A9L Main Board Capacitor Issue

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A9L Main Board Capacitor Issue

Postby cwtoyota » Thu Feb 18, 2010 8:51 am

I have a bad capacitor on my A9L board in my daily driven Toyota Pickup. One of the legs of the capacitor appears to be either burnt or corroded and is broken. Obviously I need to replace this capacitor, but I would like to know what this capacitor is for and what could have caused it to burn out a leg.

I'm going to guess it is either related to TFI/Ignition or the HEGO sensor system.

I also have a pretty good miss at high load and high rpm. The miss may be related to TFI wiring/issues/mysteries.

Please reference the picture of my board below. The red arrow points to the 47mf 16v capacitor.

Image
•1989 Toyota Pickup X-Cab 2x4 [1995 5.0L H.O. (A9L & M12071-C302)]
•Moates F3 / F2A / F2E
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Re: A9L Main Board Capacitor Issue

Postby Chucko » Thu Feb 18, 2010 10:37 am

That is almost certainly a power supply bypass capacitor. Its failure means there's more electrical noise on the power supply lines of the board. This could cause all sorts of unpredictable behavior - possibly including no change.

Electrolytics usually die by drying out or leaking their guts out over the years.

I doubt the value is critical. A bigger valued replacement would be fine. I would replace all the other electrolytic caps of the same value at once. I see at least two more in your photo.
'89 LX 5.0, Crane 2040, Pro-M 80 mm, 65 mm TB, ported stock intake & E7TE heads, 24 lb injs., JBA shortys, cat X-pipe, A3M1 (GUFB strategy) w/Moates Quarterhorse, BE & EA, close ratio T5Z, 3.55 rear
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Re: A9L Main Board Capacitor Issue

Postby Chucko » Thu Feb 18, 2010 10:40 am

Regarding your miss... is your TFI module original Motorcraft or a 3rd party replacement? I replaced my original with a cheap 3rd party part and suddenly had major misfire at high load in the power band. Replacing it with another Motorcraft part fixed this. I now carry a spare Motorcraft TFI in my car at all times.
'89 LX 5.0, Crane 2040, Pro-M 80 mm, 65 mm TB, ported stock intake & E7TE heads, 24 lb injs., JBA shortys, cat X-pipe, A3M1 (GUFB strategy) w/Moates Quarterhorse, BE & EA, close ratio T5Z, 3.55 rear
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Re: A9L Main Board Capacitor Issue

Postby cwtoyota » Thu Feb 18, 2010 10:52 am

I'll just replace all three 47 mf caps while I have the board out.

The miss may be unrelated, or the noise in the circuit may be causing it. I have an odd combo:

The engine is a 1995 Mustang GT 5.0L with a 1990 modified injector harness.
I'm running a brand new M12071-C302.
I'm using the 1995 distributor (remote mount TFI) with a factory TFI on a heat sink.
I had to create a special adapter harness to go from the round 8 pin black plug on the dizzy to the '90/'93 TFI harness.

sometimes the miss doesn't show up at all, other times it's bad... I've used other TFI modules. This TFI module/engine runs great with the T4M0 board. I wish I had another A9L to try... I don't want to re-pin my 60 pin plug just to verify this is an ECU issue... I guess I'll find out when I replace that bad cap.

I'm using the 1995 70mm MAF too (changed to the 70mm T4M0 MAF transfer function on my Moats chip).
•1989 Toyota Pickup X-Cab 2x4 [1995 5.0L H.O. (A9L & M12071-C302)]
•Moates F3 / F2A / F2E
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Re: A9L Main Board Capacitor Issue

Postby cwtoyota » Fri Feb 19, 2010 1:37 am

Ok, replaced the caps with some of equal value today after work.

Went up the street on a test run, same miss/stumble issue.
Definately feels TFI related... You ever just have that gut feeling?

Anyway, pulled off to the side of the road, shut down and checked out the TFI harness and connectors. I tweaked the tabs a little in the TFI module so they have some memory pressure when I plug in the harness.

Now it runs smooth as silk. You wouldn't think there would be an issue like that on an install of a brand new harness (purchased in October / installed in November) so soon. There's still silicon dielectric spray in there too. Chock that down to Fords low quality electrical connectors.

Lessons Learned:
-Check your connectors FIRST!
•1989 Toyota Pickup X-Cab 2x4 [1995 5.0L H.O. (A9L & M12071-C302)]
•Moates F3 / F2A / F2E
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Re: A9L Main Board Capacitor Issue

Postby Chucko » Fri Feb 19, 2010 12:14 pm

cwtoyota wrote:Lessons Learned:
-Check your connectors FIRST!


Good advice. It's always the simple little things that bite me, like minor leaks and loose connectors.
'89 LX 5.0, Crane 2040, Pro-M 80 mm, 65 mm TB, ported stock intake & E7TE heads, 24 lb injs., JBA shortys, cat X-pipe, A3M1 (GUFB strategy) w/Moates Quarterhorse, BE & EA, close ratio T5Z, 3.55 rear
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Re: A9L Main Board Capacitor Issue

Postby BobCat » Fri Feb 26, 2010 10:33 pm

Check to see if you can still pull codes....most of the time when I find Caps burned up it is due to not running the correct O2 sensor harness for the processor.

I keep a bunch of them on hand if you can't find them send me a PM.
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Re: A9L Main Board Capacitor Issue

Postby decipha » Sat Feb 27, 2010 9:45 pm

WOW i changed out that same cap on a friends ecu about a year ago, it was in his 89 5.0, IIRC it was effecting his o2 sensors, they were crap anyways, but IIRC after replacing that cap they read differently although they were still bad
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