Idle issue

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Idle issue

Postby fvkagi » Wed Jan 01, 2020 6:57 pm

Hello,

I am having issues with my ST185 project not idling correctly, it will start fine and idle at ~2000 for 5 seconds then the car will die.

I have replaced the IAC and the TPS. I also did a boost leak test and fixed all of those as well.

I am now thinking it is either a wiring issue, but I was wondering if it could be the o2 sensor? Does anybody know how quickly a ST185 will change from open loop to closed loop idle?

Any ideas and/or suggestions are welcome!
Thanks! :)
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Re: Idle issue

Postby 93celicaconv » Wed Jan 01, 2020 7:58 pm

5 seconds after startup on a cold start is not sufficient time for the ECU to go from open to closed loop control.

Based on very little information in your analysis thus far, it is possible you are able to start the engine with the fuel sourced from your cold start injector alone, and after that shuts down when the engine has started, if not fuel is coming from the regular fuel injectors, I can see the engine shutting down around 5 seconds after cold start.

Do you have a check engine light on? Regardless, you should check the ECU for DTCs and if any are present, deal with the diagnostics of the code(s) found.

If no DTCs and no check engine light, remove the cold start injector wiring harness connector from the cold start injector and try starting it again. Does it start? If not, I would try to understand why your injectors are not operating.

Since the engine starts initially and runs fine for a short period, I suspect your air and fuel systems are operating normally, so I would focus on the electronic control aspect.

This may be a dumb question, but since you called it a "project" ST185, I'm assuming you've done some work on it. Is the fuel injector solenoid resistor properly connected to the wiring harness? If not connected, or not connected properly, that would disable all 4 of your fuel injectors.
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Re: Idle issue

Postby fvkagi » Wed Jan 01, 2020 8:23 pm

93celicaconv wrote:5 seconds after startup on a cold start is not sufficient time for the ECU to go from open to closed loop control.

Based on very little information in your analysis thus far, it is possible you are able to start the engine with the fuel sourced from your cold start injector alone, and after that shuts down when the engine has started, if not fuel is coming from the regular fuel injectors, I can see the engine shutting down around 5 seconds after cold start.

Do you have a check engine light on? Regardless, you should check the ECU for DTCs and if any are present, deal with the diagnostics of the code(s) found.

If no DTCs and no check engine light, remove the cold start injector wiring harness connector from the cold start injector and try starting it again. Does it start? If not, I would try to understand why your injectors are not operating.

Since the engine starts initially and runs fine for a short period, I suspect your air and fuel systems are operating normally, so I would focus on the electronic control aspect.

This may be a dumb question, but since you called it a "project" ST185, I'm assuming you've done some work on it. Is the fuel injector solenoid resistor properly connected to the wiring harness? If not connected, or not connected properly, that would disable all 4 of your fuel injectors.


I call it a project because I bought it non running with some body damage hah.

Anyways, I have code 51, but I believe it is because the PO removed the AC from the car.

I will definitely look at the injectors, the wiring looks suspect it has extra injector plugs just spliced into the harness for some reason (some brown and some orange if that means anything).

But, I can also rev the car up, is it possible to be doing this with just the cold start injector working? Thanks for the help.
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Re: Idle issue

Postby 93celicaconv » Wed Jan 01, 2020 11:47 pm

Pics of your current situation would be very helpful. Otherwise, disconnect the cold start injector and see if it starts at all. If not, you are pretty close to solving your problem.

What is the temperature in your location, and are you outside or in a garage?
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Re: Idle issue

Postby underscore » Thu Jan 02, 2020 6:05 am

Try jumping FP and B+ in the diagnostic box to bypass the fuel pump circuitry, it kinda sounds like it isn't staying on properly. When my car had a bad vac leak and only the cold start was keeping it running it lasted more than 5s before dying and I wouldn't think you'd be able to rev it up just on the CSI.
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Re: Idle issue

Postby Andy » Thu Jan 02, 2020 2:36 pm

Make sure the AFM is plugged in good. I've seen the start die... more than once when the AFM is unplugged...
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Re: Idle issue

Postby fvkagi » Thu Jan 02, 2020 7:41 pm

93celicaconv wrote:Pics of your current situation would be very helpful. Otherwise, disconnect the cold start injector and see if it starts at all. If not, you are pretty close to solving your problem.

What is the temperature in your location, and are you outside or in a garage?


Here is an imgur album of the injector plugs that are just sitting around
https://imgur.com/a/qi0zTzQ

Also is the cold start injector under the throttle body or is it the plug going into the IAC?
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Re: Idle issue

Postby 93celicaconv » Thu Jan 02, 2020 8:01 pm

Attached is a schematic view of the cold start injector setup. I believe it attached on the underside of the intake manifold. I've also provided a pic of where it is - it is mostly hidden in the pic, but the fuel line attaching to it, and the wiring harness connector, are clearly visible.
Attachments
Cold Start Injector.jpg
ST185 Cold Start Injector.jpg
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Re: Idle issue

Postby Magroo » Thu Jan 02, 2020 11:33 pm

underscore wrote:Try jumping FP and B+ in the diagnostic box to bypass the fuel pump circuitry, it kinda sounds like it isn't staying on properly. When my car had a bad vac leak and only the cold start was keeping it running it lasted more than 5s before dying and I wouldn't think you'd be able to rev it up just on the CSI.


Id like to second this. Its possible your fuel pump relay is cooked.

Also right before my ecu died it was doing something similar. Might want to crack it open to see if there are any leaking capacitors.
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Re: Idle issue

Postby fvkagi » Fri Jan 03, 2020 6:00 pm

underscore wrote:Try jumping FP and B+ in the diagnostic box to bypass the fuel pump circuitry, it kinda sounds like it isn't staying on properly. When my car had a bad vac leak and only the cold start was keeping it running it lasted more than 5s before dying and I wouldn't think you'd be able to rev it up just on the CSI.


This worked!

So this means the fuel pump relay is cooked lol
Can I just buy it as a universal Toyota part?

Thanks for the help! :)
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Re: Idle issue

Postby underscore » Fri Jan 03, 2020 6:36 pm

Look up the diagrams on here and work your way through the fuel pump circuit in the section the jumper bypasses. The fault may lie with something other than the relay.
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Re: Idle issue

Postby Magroo » Sat Jan 04, 2020 12:24 am

fvkagi wrote:
underscore wrote:Try jumping FP and B+ in the diagnostic box to bypass the fuel pump circuitry, it kinda sounds like it isn't staying on properly. When my car had a bad vac leak and only the cold start was keeping it running it lasted more than 5s before dying and I wouldn't think you'd be able to rev it up just on the CSI.


This worked!

So this means the fuel pump relay is cooked lol
Can I just buy it as a universal Toyota part?

Thanks for the help! :)


When I replaced mine it was like $75 from the dealership. I'd still go through the wiring and fuel pump resistor to make sure it isnt something else.

The relay is just a single pole double throw thats used to put the fuel pump in to a high or low output state.
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Re: Idle issue

Postby 93celicaconv » Sat Jan 04, 2020 12:58 pm

Underscore, great recommendation - you were spot on.

If it helps, the fuel circuit wiring diagram from the ST185 may be found in the attached - should make walking through the system a bit more clearer. I would say there is also a chance the fuel pump resistor has open circuited (perhaps not plugged in), so when the ECU switches from high pressure (start) to low pressure (after start), an open resistor in that part of the circuit cuts out the fuel pump. That may also tie to the 5 seconds after startup when the engine stalls. But that is just a guess - I don't know actually how the ECU controls that fuel pump resistor via the fuel pump relay.
Attachments
ST185 Fuel System Wiring Circuit.jpg
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Re: Idle issue

Postby fvkagi » Sat Jan 04, 2020 4:43 pm

93celicaconv wrote:Underscore, great recommendation - you were spot on.

If it helps, the fuel circuit wiring diagram from the ST185 may be found in the attached - should make walking through the system a bit more clearer. I would say there is also a chance the fuel pump resistor has open circuited (perhaps not plugged in), so when the ECU switches from high pressure (start) to low pressure (after start), an open resistor in that part of the circuit cuts out the fuel pump. That may also tie to the 5 seconds after startup when the engine stalls. But that is just a guess - I don't know actually how the ECU controls that fuel pump resistor via the fuel pump relay.


Thanks for the diagram, I believe it is the resistor because I removed the relay and it was clicking when I applied voltage. I will check to see if the resistor has an actual resistance to it hah
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Re: Idle issue

Postby underscore » Sat Jan 04, 2020 7:08 pm

I opted to use the jumper from a 5SFE in place of the relay to bypass the resistor system. If the fuel system cuts out or switches to the wrong mode at the wrong time the results could be catastrophic, and by all accounts here the only supposed benefit is reduced fuel pump wear. When everything was shiny and new I'd have no problem with it but when parts are approaching 30 years old simplicity seems safer.
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