Wont start after driving for a while..

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Re: Wont start after driving for a while..

Postby maxaud » Sat Feb 18, 2017 8:32 pm

Was having the issue of not starting this weekend so I bridged the Fp and B+ in the diagnostic port and it started right up. Maybe it's the fuel pump relay but if it's going bad, I'm curious if there is something somewhere else that is making it go bad.
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Re: Wont start after driving for a while..

Postby FC Zach » Mon Feb 20, 2017 3:00 am

maxaud wrote:Was having the issue of not starting this weekend so I bridged the Fp and B+ in the diagnostic port and it started right up. Maybe it's the fuel pump relay but if it's going bad, I'm curious if there is something somewhere else that is making it go bad.


It's definitely your relay. I asked the same question about the cause, this is the response I got:

yyonline wrote:Usually it's just the relay that's bad. What usually happens is that something causes its internal resistance to go up (cracked solder joint, corrosion, etc.). When the resistance goes up, it generates more heat. Which causes more damage, which generates more heat, that causes more damage...etc. until it fails.

It's also possible that the fuel pump has high internal resistance which is causing too much current to pass through the relay and that's why it overheated. But the first scenario is more likely.
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Re: Wont start after driving for a while..

Postby FC Zach » Mon Feb 20, 2017 3:04 am

Forewarning, that relay is not cheap so be prepared to spend $90. . . unless you plan on replacing it with a "good" used part but you'll probably be in the same boat again.
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Re: Wont start after driving for a while..

Postby underscore » Mon Feb 20, 2017 5:19 am

Is there some special functionality it has or is it just like a normal relay?
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Re: Wont start after driving for a while..

Postby FC Zach » Mon Feb 20, 2017 5:23 am

Looks like any other relay, like the e-fan relay for example but rated for different load.

EDIT: I looked at mine while checking things under the hood last weekend. . . It's nothing like the fan relay, or any other relay. It's a completely different size. Also, it's the yellow one. . I say this because if it's getting excessively hot from too much resistance it will discolor and if like mine, it'll turn brown (as seen on the previous page).
Last edited by FC Zach on Wed Mar 01, 2017 6:14 am, edited 1 time in total.
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Re: Wont start after driving for a while..

Postby FC Zach » Mon Feb 20, 2017 5:24 am

And for whatever reason, it cost way too much!
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Re: Wont start after driving for a while..

Postby underscore » Mon Feb 20, 2017 5:37 am

In that case I'd just take apart the old relay and gut it, then wire it as the plug for a socket for a standard relay, allowing it to plug in without messing with the factory harness.
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Re: Wont start after driving for a while..

Postby FC Zach » Mon Feb 20, 2017 5:42 am

underscore wrote:In that case I'd just take apart the old relay and gut it, then wire it as the plug for a socket for a standard relay, allowing it to plug in without messing with the factory harness.


That would be a great idea if you can find a suitable relay to put in its place.
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Re: Wont start after driving for a while..

Postby alltracman78 » Tue Feb 21, 2017 1:45 am

FC Zach wrote:
maxaud wrote:Was having the issue of not starting this weekend so I bridged the Fp and B+ in the diagnostic port and it started right up. Maybe it's the fuel pump relay but if it's going bad, I'm curious if there is something somewhere else that is making it go bad.


It's definitely your relay. I asked the same question about the cause, this is the response I got:

yyonline wrote:Usually it's just the relay that's bad. What usually happens is that something causes its internal resistance to go up (cracked solder joint, corrosion, etc.). When the resistance goes up, it generates more heat. Which causes more damage, which generates more heat, that causes more damage...etc. until it fails.

It's also possible that the fuel pump has high internal resistance which is causing too much current to pass through the relay and that's why it overheated. But the first scenario is more likely.


High internal resistance in the pump would allow less current in the circuit and less heat at the relay.
The heat probably comes from higher resistance at the contact. Now if the pump had less resistance, that would cause more current in the circuit and more heat at the relay [especially if the contact is damaged at all].

A relay is a switch. Every time a switch opens and closes a tiny bit of material is "pulled" off one side and sticks to the other. You also get some "burning" on the 2 sides. So you're pitting and coating the surfaces with carbon every time the switch opens and closes. The amount of damage depends on the voltage, current, design and amount of use [opening and closing]. Same thing happens with your starter contacts.

Most likely the contacts are just worn out, causing heat. If they're worn out they also won't necessarily always work [like your starter contacts].

There is another option to the relay [specifically the high/low speed pump relay]. In the 5sfe cars there is no relay, they use a jumper so it's always on "high". It pulls right out and plugs right into our cars. Your pump will always be on "high". Not really a problem IMO. The jumper is in the same exact spot as our relay.
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Re: Wont start after driving for a while..

Postby FC Zach » Tue Feb 21, 2017 4:04 am

alltracman78 wrote:There is another option to the relay [specifically the high/low speed pump relay]. In the 5sfe cars there is no relay, they use a jumper so it's always on "high". It pulls right out and plugs right into our cars. Your pump will always be on "high". Not really a problem IMO. The jumper is in the same exact spot as our relay.


Thanks for this, this is good to know if it were to ever happen down the road. . next time I'm at the scrap yard I'll keep an eye out for a GT. This is something I'll keep in my emergency bag.
1992 Toyota Celica AllTrac
1987 Mazda RX7 Sport
1979 Yamaha G1A, rotary powered with Sachs KM24
1976 Hercules W2000, oil injected
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Re: Wont start after driving for a while..

Postby maxaud » Tue Feb 28, 2017 7:03 pm

Took this to my local Auto Electric location who are pretty good with electrical items and they're telling me the ECM isn't always signaling the fuel pump to turn on and recommend putting a new ECM. Looks like the ECMs are different between USDM and JDM. I found the pinout diagram for the st185H CS, I assume it's the same as the st185H RC? Anyone have a JDM one laying around part number 89661-2B310?
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Re: Wont start after driving for a while..

Postby underscore » Tue Feb 28, 2017 11:38 pm

Did they open is up and take a look at the capacitors? Given the age of these cars they're likely to start drying out.
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Re: Wont start after driving for a while..

Postby FC Zach » Tue Feb 28, 2017 11:54 pm

underscore wrote:Did they open is up and take a look at the capacitors? Given the age of these cars they're likely to start drying out.


Yep, I've had this happen too.
1992 Toyota Celica AllTrac
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1979 Yamaha G1A, rotary powered with Sachs KM24
1976 Hercules W2000, oil injected
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Re: Wont start after driving for a while..

Postby FC Zach » Wed Mar 01, 2017 6:06 am

You may be able to repair yours. Not the case for me, unfortunately I had to replace this ECU since the tracers were burnt too.

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1992 Toyota Celica AllTrac
1987 Mazda RX7 Sport
1979 Yamaha G1A, rotary powered with Sachs KM24
1976 Hercules W2000, oil injected
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Re: Wont start after driving for a while..

Postby maxaud » Wed Mar 01, 2017 6:05 pm

Anyone known which ones can be interchanged with the one I have. 1992 ST185H with W2A Intercooler.
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