1970s 1976 Cadillac 500 fuel injection

[V63]

There were no internal
engine differences that I am aware of.

The distributor was specific however.

The fuel tank was special.

[smokuspollutus]

One advantage to the port fuel injection that was unique to the Cadillac big block was the elimination of the overall poor performance of the upside down intake runners with a wet intake. Fuel injected big blocks (when working right, at this point few of them are unless they've been sorted) do idle smoother, tip in better and pull harder without the atomization bottleneck the intake design encouraged.

Ironically they stepped backwards in this regard with the DFI system in 1980 which necessitated a wet intake again. 

The same basic system when used on the Olds seems to have less butt dyno power than the 4bbl version.

I found the fuel injection to actually be more thirsty than the carburetor.

[V63]

The Cadillac big blocks were incredibly smooth and nice throttle response. Agreed on the fuel economy...very heavy beasts. The 75-79 Seville always seemed under powered... adequate but lacking.


One thing interesting about the Bosch system from 1975-80 (1980 California), was that when Mercedes had it before Cadillac, it fired in
4 phases (2 injectors each) but Cadillac only had 2 phases (4 injectors), that has to be less efficient and I always wonder why that was changed.

[bcroe]

My opinion, the Seville needed the small block
403 engine, which is a direct bolt in for the
350.  Just retune the EFI a bit (like my car),
but unfortunately the EFI started for 76 and
403 was not available till 77.  The other thing
it needed was better gearing.  Unfortunately no
4 speed auto was available for 76, and the switch
pitch TH400 was long gone.  Again a bolt in, the
latter took a whole second off my 0-60. 

I know little of the Bosch, but have not seen it
as having a lot in common with the Cad EFI. 
Firing a high side driven peak/and/hold injector
bank requires a medium power circuit with heat sink,
so using 2 instead of 4 definitely has cost and
space savings.  Bruce Roe

[TJ Hopland]

IF you were to go with a modern aftermarket EFI system I think there would be many downsides to using the original EFI intake.  There was nothing even remotely standard about how anything fit that intake.  The TB flange was unique.  I think the injector diameters and heights were also unique so you would end up having to modify a lot of thing to still end up with some oddball stuff that may be hard to source parts for. 

I believe the Edelbrock intake has flat areas ready to be drilled for injectors and then you also have a standard TB flange and non of the linkage clearance issues you get with the Cad intake.   Just about anything that isn't a Q jet will have clearance issues with what ever hangs down below the throttle shaft on a stock intake. 

The stock intakes are 'upside down' because of the Eldorado being FWD.  The Eldo engine sits up high to leave clearance for the drive shaft to go below the crank and they apparently decided to use the same intake on all the cars rather than have the Eldo have its own.   

[MultipleCaddies]

The way things are all adding up, I'm going to go carbureted. I just don't see the benefit of putting the time, money and effort into this EFI system when I know a carb setup will be rock solid reliable. Plus, I already have a spare intake and a fresh Quadrajet ready to go, so there is little for me to have to search for.

I'm also quite confident that with appropriate carb and distributor advance curve tuning, I'll be able to make up for the difference in power output and maybe a little extra. Emissions era tuning was NOT geared towards best performance, but I have no such concerns with that now. I'll be using an earlier non-EGR setup on it, eliminate the smog pump, and tune it for best performance. Wouldn't surprise me if I find a couple-few dozen long lost horses in this thing.

[79 Eldorado]

I've been heavily into my entire system. When I bought the car I was afraid of the unknown. I'm having one problem currently but I will work through it. The system is complicated but at the same time not really. I really like the EFI system and there's no way I would get rid of it after getting deeper into it.

If the prior owner was correct, pumps were not coming on, then you need to determine why. The fuel pump relay is inside the ECU and Bruce, who has replied here, has mentioned that high percentage of ECUs have damaged/burned pins powering the pumps. He has a preventative measure fix which is an external FP relay. I installed it on my 79 and documented it for others to follow here:
https://forums.cadillaclasalleclub.org/index.php?topic=153100.msg414525#msg414525

The white and blue book was posted by a member and is also commonly available on eBay. See post nr 6 of this thread: https://forums.cadillaclasalleclub.org/index.php?topic=167249.msg511579#msg511579

Replacement injectors are available. I sealed mine with flourosilicone o-rings instead of the ones commonly in the kits because flourosilicone should be better if you plan to run alcohol containing fuel and alcohol free.

Temperature sensors are incredibly easy to check, speed sensor incredibly easy to check. Fuel pressure port is in an easy place to attach a gauge on my car.

My tank was very clean, from Texas, I even found a build sheet on top of the tank. Mine could have convinced most people it was NOS new after I used a dry toothbrush to remove the Texas dust. I changed the in-tank pump but the OE worked. The soft line looked a bit like a marshmallow but it wasn't hard and it didn't appear to be leaking.

I do plan to now replace the in-tank once again but with a high pressure pump to go to a single pump system. The problem I'm having seems to be fuel volume related. My high pressure pump works but under load it doesn't seem that it's up to task anymore. There are external replacements but none seemed to be perfect drop-ins.

Because it's a maintenance item which you would likely change be careful with the fuel filter gasket. Mine started leaking not long after acquiring the car and once recently. I did find that the AC Delco GF157 filter comes with a seal which is taller than the one I removed. It was just over 4mm instead of 3mm and that filter gasket blew-out on me. I questioned it when I installed it but it was AC Delco so they should know what they're doing. I would avoid repeating that like the plague. I don't like FRAM filters but the FRAM replacement, which could be sourced same day while 70 miles from home, had the roughly 3mm thick gasket. The AC Delco gasket had lipped out of the filter housing lip.

You can do what you want but the OE EFI system is pretty nice. It has no feedback so it only knows what the inputs tell it. Two temp sensors, TPS, speed sensor, and MAP sensor inside the ECU. As a safety item, if the speed sensors stop, then the pump power is killed.

I guess your problem could be the ECU main fuse blew or the ECU pins are burned, or possibly something happened where it isn't getting the signal from the speed sensors. You can see if the pumps come on by powering a wire which unplugs just behind the tank. At least that's where it is on my car. It's in a separate, single wire, connector which looks a lot like an early Delphi weatherpack.

Too cool to dump the EFI and either way you need to go through the system. The in-op will likely be something simple if you take the time to diagnose it.

Scott

[MultipleCaddies]

I'm less concerned about diagnosing whatever the issue is now and much more concerned about real world reliability in the long run. I'm contemplating a trip to Florida in this car in a few months, and the last thing I want is an unreliable car for a 6,000+ mile roadtrip. The lack of easy parts availability is a big concern out there on the road, especially parts that I can't easily fix myself on the side of the road.

I'm going carb. I'm going to post this whole system for sale I think. I know once I remove it, it will never go back on the car, and this car isn't in any kind of collector quality condition where it will fetch any real money if I ever sell it, so I'm not concerned about retaining it. If anyone is interested, let me know. I'll be getting to it in the next couple weeks here.

[Chopper1942]

79 Eldorado,
You can check the pump volume by connecting you fuel pressure gauge to the port on the rail and removing the hose from the gauge. You should get a pt of fuel in just a few seconds. Check the specs. If it's low, pull the high pressure pump inlet line and see the low pressure pump passes a volume test. If not, I would suspect that the "marshmallow" coupling from the low pressure pump to the fuel line on the sender is leaking causing the low volume issue. Also, have you checked the dead head pressure of the high pressure pump? If you pinch off the return line from the fuel rail, the original Bosch pump would develop over 100 psi new. If your pump developes 80+ psi it work OK. Max regulated pressure is only around 60 psi.

[79 Eldorado]

Larry,
It acted basically the same after I changed the in-tank pump which included submersible Gates hose and clamps. I did also pinch-off the return line and I got about 65psig. I thought that was a number you mentioned in another post and because it seemed like a good check I did it. That check was before I changed the in-tank low pressure pump. I only changed the low pressure pump at the time because I had an exhaust appointment, 140 mile round trip, which I may not have been able to reschedule until next year. It wasn't running perfectly but I made it. Had I had more time I would have gone directly to a single high pressure pump but I would have needed to have one in-hand and I did not.

Exhaust is done and I added an AFR gauge. Today I replaced the in-tank with a high pressure pump; Walbro GSS342. This car just seems to want more work done to it and it always seems to know when it's within 500 feet of the garage. There's more to it, even more than I listed below, but I don't want to continue to go off-topic.

MultipleCaddies mentioned a long trip. Most of the work I've had to do has nothing to do with the EFI system. The timing chain on my car had the nylon coating and the factory aluminum intake started to weep. I went through everything sitting on the intake when I changed it. I also realized the front cover was leaking at the balancer area, balancer was worn, so now it's new. I put a re-manufactured starter on it because the starter solenoids are now more than half the cost of replacing the starter. That starter worked perfectly for 2 weeks until the solenoid would kick the Bendix but the starter wouldn't turn. The new starter came and it had a short solenoid. My car has a battery cable with a molded plastic guide on it to keep it in exactly one position as it passes by the right side output shaft. That meant the shorter solenoid caused the positive cable to be short by 3/4". AutoZone went out of their way to get the proper solenoid on the starter and all was fine but out of curiosity we ordered another starter and it came with the correct solenoid... once again all was fine, this time for 10 days, and then the rear of my oil pan developed a leak. I had to pull the final drive out to do that job and of course the starter again. I could now do a starter on the car wearing a blindfold.

It's very possible that the 1976 is easier to find parts for but my point is these are old cars and, at least in my case, you cannot always get the parts in the same day even for a carburetor version like my 1979 Toronado. When I was doing the intake I did rebuild the distributor as a non-ESS version. That was because that is essentially the "only" part which "we" (the 70's EFI owning community) has not come up with a solution for and like MultipleCaddies I didn't want a failure which I didn't have a solution for.

MultipleCaddies, remember that the fuel supply is on the driver side, not the passenger side like most GM carburetor cars of that time, so include some planned re-route to what you need for conversion. Or possibly you could use an in-tank pump and simply find a regulator for the lower pressure required by the carb. I think that's the way I would probably do it. So you could retain the aft part of the EFI. You could also still signal the pump(s) with the ECU controlled relay and you could keep the speed sensor set-up for the safety of shutting off the pump. If you did that then you would at least have the benefit of not having to pump the crap out of the carb system after storage when the fuel evaporates from the fuel bowls or leaks as was common with the original QJet bowls.

One other point about the age of these cars. When I rebuilt my distributor I realized that my pick-up coil wire was about to break. Even though it was a pick-up coil which supports a 5 pin module the problem was not specific to EFI. That could be a time bomb in any 40+ year old car.

Scott

[MultipleCaddies]

All of the typical old car foibles are old hat to me. I've resurrected many a neglected vehicle, I know not to try to chase foreseeable issues one at a time as they come up, but simply address them all ahead of time. I restore classic American muscle cars professionally, and part of that comes with the knowledge that 50 year old cars are absolutely full of worn out parts. Doubly so when old cars sit for half their life. Trying to limp them along fixing one thing at a time as they break just results in endless frustration and builds resentment with the car. Totally counterproductive. If you're going to own and drive a classic car today and want to actually put some miles on and enjoy it, you have to be proactive and address all of the common, predictable issues before you try to drive it. Hence why I'm so hesitant to run an old EFI system where most of the parts just aren't available any more, and even at it's best is still more complicated and potentially unreliable than a simple carb setup.

What I've actually decided to do in the meantime is prep a known good running 79k mile 472/TH400 combo that I have sitting here and swap it into the car for now instead. All gaskets and seals on both engine and trans will be replaced, new fuel pump, new oil pump, new water pump, it already has a freshened up Quadrajet with ethanol-resistant needle and accelerator pump, a new Pertronix distributor, new plugs and wires, new timing chain and sprockets, and most importantly it's a proven good runner that I've put some miles on. I'll set the original 500/TH400 aside for later freshening up.

I'll investigate this fuel tank, and if need be I'll swap it out with a standard carbureted tank (since people say they're different). I will absolutely NOT run a needlessly unreliable electric pump setup with a 50 year old computer that can leave me stranded for no reason. Making a fresh new hard fuel line from tank to engine is easy, I've made many such lines. Nicopp and a two post lift make it a nice easy job, along with fresh ethanol-resistant stainless braided hose at both ends. A fresh new mechanical pump is extraordinarily unlikely to fail any time soon with regular use. And once this car is an established good runner, it will get regular use. My drivers do not sit for extended periods, they get used. Plus, ethanol-free fuel is readily available where I live, so apart from long road trips, it will always get ethanol-free fuel anyway.

Among other things this car will get before any long trips are all the brake hydraulics replaced or freshened up, all the axle seals and gear oil changed, front bearings repacked or replaced as needed, u-joints likewise, power steering hoses changed and fresh fluid, all coolant hoses and either a new or recored radiator, etc.. I won't leave anything mechanical to chance to before a long road trip. None of this is new to me. I've watched and learned from the many mistakes and tribulations of others, as well as my own experiences, to know better than to leave things to chance when driving old cars. They need a lot of attention, and I want to ensure that I get to decide when and where said attention is given, not wait for the car to tell me somewhere between Flagstaff and Gallup, or somewhere equally desolate where no parts or services are to be had. When you do the work yourself and know that it's done right, and you cover all your bases ahead of time, it really makes it so much easier to really enjoy a classic car. I have to make my customer's cars absolutely reliable for them, and I put the same effort if not more into my own.

I'll still carry a spare carb kit with me, probably a spare fuel pump, an old distributor and wires, and of course fluids. And thanks to some good wholesale closeout deals at Rockauto, a whole bunch of extra belts! Just in case. But with everything fresh I don't expect to need any of it.

[79 Eldorado]

MultipleCaddies,
One thing Cadillacs of this era seemed to be lacking was even a basic gauge set. In 1979 The Toronado came standard with a coolant temp gauge but you couldn't even get the Eldorado with an optional gauge pack. My point is , regardless of carb or EFI, it probably wouldn't be a bad idea to at least have a temperature gauge. Using a gauge you can often see something is happening before it becomes a real problem. I don't know your particular model well so not certain what they came with.

Scott

[jwwseville60]

To justify the expense of EFI, Cadillac probably fudged the numbers so customers would feel better. Only an engine Dyno or rolling road would tell the answer. Who can honestly feel a modest jump in power on a Sherman tank-torquey 500?

I worked with Mercury outboard engineers in the late 1980s. When they put EFI on their new motors the BHP didnt change much at all, maybe 5-7 bhp. But they advertised it as a 20 bhp plus advantage.

[bcroe]

One issue with small motors in the past, has been
lack of good spark advance control.  My 2000 tractor
(20hp) had fixed timing, so it only was optimized
for one load and rpm point.  Most EFIs these days
fix that with a programable multi dimension spark
table.  I adapted one of the spark advance controls
to the tractor (the carb stayed) and it made a huge
improvment to overall performance, and approximately
15% better fuel mileage.  I can imagine a similar
improvement on the outboard.

However, only with the 80s digital EFI did the Cad spark
advance get upgraded.  The 70s stayed with a pair of
2 dimensional systems, independant vacuum and rpm
advances only.  Bruce Roe