School me on relays

[Leo99]

My Rav still hesitates to start when it's been sitting overnight. Not the battery, not the starter. I'm going on the theory the fuel line is losing its prime overnight. I don't hear any fuel pump sounds when I turn the key on but don't start so I suspect the EFI relay might be on the fritz.

From what I read, the EFI relay sends power to the fuel pump at start up. After that, what I read said the fuel pump gets its electricity from another circuit and the EFI relay doesn't do anything. Does that sound right to you?

Looking up the replacement EFI relay, I've seen RY302 and 20382. Picked up a 20382 at Autozone. The box it came in say 20382 but the relay itself has a bunch of other numbers on it. All the relays look alike, are they different inside? I mean besides big amp side open with the small closed or big amp side closed with the small side closed. What do all the numbers mean?

 

[eljefino]

A relay turns a small current into a large current.

Computer transistors (semi-conductors) want the fuel pump to run, but would burn out powering it directly.

So it powers (usually grounds, actually) a relay's coil which is an electromagnet that closes "bigger" contacts that allow the main current to do its job.

Back in the 80s GM cars used to run the fuel pump off the oil pressure switch, except for four seconds at the start when the relay did the job. If the relay conked out you could crank the engine until it had oil pressure then it would run. Your yota could have the same deal, but, probably not.

The typical diagnosis is to see if you have power exiting the FP relay, as it could be something computer-y or anti-theft-y blocking it before you drop the tank and look for power *there* just due to convenience.

Your typical "4 pin" relay is often called a "bosch relay" and it's pretty standard with bunches of part numbers that interchange. An optional fifth pin lets power out only when *unpowered*. If toyota didn't want a bosch relay inserted, they'd alter the pinout or put a plastic blocker tab in so you had to use their spec relay.

 

[Leo99]

Thanks, I was hoping it's the oil pressure switch thing but I fear it's not. I didn't hear the fuel pump with the new relay, either.

It's a typical 4 pin relay.

 

[Wheel]

There are some standard number relays, others you need to find the data sheet for - there's a great write up here http://www.12voltplanet.co.uk/relay-guide.html

I think you may see other issues with a bad relay, like random cut-outs while running. How is the fuel pressure ?

 

[tomcat27]

do you have a fuel pressure tester? or borrow one?

 

[Leo99]

Originally Posted By: tomcat27
do you have a fuel pressure tester? or borrow one?


I'd get one but I don't see a fuel line pressure port. I'll have to pull the air box off and look for one.

 

[Leo99]

Originally Posted By: Wheel
There are some standard number relays, others you need to find the data sheet for - there's a great write up here http://www.12voltplanet.co.uk/relay-guide.html

I think you may see other issues with a bad relay, like random cut-outs while running. How is the fuel pressure ?


My wife says other than the hesitating to start, it runs great. She drives 55 miles each way to work; mostly highway speeds.

 

[Superflop]

Have your wife turn the ignition to the "on" but don't start leave it on for 10 seconds. Turn off then back to on for 10 and see if it starts immediately.

If you suspect Power loss start by checking for parasitic draw with a multimeter. Shouldn't have more than something like 40 miliamp draw with all modules at rest.

 

[Leo99]

Originally Posted By: Superflop
Have your wife turn the ignition to the "on" but don't start leave it on for 10 seconds. Turn off then back to on for 10 and see if it starts immediately.


She tried that with the old relay but it didn't help any.

 

[sleddriver]

Have you heard the FP previously when all was well? You indicated that a NEW FP relay didn't help, correct?

How cold is it this time of year in NJ? How old is your coolant temp sensor?

If it's out of spec or defective, a cold engine will be tough to start. Once warmed up though, it'll easily restart.

 

[abycat]

I know allot of people say fuel pumps usually work or don't but most of my fuel pump failures have been a slowly dieing pump. a fuel pressure test would tell you what's happening at least.

 

[clinebarger]

Originally Posted By: Leo99
Originally Posted By: tomcat27
do you have a fuel pressure tester? or borrow one?


I'd get one but I don't see a fuel line pressure port. I'll have to pull the air box off and look for one.


As a general rule, Japanese vehicles do not have fuel pressure test ports.

 

[Gokhan]

A relay is nothing but a switch controlled by voltage instead of mechanically. Why don't you just test the relay before you replace it? All you have to do is to remove the relay first and then apply 12 volts to the control terminals and see if the ohmmeter reading at the high-current terminals switch from zero to infinity or the other way around.

 

[Leo99]

Well, it wasn't the relay. The engine was harder to start this morning than it's even been. Whatever it is, it's getting worse.

It's about 55-60F in my garage overnight.

 

[supton]

Cranks normal, just no fire; or cranks but tries?

 

[LeakySeals]

It starts right up when it's warm and only turned off for a few minutes? Or is it always hard to start?

 

[Leo99]

Only hard to start in the morning. My wife gets in the morning. The engine turns over but sounds a little weak and then it fires up. She drives an hour to Dunkin Donuts, turns off engine, gets her coffee, comes back and it starts right up. No problems at lunch or driving home from work.

In the morning the first start is hard, then it starts and I can let it run 10 seconds and then turn it off and it starts back up just fine.

It sounds like a weak battery when it starts but the battery checks out fine, the headlights don't dim and it starts back up repeatedly. I'd think if the battery was weak, I'd get one start out of it and then it'd be too weak to start again.

 

[Oldmoparguy1]

Sounds to me like a failing battery. Has it been tested?

 

[Oro_O]

Originally Posted By: Oldmoparguy1
Sounds to me like a failing battery. Has it been tested?


+1. Everything indicates a failing battery. How do you know the battery is OK? What was done to physically test it?

You can test it easily w/o a trip to the store by either:

A)trying to start it in the AM after sitting with the battery in your camry in the circuit with jumpers (negative on camry to ground).

B)Alternatively switch the batteries; they should be the same (Group 24 I think in both cars).

 

[Gokhan]

I don't have much experience with fuel-injection system problems but it sounds like either the pump isn't priming and you have dry fuel lines as a result or there is some sensor that has gone bad that doesn't tell the ECM that the engine is cold. Or it could be some problem in the ECM itself. ECM is supposed to supply a lot richer mixture to the engine when it's cold.

Another possibility is that the EGR doesn't turn off when the engine is cold, which would definitely stall it.

So, it's a fuel-system, EGR, or some other emission-system problem. It's not an ignition or other engine problem because it doesn't happen with hot engine.