87 supra starting issue

Parch1059

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#1
Will start at first after an hour will not restart, but can push start it or wait until the next day for it to start, any ideas what is the issue and how too fix it?
 

plaaya69

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#5

Nick M

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#9
Sounds like you should do the 12v starter mod. Does the Supra turn over at all after a hour?
This is why the internet needs to bring back the down vote, and then shade the user comment so others it is bullshit.
 

suprarx7nut

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#10
The issue term here is "hot start". That may be a good term for you to search.

Forget the "12V starter mod". That's a hack repair. OP also has good cranking so that's not the issue here.

There's a VSV responsible for "Fuel Pressure Up". It increases fuel pressure for high temp starts. If it is malfunctioning it can be very difficult to start a warm engine. See the description here: http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=45

Check the VSV, check the water temp sensor and air temp sensor. Check for codes. If the car runs well aside from hot start, my guess is you have a fault in the fuel pressure up system.

This is why the internet needs to bring back the down vote, and then shade the user comment so others it is bullshit.
Agreed. Reddit is an excellent showcase of the power of such a feature. Negative voted comments are automatically hidden. It's only as good as the "hivemind", but at least an errant comment early in a thread gets quickly hidden. In contrast with old school forums like this where the early comments will forever be the most read.
 

plaaya69

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#11
This is why the internet needs to bring back the down vote, and then shade the user comment so others it is bullshit.
Well it does not help when the original poster does not give a better detailed explanation of what exactly is going on such as a cranking, fuel or ignition problem so I will provide a short theory until there is more information provided (which he has now). How about you contribute something useful to the thread starter as your comment seems about as useless as mine?

Forget the "12V starter mod". That's a hack repair.
The 12v starter mod is not a hack repair and I despise hack jobs myself but it is a common problem with other mk3 Supra owners going way back. There has been no real solution for this problem even with new starters, relays, ignition switches and good wiring. The slightest voltage drop through the long path it takes on that starter circuit seems to cause problems so why would you not want a shorter current path with better voltage to your stater solenoid? A hack job to me seems like jamming bare wire in-between your fuse and fuse box when you do a fog light rewire.
 
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JDMMA70

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#12
99% of the time its not any of the components or wiring but rather the connector terminals being oxidized or corroded. If you can figure out where the voltage drop is occurring and clean the terminals between the two points. It generally fixes the issue. However I can only speak from my own experience.
 

suprarx7nut

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#13
Well it does not help when the original poster does not give a better detailed explanation of what exactly is going on such as a cranking, fuel or ignition problem so I will provide a short theory until there is more information provided (which he has now). How about you contribute something useful to the thread starter as your comment seems about as useless as mine?



The 12v starter mod is not a hack repair and I despise hack jobs myself but it is a common problem with other mk3 Supra owners going way back. There has been no real solution for this problem even with new starters, relays, ignition switches and good wiring. The slightest voltage drop through the long path it takes on that starter circuit seems to cause problems so why would you not want a shorter current path with better voltage to your stater solenoid? A hack job to me seems like jamming bare wire in-between your fuse and fuse box when you do a fog light rewire.

The real solution is to hunt down the voltage drop root cause by checking voltage along the entire circuit path. After more than a decade with 4 of these cars and over 100k miles driving them I've never seen it be the actual wire. It's normally a connection point somewhere or a faulty relay (in the pass kick panel if my memory is right). Jetjock had far more experience than I and had similar findings - it's never the wire. The 12V mod just replaces a bunch of OEM components with a very basic relay setup. Over time, I'm confident an auto parts store relay in the engine bay will be unreliable.

Fix it right and find the true root cause.
 

3p141592654

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#14
Agreed. If there is a no crank issue then a voltage drop test is the way to debug it. As a very basic check, you should hear the fuel pump turn on when you try to crank. If the problem is limited to hot starts then the starter solenoid is suspect. Other problem areas are the ignition switch, theft deterrent relay, and the NSW and associated connectors.

Note that these cars started reliably for years when new, so you don't need to add hardware to restore to a reliable starting system.
 

trydrew

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#15
I had a similar issue with a NG CPS. It was such that if the car were shut off after getting to temperature, I could not restart it, sometimes for hours. I replaced it with a spare CPS I had, making no other changes, and I haven't had the issue since.

In my case, when hot, the ECU was not getting the RPM signal from the CPS (do not know exactly why), and thus the fuel pump wouldn't fire. As soon as the car sat long enough you would finally see the tach start to jump, and subsequently, the car would fire right up with no further hesitation.

Also note, the NG CPS had new connectors and pin, as did the mating harness, but the wires themselves were not replaced.

Edit: Suppose this could just be for reference.. just crossed my mind, can't push start if there's no RPM signal.. doh.
 

Jonnymkiii

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#16
^ What trydrew said.. I suspect it's the CPS. I doubt it's the plug connector on the CPS since it will restart when the engine cools down; although Driftmotion sells replacement plugs. I've had this exact same problem with the AEM v2 because the CPS signal was too low when the internal magnets were hot.

Try running it for a bit to get it up to operational temperature and park it at your home and if you are able to duplicate the issues, see if you're getting spark. If you are not, the ECU most likely isn't getting the timing signal from the CPS.

If you don't have another CPS to try, it wouldn't hurt to see if the Driftmotion magnet mod makes a difference.