Better Year for Seville?

[Gary Christensen CLC # 21112]

I'm starting to look for a Seville (the ones in the mid 70s) and since the model years look so similar, I'm wondering if there's a recognized "preference" technically.

Does anyone have thoughts?

Thanks.

Gary

[bcroe]

I'm starting to look for a Seville (the ones in the mid 70s) and since the model years look so similar, I'm wondering if there's a recognized "preference" technically.
Gary 

76-79 all used the 350 Olds with EFI.  77 and later have heavier wheels and
studs.  78-79 went to an aluminum intake, can corrode,  has a smaller
throttle body.  The HEI ignition used a special module attached to an
ESS unit unique to 78-79.  Bruce Roe

[Scot Minesinger]

Nice car for sure, and do not think you can really go wrong with any year, but based on what Bruce wrote 77 seems best if becomes available.

[bcroe]

Some have dropped a 76-77 HEI in with good results to solve ESS issues.  My
79 (Eldo) has a 76-77 iron intake and the big throttle body, better match to
my 79 403 engine.  I saw one in the yard with a 455.  If you find one converted
to a carb, check that the job was completely and neatly done (only ones I have
seen were done by me).  Bruce Roe

[66 Eldo]

76 was the only year with rear drum brakes. 77-9 had rear discs.
79 CA models had an O2 sensor where others didn't.

I'm partial to the 77 and 78 years mainly for the interior. Total subjective opinion but I like the seat patterns, steering wheel and woodgrain better.

[TJ Hopland]

I didn't know they had drums in 76.  Seems odd they didn't do disc from the start.

[bcroe]

I didn't know they had drums in 76.  Seems odd they didn't do disc from the start. 

I read they began from a Nova chassis; that might explain it.  Then add heavier
parts in 77.  I am not a fan of rear discs in consumer vehicles, because of the
service nightmare created by the emergency brake cable.  The 2 vehicles of the
era I have had with rear discs, were both troublesome.  So much so, I contemplated
converting them to rear drums (disc was an option).  Bruce Roe

[Gene Beaird]

Some have dropped a 76-77 HEI in with good results to solve ESS issues.  My
79 (Eldo) has a 76-77 iron intake and the big throttle body, better match to
my 79 403 engine.  I saw one in the yard with a 455.  If you find one converted
to a carb, check that the job was completely and neatly done (only ones I have
seen were done by me).  Bruce Roe

Bruce, doesn't the ESS manage the timing for the injectors?  If so, how does the computer do it with a standard HEI distributor? 

[bcroe]

Bruce, doesn't the ESS manage the timing for the injectors?  If so, how does
the computer do it with a standard HEI distributor?   

The Electronic Spark Selection works with a special HEI module, EGR signal,
and a fuel economy vacuum switch to partially control advance; this in
addition to the usual mechanical/vacuum advance.  It has no control of
injector pulses; you can see that with a careful examination of the wiring. 
Bruce Roe

[TJ Hopland]

The distributors for the EFI system looked and worked like any other HEI but had a 'pod' in the stalk that contained 2 sensors and a magnet on the shaft.  This was a batch fired system with 2 batches so 1 sensor for each batch.  Since it was just batches the timing was not super precise, it just had to be somewhat close. 

Ya other than a different internal module and the external module the ESS distributors didn't otherwise look any different.   You would presume the 'curve' could have been different knowing that it has some electronics involved.    GM also had another similar thing on some other cars from that era.   I don't think it was as fancy as the Seville version which I think did actually vary the timing.   The other system just would throw an offset at it.   I suspect it was supposed to be kinda like the early 70's where there was that speed sensor that would change the vacuum signal to the distributor for emissions.  You saw it on all those crappy downsized V8's in that 79-81 era before they got the computers working.   

[Robert Andrews]

Bruce I have a 76 with a terrible stumble problem. I am not up to speed on the ESS ?. I have been all thru the gas system
and am not getting close. Could the HEI or electrical be the problem?

[TJ Hopland]

I think the ESS was just an option on 78's.   A 76 would be a standard HEI ignition system.

Have you tried a test drive with the distributor vac line disconnected and plugged?   Like most distributors when the vacuum operates it flexes a wire or wires in this case.   Eventually the wire(s) will crack so they can be intermittent depending on the vacuum signal.  At first you can usually feather the gas pedal and keep em running but eventually they get to the point where they don't work at all.   Vac flexes the wires and looses the connection so you loose spark.  Lack of spark changes vacuum which moves it to the point it connects again so you get spark till the vacuum changes and so on. 

Disconnecting vac for a test should help narrow it down but next would be to pull the cap and rotor then unplug the green and white? connector from the module and use an ohm meter to test while flexing the wire. 

Its not an expensive part but the distributor has to be removed from the engine and pin driven out of the drive gear to replace it. 

[Robert Andrews]

Sounds like you may have a good idea. I am past thinking its the gas supply. I will try your idea. thanks

[bcroe]

The 5.7L engine only only used the ESS module/HEI in 78/79. 

If your ignition checks out, you may have a lack of fuel from the ECU.  This
could be lack of acceleration pulses, or a problem overall with the MAP
circuitry.  Try just turning on the ign and then slowly opening the throttle. 
You should hear the injectors click up to 21 times.  If that works, I'd be
suspect of the MAP circuitry which has a high failure rate.  The original MAP
is no longer available, but I have designed a drop in replacement.  The
FIRST album on my PHOTOBUCKET shows how you can check your MAP. 

     http://s93.photobucket.com/albums/L71/bcroe/

  click on an Album
  click on a picture to enlarge + description

BRUCE ROE      CLC # 14630                            bcroe@juno.com
5719 EAST SKINNER ROAD,
STILLMAN VLY, IL    61084-9215          Phone  815 234-8039

Trying another ECU from any 76-79 5.7L car is a good check.  I can test
your ECU for free, if you pay postage.  Repairs, a little more. 
good luck, Bruce Roe

[Gene Beaird]

Bob, make certain the vacuum line on the ECU hasn't come loose.  Moving the ECU around, or even just messing with stuff under the dash can pull that vacuum hose to come off.  IIRC, the engine goes full rich when that happens, but it could be the source of that stumble. 

Check the simple stuff first. 

[Glenn R. McLeod]

The best year for Sevilles was '75, '76 & early '77s. The reason being that they used big exhaust valves compared to the later ones. The way you can tell which is which on '77s, is to check the V.I.N. code. Check the 5th. digit. If it is a letter 'R', it has the big valve heads. The letter 'B' signified the small valve heads. As far as the Electronic Spark Selection (ESS) decoder is concerned, this was only fitted for emissions purposes on '78 & '79s. The way to disconnect this, is to look for one of the 2 sets of 4 wires coming out of each end of the module. One of them goes to the distributor. Select the green and black wires and short them together. This bypasses the decoder altogether. Then remove the spot-welded restrictor plate on the distributor advance diaphragm. It will then advance with vacuum only, up to the normal amount of advance that non-ESS decoder cars would use. Another reason for choosing '75s or '76s, is that they had rear drum brakes. The self-adjusting calipers of the disc brake models kept on failing. Cadillac ceased to use them on rear drive cars from 1980 and onwards, for this reason.

[Eric DeVirgilis CLC# 8621]

There is no 1975 Seville.

[35-709]

Surprised no one has mentioned the fuel injector o'rings.  These get brittle with time and leak, they were/are a major fire hazard and need to be inspected regularly and changed as a routine part of maintenance.  This from my mother's personal fire experience with her '76 back in the day and not a rare occurrence by any stretch.  My family had a Cadillac-Pontiac dealership at that time, some like the Seville --- I would not care to own one.

[TJ Hopland]

There is no 1975 Seville.

But you could buy a 76 Seville in what April or May of 75?   

[bcroe]

Surprised no one has mentioned the fuel injector o'rings.  These get brittle with time and leak, they were/are a major fire hazard and need to be inspected regularly and changed as a routine part of maintenance.  This from my mother's personal fire experience with her '76 back in the day and not a rare occurrence by any stretch.  My family had a Cadillac-Pontiac dealership at that time, some like the Seville --- I would not care to own one. 

There is plenty of maintenance that can be done on these cars to keep
them roadworthy; much is mentioned elsewhere.  Much of the Seville stuff,
including the EFI 5.7L, was transferred over to the Eldo as standard when
it was downsized in 79.  Before commuting 2000 miles to the GN and 2
other nationals in 2015, I spent 2 solid months getting my 79 Eldo
roadworthy again.  There is an 18 page description of adventures here. 
At the very minimum, take care of tires, brakes, timing chain, and the
EFI system, to avoid unrecoverable damage. 

To my taste the Seville is underpowered; it should have had a 403 instead
of a 350.  Unfortunately that engine didn't come out till 77.  But there are
ways to overcome this, without detracting anything.  Bruce Roe