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fuel pump diagnosis doublecheck


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16 replies to this topic

#1 ferox

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Posted 31 May 2009 - 08:11 PM

So I have a fuel pump that is not pumping in an '84 wagon 4WD EA81 w/ Hitachi. New fuel filter and vapor separator. I was trying to get a current reading on it while the car was running, when the fuel pump stopped working. It seemed like the pump stopped running when I pulled on the wires lightly (literally very lightly), but I have biased my diagnoses too many times in the past and don't want to misread causation from coincidence.

I jumped 12v to the pump and it seems to work great.

With the key in RUN, there is 12.3 volts at the pump electrical connector by testing it with both: the meter connected to hot lead of connector and chassis ground, and meter connected to both leads of the connector.

With the engine cranking, voltage at pump drops to ~1.7 V.

I hooked up my Miti-vac to the line from the tank to the pump and fuel poured freely before any vacuum.

Before the car died, I had hooked up the Miti-vac to the fuel supply line in the engine compartment and was able to pull fuel through no problem.

I checked all the fuses in the fuse box under the dash.

So the pump is getting power, and the lines aren't clogged, so it would seem that the pump is bad even though it seems to run fine when jumped directly to a 12v source.

I don't know where the relay is or if there are any other fuses, so I have not checked those. Could the pump be getting full voltage, but minimal current? I just wanted to double check with you all to see if I am missing something before replacing the pump.

#2 4x4_Welder

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Posted 31 May 2009 - 08:21 PM

A poor connection will still show full voltage on a meter, but as soon as there is a load on the circuit, like plugging the pump back in, the resistance shows itself. If you were to check voltage while the pump was plugged in, then it would be very low.
I don't think your car runs the fuel pump while cranking, just while running.

#3 GeneralDisorder

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Posted 31 May 2009 - 08:28 PM

Could the pump be getting full voltage, but minimal current?


Yes - that could easily be the case. If the wiring is damaged it may not be able to carry the load of the pump.

The fuel pump control unit is designed to run the pump for about 1.5 seconds when the key is placed into the run position. Then it runs it continuously if you are cranking or the engine is running (whenever a tach signal is present from the coil).

GD

#4 ferox

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Posted 01 June 2009 - 12:54 AM

A poor connection will still show full voltage on a meter, but as soon as there is a load on the circuit, like plugging the pump back in, the resistance shows itself. If you were to check voltage while the pump was plugged in, then it would be very low.

Thanks guys

The voltage dropped to 4.06 V with the pump connected.

So it sounds like I have either corroded connections at the FPCU, bad connections inside the FPCU, or the most likely candidate...failed wiring. Does that sum it up, or am I missing another possibility?

And is the FPCU behind the driver's side trim panel (steering column) on an '84 wagon?

#5 '84 Flat-Four

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Posted 01 June 2009 - 09:04 AM

your FPCU should be mounted with the bracket that holds your hood-release cable/handle. It's a black box, and I'm not so sure you can open them up to troubleshoot it (not 100% on this)

When mine went, I got lucky at the JY and haven't had any issues since. Incidentally, mine "went" because of a windshield leak. The water corroded all the connections, fried my ECM, and my FPCU.

With the new one (new to me) I mounted it with a ziplock bag overtop of it, until I fixed the leak.

#6 GeneralDisorder

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Posted 01 June 2009 - 06:39 PM

[quote name=''84 Flat-Four;827651]your FPCU should be mounted with the bracket that holds your hood-release cable/handle. It's a black box' date=' and I'm not so sure you can open them up to troubleshoot it (not 100% on this)[/quote']

They also come in blue on the feedback carb models. They are solid-state and yes you can open them easily with a screwdriver. Testing them is relatively easy once you figure out the pin-out. I recently used a blue one from an EA81 feedback vehicle to power the electric fuel pump for a Turbo Suzuki Samurai build (Samurai's have mechanical fuel pumps stock) - you give them a tach signal, switched 12v, ground, and the fuel pump power or ground (I can't remember which just at the moment). The black units have additional pins for powering the electric choke.

GD

#7 ferox

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Posted 01 June 2009 - 11:18 PM

Thanks for the info., very helpful. I pulled the FPCU, took it apart and found a fairly burnt component. I don't know what it is, but I smells and looks burnt. I have a hunch this is from the overcharging condition that has been going on in the car for a while now. I jumped the pump from the battery through the FPCU connector and the pump immediately started pumping fuel, so I think I have located the problem...with your help, thanks again.

I think I know the answer to this one, but would an FPCU from a carbed ea82 work as a replacement? EA81's aren't as plentiful in the yards as they used to be (hopefully that's because more people are hanging on to them and fixing them up).


The pic's don't quite show the magnitude of the apparent damage, but you get the idea.
Posted Image

Posted Image

#8 ferox

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Posted 02 June 2009 - 11:01 PM

Bump to see if a carbed ea82 FPCU will work.

LKQ says they have two '81's at Foster and an '80 at Tigard, which are externally regulated alternator models. Will those work?

Dealer says $165

#9 GeneralDisorder

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Posted 03 June 2009 - 08:39 AM

Bump to see if a carbed ea82 FPCU will work.

LKQ says they have two '81's at Foster and an '80 at Tigard, which are externally regulated alternator models. Will those work?


I beleive they will not. But check to make sure. I haven't owned an externally regulated rig in a long time.

As long as the EA82 has a non-feedback carb it will have some kind of FPCU that works on the same principle. The EA82 feedback's don't have one as the ECU controls the fuel pump. Look for a non-feedback - it should have one somewhere - not sure it will be in the same place. The only carbed EA82's I've had were both feedback so I haven't looked for one before.

GD

#10 4x4_Welder

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Posted 03 June 2009 - 11:34 AM

If all else fails, you could probably replace that transistor and if the circuit traces on the other side are bad, jumper them with small wires. I've done that before to repair cracked circuit boards.

#11 ferox

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Posted 03 June 2009 - 09:04 PM

I beleive they will not.

That's what I was thinking. The wiring on the 80-81's is quite a bit different than later models. Seems like an ea82 FPCU would be more similar the one in the '84 ea81. My wife has been taking my car to night classes, so I haven't had a chance to directly compare the unit in my '81.

If anything, I might be able to find the same transistor in one of those units to swap into the damaged one. The connections on the back side of the component board were in decent shape, so it's appears to be salvagable.

Thanks again

#12 GeneralDisorder

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Posted 03 June 2009 - 09:12 PM

If anything, I might be able to find the same transistor in one of those units to swap into the damaged one. The connections on the back side of the component board were in decent shape, so it's appears to be salvagable.

Thanks again


Other components could be damaged without being actually burnt looking. There's a chance that replacing it will fix the problem, but there's also a chance it will not. There's also a slim possibility that what caused the transistor to blow in the first place is another component on the board being out of spec..... which will just keep eating them.

If it were me I would find another one from a yard around here - there's plenty of yards to choose from - remember that calling them isn't always going to work since EA81 hatchback's were made till '89. I'll look though my junk and see if I have another one - you need the black one correct?

GD

#13 ferox

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Posted 04 June 2009 - 10:37 PM

Other components could be damaged without being actually burnt looking. There's a chance that replacing it will fix the problem, but there's also a chance it will not. There's also a slim possibility that what caused the transistor to blow in the first place is another component on the board being out of spec..... which will just keep eating them.

Yeah I thought of that, then I thought about what I would have to do to check the individual components, and then I thought $165 for a new one would be better than that option.

If it were me I would find another one from a yard around here - there's plenty of yards to choose from - remember that calling them isn't always going to work since EA81 hatchback's were made till '89.

Yes, I wish it were more reliable to call, but I go even if they say they don't have any. I don't want to sound racist, but sometimes the person that answers the phone doesn't understand my english very well. I am also curious to find out the similarities of the ea81 & ea82 FPCU's. Incidentally, I also need parts for my Jeep, so I will be hitting the Damascus and Foster yards at the very least.

I'll look though my junk and see if I have another one - you need the black one correct?

Thanks GD, that's awfully nice of you. Don't put yourself out, I am going the post what I find out about the various FPCU's after my yard runs. And yes the black one.

#14 ferox

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Posted 09 June 2009 - 12:20 AM

Following up...they crushed the two '81's on Friday, and I could not locate a component in the ea82's that looked quite right, so I ended up with a FPCU out of an '82 that was also fried in the same spot. For now, I have direct wired the pump through the FPCU connector with a fused switch.

After seeing Subydooder's (sp?) replacement component for the same problem I think I will try to repair the FPCUs and continue looking for one that is in better condition.

#15 Cougar

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Posted 09 June 2009 - 09:43 AM

You may be able to fix the board by just replacing the output transistor though other things could be bad also. The cross reference for that part is a NTE 55. Here is a link for you to see.

http://www.nteinc.co...9/pdf/nte54.pdf

#16 stickedy

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Posted 09 June 2009 - 09:52 AM

If I were you, I would change that Transistor. Cost should be around 1 $ I guess (without checking it, but thise things are standard parts with no real costs) and it's made quite fast. And checking if it's working again then is also a quick task. Worth a try and think about all the money xou can save ;)

#17 ferox

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Posted 09 June 2009 - 08:38 PM

Thanks, I will definitely be replacing the transistors and checking to seeing if they get hot...as Subydooder described in his concurrent thread. And if so, I will switch out the fuel pump as well.

This has been a pain and an inconvenience, but it is good to learn more about the circuit and know how to by-pass the FPCU in the event that it doesn't die in front of my shop next time. Not that there will be a next time...who am I kidding.

Thanks to all for the help!




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