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79 Seville Melted Control Board

Started by Bronco_Bustin, February 11, 2017, 05:03:10 PM

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Bronco_Bustin

1979 Seville gas engine. Won't start after replacing temp sensors.

When I turn ignition on before cranking can hear all the injectors firing rapidly and continuously. The injectors stop pulsing with any throttle input.

I emailed Bruce and he gave me the wiring schematic to trace and I stumbled upon this...

What is it? Can I test it?
One of the wire looms goes to the distributor.

bcroe

That module is an Electronic Spark Selector which helps control spark advance.  The
79 Eldo and 78-79 Seville use the ESS with a special module in the HEI.  The EFI is
independent, no spark control.  ESS sometimes melts, get another one.  I suppose
a 79 Eldo has a different part number, but only for lead length; same engine. 

Another solution is just drop in a 76-77 Seville HEI which doesn't need an ESS; I
may do that myself some day.  I don't have any internal info on ESS modules as
they are potted.  Any bad ones sent here would encourage me to try and finish
melting off the goop and trace the circuit.  Then try to build a replacement.  That
still doesn't solve the problem of the special HEI module, but they seem more
reliable.  I never tried converting a 78-79 HEI to a standard module with no ESS,
the advance curve might be wrong.  More research.....

Has your ECU been checked yet?  Random injector pulses might be caused by a
bad adjustment of the Throttle Position Switch; I'd unplug it and see if the injectors
stop pulsing.  Bruce Roe

Bronco_Bustin

Hi Bruce, the first thing I did was unplug throttle position switch and yes the injector pulses do stop. I haven't tested the ECU, I was just checking all the connectors and grounds and found this melted guy...


Bronco_Bustin

So a 79 eldorado showed up at a local junk yard so I pulled the ecu and the spark selector (which was also melted).

The eldo Ecu looks like it had already been replaced. It didn't have the usual sticker identifying what it came out of, just a sticker from the company that tested it.

My Seville is a Cali car FYI so I don't know how much that will affect...

Anyways I plugged in the new ecu and it fixed the injectors clicking and started up pretty quickly. It started with high idle so I put the shims back in the cold start bypass and after it warmed up the idle was low and I couldn't raise the rpm's above 640 with the throttle body screw.

Considering that was pretty close to target I tried to drive it and it hesitates real bad at low rpm's but mid and high range runs like a rocket.

Any idea what to look for? I'm beating my head against the wall.

EGR seems to function fine and all the vacuum lines seem intact, including the distributor advance so timing is good.

bcroe

#4
It seems you have 2 ECUs, which do not run the same.  I'd say ship the worst
one here and get it fixed.  And get my fuel pump relay kit to protect the the ECU;
I just spent all morning repairing an ECU that had burned up connector and
circuit board because no relay was installed.  In the ideal final situation you would
be running a good ECU with a good spare. 

Recently I put a bad ESS in the oven to melt the goop off (when SHE wasn't home). 
The thought was to find out more about the circuit, maybe duplicate it.  However I
found a couple custom made integrated circuits that I can't buy.  And its hard to
develop a work around when a good circuit is potted. 

HOWEVER, I have a couple ESS units somebody checked in their car for me,
available.  One thing you CAN check is the voltage of your ECU MAP sensor, as
shown on my PHOTOBUCKET.  These fail a lot, original unavailable, but I have
developed a drop in replacement that is running several dozen ECUs now. 

A California ECU may be equipped for an OX sensor.  this function just about
never works any more, and can't be repaired, because the custom micro and
software it uses (8740) are not available.  But I can wire these to run as an
open loop ECU (just like all the others), no OX sensor. 

161 5883, 161 6209 and 161 9550 are closed loop ECUs.  Bruce Roe

Bronco_Bustin

Should we assume a melted ESS is a bad part? Or Is it possible that the potting just breaks down?

T.Skytte

Hi,

My 79 Eldo also has melted goo coming out of the ESS.   :o
However, the engine doesn't seem to have any issues really, maybe some hesitation at low revs but I am not sure. The fast-idle switch doesn't seem to work but that's not related I guess.

So either the ESS is still functioning, or the engine can drive ok anyway without the ESS?

@Bruce  did you say you have an ESS forsale for an Eldo? In that case what's it going to set me back and would you ship to Europe?

Best regards,
TS
----------------------------
1979 Eldorado Biarritz

bcroe

Your ignition signal goes through the ESS, so failure could be serious.  There is no
development here on the ESS, so I can only test them in the car; not very complete. 
Melting goop must mean an overheating part in the circuit, which hints at imminent
failure of some kind.  My backup plan is to have a 76-77 Seville HEI ready with no
ESS. 

Perhaps a standard 4 pin HEI module could be adapted to the ESS type HEI.  The
wiring would have to change, and perhaps the advance mechanism as well, not
investigated at this point. 

My ESSs are for sale, I ship such stuff to Europe.  Have seen them on Eb*y.  I'll
have to do a bit of research to see which car mine came out of, or if they are all
the same.  Email me   bcroe@juno.com           Bruce Roe

Bronco_Bustin

LOL maybe I should park it on the capitol lawn in Sacramento...

bcroe

Long ago mine did much better than my carb cars, same engine, same year.  I
replaced that orig cat with a new monolithic, made sure the air pump was OK. 
But that stuff is JUST ONE reason I now live in the Wild West instead of a state
by an ocean.  Bruce Roe