1970s 1976 Cadillac 500 fuel injection

[MultipleCaddies]

Hi all.. new to the forum, but far from new to the Cadillac world. I type a lot, so bear with me. I've had a few Cadillacs come and go over the years, including '61 and '70 convertibles as well as a '75 Fleetwood limo, and currently have a '72 Sedan deVille, and this '76 Coupe deVille I just picked up.

I am new to the world of Cadillac fuel injection, however. This EFI 500 is new to me, and this is a car that sat for a number of years and needs a bit of help to get it going. My first step is researching this system to fully understand it and all of its key parts before I dig into it. I'm very familiar with modern computer controlled EFI systems, but this is a little different. First question: Will the factory shop manual have in depth technical info on the system, or is there a better source out there?

Next question.. in the real world we live in today where things often go quite differently than the engineers intended, is this EFI system going to be a constant pain to keep it running right? Will it be reliable? I plan to use this car for long road trips, and the very last thing I want is to have regular breakdowns that are essentially unfixable on the side of the road due to zero parts availability. My inclination is to install a correct intake/carb/distributor/mechanical fuel pump on it and know that it will be reliable, consistent and run very well. I know there is an enthusiast base for these EFI systems, but it will quickly lose its charm to me if I have to spend a lot to get it sorted out and routinely have to fix it or have issues. It's not the fact that it is EFI that scares me, it's the fact that it is old, early EFI made before the OEMs really sorted EFI out well, combined with limited parts availability. Many early innovations started off as fine ideas, but took years or decades to really sort out well. I'd like to find out the real truth behind these systems and running one today.

I appreciate any input you all have, especially real world experiences of owning one of these and driving it regularly. I plan to put some real miles on this car, as I use my all my cars as they were intended, they don't just sit around the garage looking pretty. This is an 82k mile car that is a little rough around the edges, but is well worth saving, and I intend on making sure it stays on the road for many, many more years to come!

[TJ Hopland]

You have come to the right place.   We have one member that knows these inside out and test and repairs the ecus.  We also have a couple other members that are making some of the no longer available parts for them.  I'm sure they will be along soon to offer help and advise.

As to how big of a pain it is I can't answer that, I have been around them but never really lived with one long term.   Its a very rare these days system for the 500 but the same system was standard equipment on the 76-79 Seville so there were a bunch of them on the roads at one time.  The only other engine you could get on those Sevilles was the diesel in 78-79.   79 Eldos and CA 80 Eldo and Seville could have had em too so they were not as rare as one may think.  Today?  I'm not real sure, obviously a majority of those cars no longer exist. 

One question you have to ask when considering a carb and related systems is how many people are really good at working on those and what quality parts are available for those?  Not many people can or want to work on an old car anymore and the parts we can get today are often garbage.   

[bcroe]

For maintaining 70s Cad EFI cars I highly recommend having the blue &
white book: CADILLAC ELECTRONIC FUEL INJECTION DIAGNOSIS
Manual 1099984 / S-1453. Its usually available on EBay, currently eBay
item number: 165136935730 and others.  Get a paper book, not a CD.

In order to properly service that car, you should have at least the 1976
CADILLAC SHOP MANUAL, Cat No. S-1152.

I have driven one of those systems for a quarter century. 
For more info, or getting an ECU repaired, email me at
bcroe@juno.com

That EFI was state-of-the-art when designed, one of the
first using Integrated Circuits in an analog processor. 
But the single IC 8 bit microprocessor was invented in
1972, so analog was completely obsolete when 80 models
came out with digital EFI.  Bruce Roe  CLC #14630

[MultipleCaddies]

You have come to the right place.   We have one member that knows these inside out and test and repairs the ecus.  We also have a couple other members that are making some of the no longer available parts for them.  I'm sure they will be along soon to offer help and advise.

As to how big of a pain it is I can't answer that, I have been around them but never really lived with one long term.   Its a very rare these days system for the 500 but the same system was standard equipment on the 76-79 Seville so there were a bunch of them on the roads at one time.  The only other engine you could get on those Sevilles was the diesel in 78-79.   79 Eldos and CA 80 Eldo and Seville could have had em too so they were not as rare as one may think.  Today?  I'm not real sure, obviously a majority of those cars no longer exist. 

One question you have to ask when considering a carb and related systems is how many people are really good at working on those and what quality parts are available for those?  Not many people can or want to work on an old car anymore and the parts we can get today are often garbage.   

Thanks.. I restore classic American cars for a living and for my enjoyment, and have a particularly keen understanding of carburetors, distributors and tuning them properly. I've built many carburetors, including more than a few Quadrajets, so getting a carb/distributor setup on this engine right will be no challenge whatsoever. It will run great and be rock solid reliable, hence my inclination to go that direction. There are enough parts available for Quadrajets where that is no concern whatsoever, especially metering rods, jets and springs, so tuning is no issue, and if I go carb I would ditch the HEI distributor and run a Pertronix billet distributor. Very easy to perfect the advance curve, adjustable vacuum advance, rock solid reliable, readily available. Have installed many dozens of them in customer's cars as well as my own, and have yet to see one have any kind of failure. I have seen many HEI ignition module failures over the years, and shy away from them if at all possible. Not to mention, finding the advance weights and springs to dial them in is no easy task any more.

[MultipleCaddies]

For maintaining 70s Cad EFI cars I highly recommend having the blue &
white book: CADILLAC ELECTRONIC FUEL INJECTION DIAGNOSIS
Manual 1099984 / S-1453. Its usually available on EBay, currently eBay
item number: 165136935730 and others.  Get a paper book, not a CD.

In order to properly service that car, you should have at least the 1976
CADILLAC SHOP MANUAL, Cat No. S-1152.

I have driven one of those systems for a quarter century. 
For more info, or getting an ECU repaired, email me at
bcroe@juno.com

That EFI was state-of-the-art when designed, one of the
first using Integrated Circuits in an analog processor. 
But the single IC 8 bit microprocessor was invented in
1972, so analog was completely obsolete when 80 models
came out with digital EFI.  Bruce Roe  CLC #14630

Thanks, I'll look into getting both. I too prefer actual manuals, not CDs or online manuals.

If I'm going to keep this car running on the factory fuel injection, I'm going to not only want to freshen up all the key parts that I have now, but will need spares as well. Do you have any spare ECUs for sale? What about sourcing the fuel pumps? I believe I found a source for the in-tank pump, but not the high pressure inline pump. Any ideas?

[V63]

I have had several of these systems over the years, with Mercedes and Cadillacs. I do appreciate them, fully restored and  maintained them.

That said, your system sounds significantly neglected. I am in  a similar situation with 2 VINTAGE Bosch EFI and knowing what I know now...

 I believe I will 'start over' with a modern EFI and save myself. I have converted  a 500 (carbureted version).

[MultipleCaddies]

I have had several of these systems over the years, with Mercedes and Cadillacs. I do appreciate them, fully restored and  maintained them.

That said, your system sounds significantly neglected. I am in  a similar situation with 2 VINTAGE Bosch EFI and knowing what I know now...

 I believe I will 'start over' with a modern EFI and save myself. I have converted  a 500 (carbureted version).

I thought about adapting a modern ECU, TPS, O2sensor, etc. to this system, retaining mainly the intake, injectors and fuel rails.. but for what benefit? Modern EFI does offer some benefits over carb, but when comparing to a well-sorted carb setup the difference is not monumental. This won't be an all-weather car for me - it won't see deep freeze or 100+ degree weather, so the benefits of EFI over carb become less pronounced.

A modern sequential EFI system may offer a slight fuel economy benefit over batch fire injection.. but I can't see it being much.

I know it sounds like I've made my decision to just go carb.. I haven't. I'm open to the idea of retaining the factory EFI, if the reasons are compelling to do so.

[V63]

In general, I'm kinda 'done' with carbs unless it's a 6 volt car.

The early Bosch EFI system has tried many a car guys patience and that was when you could find the parts readily. It is best to consider it most challenging at this point in time,  especially with blended fuels.

It would take someone with most determination to find satisfaction above the frustrations.

[Chopper1942]

I have a 79 El Dorado EFI that has 215k miles on it. The only EFI parts I have replace are the fast idle valve, injector o-rings, and the in-tank low pressure fuel pump. The o-ring seals started to leak fuel and were hard as rocks. The in-tank fuel pump did not fail, car quit running and had no fuel pressure. When I removed the fuel tank and fuel sender, I found the hose between the pump and sender line had split. It runs great, passed its last emission test in AZ (have since moved). and gets great mileage for a 70's car.

[TJ Hopland]

I would say don't give up yet.  Play with the system a bit so you understand it then decide if you want to keep it. If you decide not to I would guess you could sell it for parts to someone that is trying to keep one going.  The Seville's used an Olds engine so the Cad engine specific parts are much less common and often times people 'getting rid' of the systems damaged things removing them so they were not even able to keep other systems alive.

I have run and am still running an aftermarket EFI and I would say given your experience with carbs and not intending to run in any extreme conditions I would agree its probably not worth the trouble.  Most people don't have the experience or access to people that can work on carbs anymore so it doesn't matter which direction they go its going to be a hard road either way.     

[TJ Hopland]

Oh and being a RWD car you should have the option to go with something like the Edelbrock intake if you wanted to.   In the FWD Eldo's the engine sits up much higher so you can run into hood clearance issues. 

[MultipleCaddies]

Thanks guys.. I actually have a spare factory intake and Quadrajet sitting around, so it's an easy swap.

I should have provided some more background.. this is a car that I believe was parked in the late '90s and sat for more than two decades. The seller says his mobile mechanic tried to get it fired up a year or so ago, but did nothing more than put a battery in it and crank it over with nasty old oil. He said it would only run when he dribbled fuel into the intake. Needless to say, this guy does not sound confidence inspiring. But he *says* the fuel pumps did not come on, so who knows.

The fuel tank is absolutely full of NASTY smelling varnish, so I'm obviously going to drain it out and clean it, but I'm concerned about the rest of the system as well, particularly the injectors. If they're badly varnished as well, they would need serious cleaning or replacement.

Here's another question: Does this EFI system add any appreciable value to these cars? If I remove it I would not simply throw any of it away. I would either save it all and put it on a shelf, or sell it if someone wants it. What are these parts worth to sell if I were to go that route? I have everything, including the gold lid air cleaner.

[V63]

It sounds a major overhaul of the system and you would lucky if you can save the fuel tank. The fuel pumps are probably toast. Possibly computer related fuel pump service circuit that can be done by specialist Bruice on this forum.  The 8 injectors would need to be each (at a minimum) need to be cleaned and test sprayed . There used to be serviced that did that but they seem to have vanished.

The systems are rare but more rare are those that are determined enough to tackle them (at this time). So it's supply and demand as to value. I have a few used systems myself. And at least one more coming up.

I am only trying to be 'realistic' in my advice, but if you elect to restore the original EFI that's admirable and appreciated  as well!
 

[bcroe]

If I'm going to keep this car running on the factory fuel injection, I'm going to not only want to freshen up all the key parts that I have now, but will need spares as well. Do you have any spare ECUs for sale? What about sourcing the fuel pumps? I believe I found a source for the in-tank pump, but not the high pressure inline pump. Any ideas?

Getting an old car roadworthy again is a big project, here it includes
tires, timing chain set, and total rebuild of the brake system.  All pipes
running front to back need attention, here in the rust belt that means
replacement of exhaust, fuel, and brake lines.  That 76 has the additional
electronics of the EFI system.  The ignition is not tied into the EFI. 

Learning another system is another challenge, at least there are books
fully explaining the 70s Cad EFI.  Judging from a couple hundred ECUs
repaired here this century, close to half went on 75/76 500 engines, about
as many on the Olds small block cars, and a few on 77/79 425 engines. 
Apart from mechanical engine requirements, these are all nearly identical
externally, with internal ECU variations for the ap.  Drawings for the ECU
wiring, and some sub systems, are available. 

Over the years, some EFI failures dominated, esp with the fuel pump
control.  Simple fixes have been worked out and are easily retro fitted
when the ECU is checked out.  Some part problems have been solved
with new (and IMPROVED) replacements.  Old electronics can fail,
even on the shelf.  It is good to carry a spare ECU if you can find one,
the demand has driven the 500 ECU market price up to 4 figures.  I have
a couple 500 ECUs with some updates for about half that price. 
Fortunately original ECUs are not costly to repair.  Note most 70s ECU
sources do not have means or parts to actually test or repair them. 

To restore the EFI you will need to go thru the entire fuel system,
from the injectors all the way back to the pump inside the tank. 
The hoses and injector seal will see up to 40psi, any not replaced by
this time are a fire hazard, if not already leaking.  If you decide to use a
carb, you will still need to go thru that system, changing out the intake
manifold, fuel lines including a mechanical pump, and the tank unit.
The original HEI will work fine, its extra SPEED SENSOR outouts can
be ignored.  I like HEI because anyone can service them, they do not
get wetted down and missing like smaller caps, parts are cheap if you
did not find enough in the junk yard, and the whole system is just one
component.  Modules can fail, I carry a spare that is easily replaced on
the road, no re timing required. 

It is possible to use the original 76 port injection system to convert to
sequential injection.  But that requires a new ECM to be dialed in,
new temp sensors, a new throttle position sensor, and a new wiring
harness to convert from high side bank drive to low side individual
injector drive, and another pump control.  I actually did this on my 79,
using an original speed sensor as the cam sensor.  But the ECM chosen
was not capable of properly driving the original peak and hold injectors. 
Before I solved this problem, I relocated and that system is still in a box.

If you do change out the HEI and EFI, there are other owners who
could use the spare parts. You would be removing the intake with its
injectors, throttle body, and temp sensors, and fuel rail, HEI, fuel filter
mounted where the mechanical pump goes, wiring harness to the ECU,
the ECU, frame fuel pump, and tank unit.  good luck, Bruce Roe

[MultipleCaddies]

Yikes! All this is adding up to mean I'm very likely just going to go carbureted. I just don't see enough benefit in spending significantly more to get the EFI sorted out, and still be a somewhat unreliable system. Also, being batch fire injection with a simple TPS that appears more to be a switch than a variable resistor, along with no ignition timing control, I don't see this system having the refinement or fuel economy advantage like modern systems do. I have a hard time believing it would run much, if any better than a well sorted carburetor.

Getting all of the other bits on this car sorted out is easy stuff.. I have resurrected many a classic car that was parked for decades, and am well familiar with everything else it will need. I already made a big parts order to cover most of the other long-neglected maintenance items it will need at a minimum. Once I really dig in I know I will find even more. This is one part of the process I really enjoy, in fact. And frankly it's pretty easy stuff. Seals, gaskets, hoses, belts, fluids, brake hydraulics, etc. are all easy stuff on these cars. No sweat. It would be quite different if I had to trust some knucklehead inexperienced shop to do it all, and pay dearly for the privilege.. but that's no concern for me. Plus, this is a totally unmolested original car that hasn't been hacked up by idiots, so I only need to fix what time and usage has worn out, not the mistakes of others.

More than likely, once I verify that the engine and trans are good they will come out for a full reseal of both. I'll swap the intake and everything else, freshen up the engine bay, make whatever changes I need to the fuel tank, pickup and lines, and be back on my way.

Up here in the dry desert environment of northern Nevada we don't have the midwest and east coast rust issues some of you guys suffer with. This car has very obviously not seen much if any snow season driving, it is very solid underneath. The hard fuel and brake lines are in excellent shape, and the fuel tank will probably be fine as well, based on my experience here. And if not, time for another one. That's not something I'm particularly concerned about, they're not difficult to find.

So the next question is.. would anyone here be interested in buying all of the EFI parts off of this car if I decide to take it all off and sell it? I would not want to sell the system in pieces, but as a complete system, including fuel lines, pumps and everything.

[MultipleCaddies]

The other option - that I am NOT leaning towards - is converting to a modern EFI system using only the intake, injectors and fuel rails from the original system. Something like a Holley HP with an appropriate MSD distributor for proper timing control as well, and a modern TPS and O2 sensor, among other things. Then I'm sure I could realize the refinement benefit of real modern EFI, with real tune-ability. But now we're talking $3,000+ just for parts, plus a LOT of time getting it sorted out. Again, I just don't see the benefit.

[bcroe]

I think the cheapest route is fix what you have, next is convert to a
carb, most expensive and setup time consuming is adapt some other
EFI system.  That 76 HEI ignition is exactly the same for a carb or EFI. 
Yes 76 EFI uses a clever switch for throttle position changes, probably
the most reliable part of the system and more reliable than that cheap
pot later used. 

I see the 70s system as an attempt to meet current and future emissions
requirements, mine was certainly much better than my same engine cars
with a carb.  Ignition timing is very important, needs a digital system to
build a 3 dimensional timing map and add other inputs (like temp), instead
a pair of 2 dimensional curves from the rpm and vacuum. 

The trans must come completely apart to change out hardening seals on
the clutch pistons. The chain cover is best glued back on to avoid leaks. 
good luck, Bruce Roe

[Pghcc2006]

Can someone explain to me why the carbed cars were rated at 190 horsepower and 360 lb ft torque while the EFI ones were rated at 215 and 400 respectively? It seems like a huge jump in power just for a change in fuel delivery

[V63]

simple answer : better Fuel management!

[MultipleCaddies]

simple answer : better Fuel management!

That seems unlikely, since many different Quadrajet-equipped engines made close to 400hp, and the '70 500 in particular was rated at 400hp. Many of these engines made close to or above 500 foot pounds of torque as well. The Quadrajet is an excellent carburetor and was well refined by the '70s.

This brings up another question: Were there any differences in engine internals between the carb and EFI cars in '76? GM was very fond of using different heads and camshafts on 2bbl vs. 4bbl engines, so it would not surprise me at all if there were similar differences between carb and EFI on these Cadillac 500s. Not to mention differences in timing curves.