changed the ECM...    

do the timing light test.... post what you find...    if you have a fuel injection pressure tester... you might want to monitor the fuel pressure.. make sure that you are getting fuel pressure as soon as you turn the key on.. and that it stays up as the engine starts cranking...

do you have access to a scan tool...   this is a lists of sensor values..  write your engine cold values on the proper line.. and the engine hot values next to them..  then you can compare the values to see where any problems are..


one more thing to check...  but it will show up as no spark..   how does the pick up coil look.????? i have had to change a LOT of them do to just wearing out from heat cycling ..  i can post a ohm meter test for the pick up coil...  

dullosvette dullosvette
New User | Posts: 2 | Joined: 08/10
Posted: 08/25/10
01:08 PM

Thank you for your feedback this at least gives me my next step on this corvette mystery.  

radar30 radar30
New User | Posts: 1 | Joined: 08/10
Posted: 08/26/10
06:20 PM

i have a 89 vette with the same problem, it will start cold and you can run it as long as you want. when you shut it off it will not restart til it is cool. The fuel pressure is 40 , there is good spark at the plugs and there is a pulse at the injector. i scan it and there are no codes. the temp sender is reading normal.
can not figure it out.  

waynep7122 waynep7122
Guru | Posts: 1114 | Joined: 08/09
Posted: 08/27/10
05:37 AM

the temp gauge displayed on the dashboard is from a totally separate sending unit than the engine coolant temp sender... ECT..

click and open the image above... print it...  find or borrow a OBD1 scan tool... that will plug into the GM ALDL port under the dash board where you jump the a and b terminals..   you can then look at the data with a cold engine... write it down on the proper line...  then start the motor and write the data down with a hot motor and the engine running...

you will be able to see any thing thats out of range...

the sensors have to be way out of range for the check engine light to come on..  

grandsporte grandsporte
New User | Posts: 2 | Joined: 09/10
Posted: 09/20/10
03:17 PM

my 91 did that i got 2cooling sensors codes changed the senaor r/side behind dipstick and the one in frount below thermostast...  Confused been startins since  

allknight allknight
New User | Posts: 3 | Joined: 10/10
Posted: 10/10/10
05:03 AM

Has anyone fixed this problem with the '89s? I also have the exact same problem - starts cold, runs OK (not great) but when you shut it off, it cranks good, sounds like it's trying, but will not catch. It sounds like fuel, too much or too little, and flooring the throttle seems to make it worst. It MUST set for 20 minutes, then it will start. Thank goodness it's an automatic, or a clutch boo boo could leave me stuck in an intersection. I'm retired so I don't want to throw money at the problem. I have ordered some tools, fuel pressure gauge and the like, and if I solve it, I'll post the results. You too please.  

waynep7122 waynep7122
Guru | Posts: 1114 | Joined: 08/09
Posted: 10/10/10
07:36 AM

the easiest way is to print the chart above...  with all the sensor readings...

find somebody with a scan tool and examine the live data stream...

most of the time....   its the coolant temp sensor...  

at autozone... SU102   this is at the front of the TPI intake.... sticking straight forward... under the thermostat housing.. so you might have to remove something to get  at it...   the sensor with the pigtail is about 15 bucks... the connector alone is that...  please... install the connector also..    it you replace the sensor on a cold motor..  use a small pair of vice grips to pinch off the coolant overflow tube... you should not loose more than a  few ounces of coolant as long as you have not opened the cooling system...


what these do is tell the engine what the exact coolant temp is... -20 to +275F     but the sensor can go out of calibration... it happens...  it can tell the computer the engine temp is -20  or seriously hot..  

the dash board uses the sensor in the drivers side head and is totally separate from this ... the sensor in the right head is for the cooling fan override or for cars equipped with dual cooling fans it turns on the second fan....  

allknight allknight
New User | Posts: 3 | Joined: 10/10
Posted: 10/10/10
01:20 PM

After perusing lotsa posts, I find that this problem is practically an epidemic with 1989 ‘Vettes and the common denominator seems to be injectors. So I got off my butt and went out with my meter. The problem appears with a hot engine, so I started it (cold, always works) and started pulling the connectors off injectors one at a time. All had an effect, but one had much less than the rest; in fact, putting the plug back on that one had almost no effect. I then started metering each injector and found five at about 16 ohms, two at about 11, and one, the one with the least effect when unplugged, was at about 2 ohms – WOW! I then shut  off the engine, and sure enough it wouldn’t restart. Then I pulled the plug off the “bad” injector, and it started right up. This is weird enough that I shut it off and went inside, had a beer, then repeated the test about an hour later with the same results. I even drove it around the block with the injector disconnected and it restarted fine when I got home. Then I reconnected and it wouldn’t start. Methinks the ECM is reacting to that shorted injector by denying fuel to all injectors.
Finally, I let the car sit for a few hours and metered the “bad” injector cold – 10 ohms! The lesson is that if the problem occurs hot, do your testing hot.
It looks like I’m in the market for some Bosch III’s.  

allknight allknight
New User | Posts: 3 | Joined: 10/10
Posted: 10/21/10
12:37 PM

In closing, I installed a set of Bosch design-3's from Fuel Injection Connection and now the Vette runs and starts like a new car. I think anyone suffering from hot restart problems should first get a good meter and check for a shorted injector. If you borrow or already have a meter that can accurately read below 10 ohms, the test is quick and free. If all injectors read above 12 ohms (16 is best), then you can look elsewhere.  

rockr15 rockr15
New User | Posts: 1 | Joined: 10/10
Posted: 10/22/10
03:55 PM

I have the exact same problem with my 69 vette.  Starts right up cold and runs great; but if you shut it off and try to restart it again, it won't start.  Let it set for 10-20 minutes or so -- no problem.  Starts right back up.  Weird thing is, if you give the starter a few good taps with a hammer, it'll turn over.  So, we replaced the starter.  Still having the same problem.  I installed a heat shield between the starter and the exhaust, thinking that heat might be the problem but that didn't fix it either.

Anybody have any suggestions?  Makes it difficult to try to get thru emissions.  They're not big on letting it sit for 10 minutes.  They just push me out the other side and say come back later.  Frown  

waynep7122 waynep7122
Guru | Posts: 1114 | Joined: 08/09
Posted: 10/22/10
07:01 PM

lets step back...   a 69 has a carb... the 89 fuel injection problems..

i am taking that your starter is failing to crank hot....

and thats NOT uncommon...

how close to original or restored is your 69...

let me describe the cranking circuit..

the battery cable to the top post on the starter...  then up through a smaller wire to either the horn relay.. or through the bulk head connector to the amp meter,, then to the ignition switch.. the neutral safety switch.. back through a bulk head connector...  and down to the S terminal on the starter solenoid...

it takes over 50 amps of power to pull the starter solenoid plunger in hard enough to bump the contact button at the back of the solenoid.. pushing this spring loaded button moves the contact disc across the terminals to make the starter spin...

you really need to shorten the path.. or take the affected wiring apart and verify the connectors are NOT BURNED OR DAMAGED..

i usually install a relay in the big purple wire to the starter solenoid... using the existing wiring to operate the relay.. but supplying the power for the relay contacts with power from the starter top post...

almost all new cars use a load dropping relay to power the starter solenoid..

if your car is totally original..  or completely restored.. you might want to take apart the connectors and clean them.. verify the circuits... it could be in the switches also..

i usually grab some HIGH temp fiberglass strand insulated wire.. 10 gauge...  some proper ring terminals..  

i run a 10 gauge wire from the top stud on the solenoid to the relay pin 30..

then from pin 87A to the S terminal...

a ring terminal on a 14 or 16 gauge wire with a small nut and bolt to attach the old wire that was on the S terminal to the new smaller wire to control the solenoid pin 85.. and pin 86 to ground..

using a quality relay...  on non original cars .. i like to use a 70 dodge dart starter relay..  as they are designed for this duty..  and have a nice bracket that i bolt to the bottom of the heater box studs sticking out the firewall.. ..

now.. it is also possible to stash a relay under the dashboard... to shorten the circuit length from the battery..

quality mini starters can also be installed...  their internal solenoids require less amperage to pull in and bump the contact disc...

use a quality NAME BRAND.. mini starter...  some of the generics leave a big to be desired..  but again.. is it original..    if one was really sneaky.. one might be able to stash a relay out of sight..  so it would not be seen..