Input on hot start failure - ZR-1 Net Registry Forums

onetinsoldier · 06-10-2018

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 · 06-10-2018

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

onetinsoldier · 06-11-2018

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 · 06-13-2018

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 · 06-13-2018

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 · 06-13-2018

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 · 06-13-2018

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 · 06-13-2018

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 · 06-14-2018

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 forget the acronym just now].

This is getting interesting...one for the log books!

BTW, what year Z are we dealing with?

onetinsoldier · 06-16-2018

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 !

06-10-2018	#1
onetinsoldier Join Date: Aug 2016 Location: Spring Hill, FL Posts: 127	Input on hot start failure - Update 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 ? .................... Last edited by onetinsoldier; 07-28-2018 at 08:07 AM. Reason: UPDATE !

06-10-2018	#2
JG95ZR1 Join Date: Aug 2017 Location: Queens, NY Posts: 166	Re: Input on hot start failure 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

06-11-2018	#3
onetinsoldier Join Date: Aug 2016 Location: Spring Hill, FL Posts: 127	Re: Input on hot start failure 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 !

06-13-2018	#4
QB93Z Join Date: May 2007 Location: Westminster, Maryland Posts: 3,684	Re: Input on hot start failure 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

06-13-2018	#5
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,466	Re: Input on hot start failure 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.

06-13-2018	#6
onetinsoldier Join Date: Aug 2016 Location: Spring Hill, FL Posts: 127	Re: Input on hot start failure 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 ! Last edited by onetinsoldier; 06-13-2018 at 07:36 PM.

06-13-2018	#7
QB93Z Join Date: May 2007 Location: Westminster, Maryland Posts: 3,684	Re: Input on hot start failure 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

06-13-2018	#8
onetinsoldier Join Date: Aug 2016 Location: Spring Hill, FL Posts: 127	Re: Input on hot start failure 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 .

06-14-2018	#9
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,466	Re: Input on hot start failure 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 forget the acronym just now]. This is getting interesting...one for the log books! *BTW, what year Z are we dealing with?* Last edited by Paul Workman; 06-14-2018 at 08:46 AM.

06-16-2018	#10
onetinsoldier Join Date: Aug 2016 Location: Spring Hill, FL Posts: 127	Re: Input on hot start failure 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 !