Input on hot start failure

[onetinsoldier]

Ok If I drive for more than 30 min and I park the car , If I dont wait at least 30 min it wont start . The starter turns it , it has spark , but no start .

Now I removed a vacuum line on the plenum and spray carb clean in it , it starts , if I turn it off and try to start with no carb clean , no start by itself .

Obviously its a fuel issue , but what's causing it ? I'm wondering coolant temp sensor ? ....................

[JG95ZR1]

Sounds like fuel pumps. At cold start both pumps are running once the engine heats up it works on one pump unless secondary injectors are activated. If you get your hands on a fuel pump bypass harness install it the next time the car doesn’t start. Once you install harness the secondary pump will turn on and the car should start up, if it does not start the issue is not the pumps.


Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

[onetinsoldier]

That makes sense . I will see if I can tie a wire to the 2nd fuel pump and have the other end to jumper to a power source so i can test it !

[QB93Z]

I am not sure you have a fuel pump problem from the symptoms you have described.


When you try to start the car when it is hot does it never fire at all OR does it start and then stop 3 seconds later?


When you use the Carb Cleaner to get it to start, does it continue to run normally? If so, it would seem that the fuel pumps are OK.


Jim

[Paul Workman]

FAILURE WHEN HOT = classic electrical (usually windings) issue. But, the answer to Jim's question needs to be known before going further: IOW, are the injectors being commanded to fire?

But, in the mean time keep these steps in mind:


There is a little red wire and connector jutting out of the wire harness about where the windshield motor is = the fuel pump test connector.

With a pressure gauge on the fuel rail and the ignition switch OFF, set up your VOM for AMPERES and put the red lead on the POS battery terminal and clip the black lead to that little connector.

Each pump normally draws between 4-5 amperes, and therefore should read 8-10A on the VOM. Fuel pressure should be 45 (ish ±). After removing the VOM from the test connector, pressure should remain to within a pound or two for several (15) min.

[onetinsoldier]

Yes after spraying carb clean in it , it starts and continues to run .Now whether or not the injectors are spraying at hot start, I have no way of telling . I have checked the fuel pressure for each individual pump and they are fine . I have the service manual , and have read and tried what it says to test with what tools I have . I have no scan tool to see whats going on !

[QB93Z]

The big three: air - fuel - spark.


I would look at spark. Check for some weak sparking: coils, wires and plugs. Check for tracking on the plugs which indicates the spark is jumping to the head instead of sparking in the combustion chamber. Clean each plug and add some di-electric grease to the inner surface of each plug wire boot.


Jim

[onetinsoldier]

I have tested the spark also , plenty of spark ! So you know I am not new to auto repair , I rebuilt my first engine when I was 13 , I am 59 now and just do it as a hobby !

I have checked all the basics , which are pretty much all the same in every engine . In the past I have had a lot of fuel problems solved , by replacing the temp sensor , it tells the computer whats going on, along with other sensors .

[Paul Workman]

If fuel pressure at the rail is good (45 ish) upon initializing the starter...and no fire unless you prime the motor first...I seem to want to want to know for sure if the injectors are firing at startup?

NOT meant as an insult - just me crossing the "Ts" and dotting the "Is", but if the accelerator is pressed to the floor on startup, the injectors are cut off as part of the "clearing flooded engine" routine. Assuming you're NOT touching the gas when cranking, I'm curious as to what the TPS voltage is a zero throttle? (And, from zero % to WOT, does the voltage progress smoothly w/o any "holes/glitches" along the entire range?

Dayam... a scanner or pooter S/W or a paper clip/ALDL readout might reveal a clue or two.

FWIW, the two coolant sensors are on the left cylinder bank, toward the front, under the plenum. One is for the gauge and the other for the ECM.

The FSM provides a procedure for observing the ECM's temp sensor using the buttons on the (display control center) .

[I]This is getting interesting...one for the log books!

BTW, what year Z are we dealing with?

[onetinsoldier]

It is a 91 Z . About 70k on the odometer . I do drive it on full power , the car doesn't like driving with it off !

[Ccmano]

It is a 91 Z . About 70k on the odometer . I do drive it on full power , the car doesn't like driving with it off !

Tell us more about how it drives with the key off.
H
:cheers:

[onetinsoldier]

It drives behind my truck on a trailer !

[onetinsoldier]

It's also getting close to being posted on Craigslist ! Cause I'm about done with it ! I drove it today it took an hour and 20 min before it would start !

[onetinsoldier]

Ok , an update I replaced the fuel pumps just to rule out hot pump failure and also the crank position sensor which was a suggestion . It starts quicker on a cold startup but you have to wait an hour and a half after driving it ! Any more suggestions ? Is there someone near Spring Hill Fl that has a scanner and knows what to look for ?

[Ccmano]

So after you run the car and stop it, during the hour and a half when it will not start, will the engine turn over and not start or does it just not even turn over?
H
:cheers:

[Dynomite]

So after you run the car and stop it, during the hour and a half when it will not start, will the engine turn over and not start or does it just not even turn over?
H
:cheers:

Ok If I drive for more than 30 min and I park the car , If I dont wait at least 30 min it wont start . The starter turns it , it has spark , but no start .


:happy1:


It starts with carb cleaner and will continue to run hot or cold.
It has fuel pressure both pumps.
It has to be injectors are not firing during a HOT start....why.....I have no clue :p

[XfireZ51]

Can you tell us when this situation started?

[onetinsoldier]

This has been going on about 4 yrs . I did replace the ecm a couple of years ago , but it was doing it before then . Cold start has no issues . after driving say over 10 miles , park , turn it off , try to start it , engine spins over , no start . it has fuel pressure. it has spark.
.
Now i replaced the crank sensor a couple of days ago and the metal plate was not allowing it to fully seat, I removed the plate , but still have the same issue . I know if you floor it , it stops the injectors , and I normally dont push the pedal to give it fuel on any of my cars except the race ones . Maybe this is the hot start problem ? How many of you crack the throttle on hot starts to get your zr1 to start ?

[XfireZ51]

1. So swapping out the ECM did not clear up the problem?

2. When u start cold, have u turned key to ON and heard the pumps energizing?

3. Have u done that w engine hot, say after 30 min? Do pumps energize then?

4. It would be interesting to have a scantool on the car in both instances to see if u r getting any injector pulse. Apparently u must be when cold, how about hot?

5. Have u noted what the coolant temp is when u can resume restarting motor?
Obviously it won’t be ice cold, so it will be warm but at what temp?

BTW, “flying height” on crank sensor is important.

[onetinsoldier]

I have no scan tool , so I have no idea what temps , pulses , signals it may or may not be getting . I have no fuel pressure problem , I have a digital fuel pressure gauge mounted inside the cabin . It seems that whatever pulse should be sent to inject fuel , isnt being sent when its hot .

I am going to try driving it again , get it hot , park it and try cracking the throttle to restart it . I didnt think you needed to give it gas , always thought it was initiated by the ecm .

[XfireZ51]

... It seems that whatever pulse should be sent to inject fuel , isnt being sent when its hot .

I am going to try driving it again , get it hot , park it and try cracking the throttle to restart it . I didnt think you needed to give it gas , always thought it was initiated by the ecm .

No I never give mine gas. Shouldn't need to. If the motor is hot, it usually lights in a couple of rotations.

That was the point I was trying to get at. Your injectors obviously work ONCE the motor gets going or when it is cold. The cam sensor is what sends the signal for pulsing the injectors. It synchronizes the fuel pulsing with the ignition firing by determining when #1 is in position for combustion.
With a datalogger, you could see if the injectors are indeed pulsing during startup for hot and cold starts.

[Ccmano]

Let’s see, what do we know....

- It will start and run when cold.
- Once hot it will turn over but not start.
- It does not run (well) with the power key in the low power setting.
- Fuel pressure is normal, pumps are new.
- The crank sensor is new and did not affect the condition. It may not be properly seated?
- ECM is relatively new.

Are the injectors original or are they replacements? If they are original, have you ohm’d each one to see if they are good.
http://www.zr1specialist.com/HAT%20Web/articles/Measuring%20Fuel%20Injector%20Resistance%20with%20 the%20Plenum%20in%20Place.pdf

Is the system showing any codes? (Paper clip on the ALDL connector. https://www.obd-codes.com/faq/read-gm-2-digit-obd-codes-free.php) Is the SES light on? I’m guessing not.

The fact that it barely runs, if at all, in the low power mode may be a clue. In this mode the secondaries are totally inactive.

I’m starting to suspect the primary injectors. Running when cold but not hot is classic injector failure. On the other hand bad coils do the same thing.

Still without more basic system data diagnosis will be difficult.

There are two shops in FL. that should be able to handle it. But they are not around the corner from you.

Corvette Masters in Orlando and Eismanns Corvette Center in Jupiter.

H
:cheers:

[onetinsoldier]

Ok I may be on to something here , it seems after driving and its hot , if i just put a little weight on the gas pedal , it will start . Could it be the throttle blades need to be opened some ? I normally dont give it any fuel by pedal when I start it either cold or hot .

[QB93Z]

One possibility is that the throttle body gasket was not cut properly and there is no hole to allow air through the IAC (Idle Air Controller). I have seen that happen.


Another thing might be a stuck shut IAC valve.


You are becoming a good automotive detective!


Good luck, Jim

[Ccmano]

Or simply a bad or misadjusted throttle position sensor. The system looks for a proper throttle position reading as part of the starting sequence.
H
:cheers:

[onetinsoldier]

I believe the tps is set .54 . All I know is this is getting old , and if I cant solve it soon , its going up for sale ! I dont like having a car thats not dependable. A friend of mine that owns a corvette shop , told me not waste my money buying a c4 zr1 . But I wanted one , maybe he was right !

[Ccmano]

I believe the tps is set .54 . All I know is this is getting old , and if I cant solve it soon , its going up for sale ! I dont like having a car thats not dependable. A friend of mine that owns a corvette shop , told me not waste my money buying a c4 zr1 . But I wanted one , maybe he was right !

True, these cars are not for everyone. In reality you can’t drive a 28 year old car and expect it to be perfectly reliable. Some may be, but you can’t expect that.

How do you know the TPS is at .54v?
H
:cheers:

[XfireZ51]

Might be cheaper to have one of fly down and bring some tools to work w u on the car.

[Hib Halverson]

Do you have the Factory Service Manual for a 91?

That digital FP gauge you have...when you are key-on/engine-off, what does it read?

Also, do you have a noid light?

[onetinsoldier]

Well giving it gas pedal has failed ! I did replace the coolant temp sensor , gave me the chance to repaint the plenum !
Anyway , Pressure reads about 58psi ,key on , engine off . And there is no reason why it cant be reliable , I have 55 chevys that start every time ,of course no electronics !
I'm not sure if the local chevy dealer still diagnose this cars or not ? I may see if they can scan it and tell me whats going on !

[onetinsoldier]

Or simply a bad or misadjusted throttle position sensor. The system looks for a proper throttle position reading as part of the starting sequence.
H
:cheers:

I use a digital ohm meter , its .54 !

[XfireZ51]

Ok.

1. When u turn ignition ON, engine COLD you hear both pump energizing, Correct?

2. When you turn ignition ON, engine HOT , you hear both pumps energizing, CORRECT?

3. Have u determined at what coolant temp, the warmed motor will finally start at?

[onetinsoldier]

well after replacing the crank sensor and no luck , I tried another crank sensor , it seems to have solved the problem ! ....hopefully !