# ABA OBD1 Motronic ECU/FP Relay Failures PICS



## Vanagon Nut (Oct 19, 2007)

Hi all.

Have any swappers had issues with ECU power supply or fuel pump relays failing?

My swap runs ok but now has intermittent hard starts similar to what it had before. The previous hard starts were likely caused by a dying ECU and/or FP relay (see pics of final failure). The van eventually died in my driveway (lucky me) and the fault was for sure at the ECU relay. Failures likely due to relays being poorly secured and heat at the solder joint (power draw). But.....

Any suggestions as to what other swap related issue could cause this? Or is the ECU power supply relay circuit-part, a poor design? (OBD2 uses a fuse)

The FP, ECU, HO2S relays and fuses are packed pretty tight in a VW junction box. Would heat in the box be an issue?

I securely installed 2 "weather proof" 40 Amp relays. One for ECU, one for fuel pump. They've worked fine for about 4000 miles but now I wonder if power demands are causing a similar failure within the ECU relay.

Much thanks,

Neil.

images of solder failure at 30 pin of ECU power supply relay



















New (at time of install) fuel pump relay suffered a similar fate


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## Eric D (Feb 16, 1999)

Those failures are quite common, I personally use a 70A load reduction relay in the CE2 fuse box.
I won't give you a part # since the brand I used has been discontinued for over 10 years.
A 70A 12v relay is common and easily found on-line, many retailers offer it. These are a direct replacement for the 40A load reduction relay.

VW used a 40A load reduction relay for the Mk2 and Mk3. The Mk4 had as an option a 70A load reduction relay, but it costs more than double of the aftermarket ones.

The load reduction relay won't prevent the ECU relay from cold solder joints, I use it for piece of mind.
I also upgrade my power wires to the fuse box. I make my own out of 4 ga wire, for the positive, I split it into two and use two factory red terminals.

You can easily solder your relays, add some flux and make the solder blob larger.

I also prefer to use a 120A alternator from a VR6. 
Make sure your ABA alternator is a Bosch brand, and reuse the ABA pulley on the VR6 alternator.
If you have a Valeo 90A alternator on the ABA, you can not use its pulley on a VR6 alternator. You would have to source a Bosch 90A ABA pulley.
Or ideally a 150A VR6 alternator as used in certain Eurovans and its Rialta/Winnebago cousins.
These are Bosch alternators that would require the same Bosch ABA pulley.

So you can tell I prefer to have an alternator that provides more current than I'll ever need, and have wiring that can support current voltage requirements and amperage and future ones too.
None of these upgrades are costly and it won't hurt to upgrade.


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## Vanagon Nut (Oct 19, 2007)

Thanks Eric D Good to know this type of relay failure isn't uncommon. 

The alternator pulley is stock AFAIK (c/w engine). But that's a really important point and one I hadn't considered. I'll double check that. IIRC, the alternator is 90 Amps. I would do well to upgrade (and make sure wiring gauges are sufficient). I'm running 3 batteries (starter, 2 house batteries)

The fuel pump relay most likely suffered from vibrations due to my ham handed install. They were a fairly tight fit in a box but were not secured to the box so vibration took its' toll. But the ECU relay as you can see, shows signs of heat failure too.

I do recall checking Amp draw at the ECU relay but don't recall it being super high at idle or, say, 3K RPM's. The ECU, FI's et al were drawing like 5 Amps at most? But.... 

At freeway speeds, with my gearing, the revs are likely higher than that seen in a Jetta in 5th. Thinking now, this may put a much higher draw through the ECU relay. Does that theory sound plausible? 

The only other issue I can think of right now is the + wire to CMP. Bentley notes a difference in some early '93 models. While dealing with the harness for the swap, I replaced wires to the CMP plug. As per the diagram, I may have connected the CMP ~12V + to the power supply relay output buss but I can't see how that would harm the power supply relay.

To inspect these new relays

http://www.picocanada.com/en/product/928.php

would require cracking them open. They're sealed units. But. They're not expensive.

Again, thanks for the help. The old faulty relay was most certainly the cause of a freeway stall on I5. Not something I want to have happen again!

Neil.

Engine pre swap. Test fit of AC delete setup.


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## Vanagon Nut (Oct 19, 2007)

*Relay ok it seems PIC*

Hi all.

Took apart the "sealed" Pico relay. They sealed it well!

Can't see any issue with low amp (switch, coil) side and contact shown looks super clean as it should for a low hour relay.

Pic isn't great, but you get the idea. The construction is different than the stock Power Supply relay but as with the OEM relay, it has a suppressing (resistor?) built in, which is good.

The fuel pump always primes so I don't suspect the FP relay as an issue (it is the same type as above with same hours)

Maybe my ignition switch is getting hinky.

Neil.


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