Idle issue

fvkagi

Member
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! :)
 
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.
 

fvkagi

Member
93celicaconv":ra8chgwe said:
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.
 
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?
 

underscore

Well-known member
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.
 

Andy

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

fvkagi

Member
93celicaconv":22jj9hta said:
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?
 
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.
 

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Magroo

New member
underscore":1ee3pnd9 said:
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.
 

fvkagi

Member
underscore":ufajgdui said:
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! :)
 

underscore

Well-known member
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.
 

Magroo

New member
fvkagi":tuw86f8h said:
underscore":tuw86f8h said:
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.
 
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.
 

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fvkagi

Member
93celicaconv":37jt2y5a said:
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
 

underscore

Well-known member
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.
 

fvkagi

Member
underscore":3ijosi7d said:
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.

I like the sound of this option, can I just get a fuel pump relay from like a 1998 Camry or something and use that? Or is there some other part I need to use?

Thanks again for all the help!
 
underscore":2jk71up6 said:
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.
Just realize though that the ECU injector duration time is based on an estimated fuel pressure. When not under full-throttle, the ECU utilizes the resistor to slow the fuel pump down, which results in a lower controlled fuel pressure, and the injector duration is based upon this lower pressure. Yes, there is +/- fuel trim capability, but typically only within a +/- 25% range. If you eliminate the resistor on an ECU made to operate a resistor, you may get very rich idle condition and low speed conditions even up to highway speeds. Negative sustained fuel trim adjustment may not completely correct this. I'd be "concerned" about this aspect if purposely eliminating a fuel pump resistor on a vehicle with an ECU designed to control electronic fuel injection with one.
 

underscore

Well-known member
I noticed no change in the AFRs on my wideband when I made the switch, it has datalogging capabilities so at some point I could do the same drive with and without the relay to see if there's a noticeable difference. I'm curious just how much the flow/pressure of the pump is changed by the resistor, somebody with a fuel pressure guage should be able to compare the with/without pressure at idle to see.
 
There is a fuel rail pressure regulator on these engines too, which may help maintain fuel rail pressures in the range the ECU was programmed to control fuel injector duration. That being the case, the fuel pressure regulator may just open more at low RPMs/low engine loads to keep fuel pressure low if the fuel pump isn't allowed to run off of its resistor in these cases. So you have a good point there, Underscore.
 
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