Need help with fuel pump resistor test

[blkprj80]

If you can, measure the voltage across the resistor during start, you should see it go to 0V when the relay is closed across it. Then, it should go to maybe 6 or 8 volts (I guess) when the current is flowing through the resistor once the contacts open. If your contacts are fried, it may not go to 0V, and it won't hit your pump with full voltage when the ECU asks for it. And your engine will stumble...

My bet is that the relay is bad. Resistive contacts are common with age.

 

[97 greenmonster]

Even if the relay checked out ok according to fsm?

 

[Parsnip]

Even if the relay checked out ok according to fsm?

There's the fuel pump relay and there is the circuit opening relay and that one is the one that is used to bypass the resistor. It is under the dash and labeled C8 in section G page 28 of the electrical parts location section of the FSM.

Just to be clear that you've tested them both is why I'm posting this and I hope I'm not offending anyone.

 

[97 greenmonster]

I checked fuel pump relay according to fsm and I think I switched circuit opening relay with I think the window or seatbelt one that u can swap in case it dies to see if there was difference I'll take it out and test tomorrow. Thanks for the help I'll post results tomorrow

 

[ppc]

Based upon my past experience I think your fuel pump is failing. At reduced voltage it can't pump enough fuel at the proper pressure.

I bypassed the fuel pump relay with my supercharger a year after the install I was having stumbling issues. With the bypass, around town it was fine. On a long trip when I ran the tank low it started to have problems. My theory is that with a low fuel level the pump was no longer submerged in fuel and was running hot at 12V. Filled the tank and everything was fine until the level was low again. I replaced the pump with a Supra pump but it didn't like the lower voltage at all so I run it all the time at full voltage without issue.

 

[97 greenmonster]

The fuel pump is about 3 weeks old. It's a denso I replaced my old stock one with new one for similar issues. With new pump problem went away for 400 miles and then strayed slowly coming back.

 

[ppc]

Is the Denso pump designed for dual voltage? What was wrong with the previous pump?

 

[97 greenmonster]

It's a factory replacement pump. The old one was having poor idle and would stumble and after driving for awhile. It seemed like when pump got hot it started acting up. New pump ran fine for 400 miles and slowly started acting up

 

[ppc]

What do you mean by factory replacement pump? OEM Toyota or something aftermarket like you would source from Auto Zone etc.?

 

[97 greenmonster]

As I understand the factory pump is a denso unit so that's what I bought

 

[ppc]

Denso may be for earlier models but my 94 it's an Aisan marked with "4F8"
The Toyota # is 23221-46060

 

[97 greenmonster]

Well new pump was listed for 97 and worked great for 400 miles.

 

[landcrshr]

I just tested my fuel pump resistor as per the fsm and its reading 1.7ohms when it's suppose to be .70-.76omhs.

If you can confirm that is an accurate measurement, then that is waaay out of tolerance (mine read 1.0 Ohms including 10 ft. extended meter leads). Not sure how much it actually matters, but it could potentially cause too low of voltage at the fuel pump.

You can easily test the operation of the relay/resistor circuit by probing one wire. This one, the RED/GREEN wire at the ID2 connector in the left kick panel:

Like this, this is the voltage I read (with respect to ground) while idling:

Immediately after startup, within the first two seconds, this is the reading (when the resistor is bypassed):

I hope this provides some reference.

 

[97 greenmonster]

Thanks for the pics and test I'll try it later

 

[artech]

Others with similar performance problems have found that replacing the fuel pressure regulator has solved their issues.

Just throwing it out there, hope this helps.

 

[97 greenmonster]

So I checked the voltage as described by landcrshr and I got 13 volts at start up and 8.6 at idle. I tested earlier more with fuel pump resistor jumped and couldn't get it to act up at all. For the test I did re install it. So what should be my next step. I'm going to start posting on my other thread I started first about bad idle and hesitation and claiming I'm getting ready to jump off my roof. So anymore help would be great if you could post over there maybe some when can help. Also anyone one else that had posted ideas I will get to them all and report on my results so please don't think your help has fallen on deaf ears I just have limited time to try them. Thanks

 

[maddss]

Did you ever find the problem. If so what did you replace