1976 Cadillac eldorado convertible efi

[JuneBug]

My 76 cadillac eldorado convertible sat for a few years. The guy said it was running good ladt time he drove it. He said it needed a fuel pump. I got both fuel pumps,strainer, and two fuel filters, clean and sealed the tank after finding bad gas in the tank. Car starts up for a minute, sounds good then putters out. I have no clue what the problem is I got fuel pressure. A fella I had look at it today said the tps... is it the tps??? Anybody please help!!

[Scot Minesinger]

hard to diagnose this over the internet, Bruce is an expert and should be responding soon.

[JuneBug]

Yeah,  any helpfull hints is much appreciated!!

[Jeff Rosansky CLC #28373]

The o rings around the injectors are probably bad due to age. Be careful that you dont have a fuel leak/fire.
Bruce will get you up and running but I just wanted to chime in asap to be sure you dont have a problem while you are trying to figure it out.
Jeff

[JuneBug]

Thanks Jeff!!!

[bcroe]

My 76 cadillac eldorado convertible sat for a few years. The guy said it was running good last time he drove it. He said it needed a fuel pump. I got both fuel pumps,strainer, and two fuel filters, clean and sealed the tank after finding bad gas in the tank. Car starts up for a minute, sounds good then putters out. I have no clue what the problem is I got fuel pressure. A fella I had look at it today said the tps... is it the tps???

First, its NOT THE TPS.  Everybody blames it, but it only has some influence as you
increase the throttle.  It sounds like either way rich, more likely way lean.  It may
do the same thing with the ECU unplugged and some gas poured down the throttle
body.  If your fuel pressure is about right (39 psi or less), very rich is likely caused
by a failed Integrated Circuit in the ECU, easily replaced.  Also make sure the vac
hose from the throttle body to the MAP inside the ECU, isn't leaking.  Too lean, first
check the EFI temp sensors for around 1000 ohms cold and not infinity.  Ok, then
the most likely cause is a failed MAP sensor inside the ECU. 

Those ECUs can fail about as easily on the shelf, as running.  I test the 75-79 ECUs,
and have a replacement for the odd, very early MAP.  Bruce Roe CLC # 14630

[Glen]

Bruce,
Does this year car have the oil pressure switch for the fuel pump?  From the symptoms my guess was that the engine gets fuel when the key is turned to on, but that only supplies enough to start the car.  When the engine starts the oil pressure switch turns on the fuel pump.   

Tell me if I am way off base here. 

[bcroe]

Bruce,
Does this year car have the oil pressure switch for the fuel pump?  From the symptoms my guess was that the engine gets fuel when the key is turned to on, but that only supplies enough to start the car.  When the engine starts the oil pressure switch turns on the fuel pump.   

Glen, These EFI cars (and likely all other EFIs too) sense engine rotation electronically
("speed sensors"), not by oil pressure.  The ECU directly controls the power to the
fuel pumps.  Unfortunately the pump current flowed directly thru the ECU resulting in
burned connector contacts eventually.  That is why I have been pushing an external
fuel pump relay (kit), to avoid ECU damage.  Just like all later EFIs.  Bruce

[JuneBug]

Thanks Bruce!! This car is a pain in my back side!! I learned a lot with this car. I have a buyer for it, no longer my problem... I know when I buy another get the one with a carburetor. You guys are awesome. Bruce are you knowledgeable with the 80's Cadillac Eldorado 4100?

[bcroe]

Thanks Bruce!! This car is a pain in my back side!! I learned a lot with this car. I have a buyer for it, no longer my problem... I know when I buy another get the one with a carburetor. You guys are awesome. Bruce are you knowledgeable with the 80's Cadillac Eldorado 4100?   

Whoever owns the car, it will worth infinitely more if it runs.  My best guess is
that $60 and an hour spent on the ECU (MAP) will solve the problem; if not at
least the possibilities won't be an ECU fault. 

I have a 79 Eldo with the early EFI standard, which is why I know about these
systems.  Two months were spent getting it in shape for the meets last summer,
very little of that time was spent on the EFI.  Anyone who doesn't want to fix
their old cars probably should just own a Honda.  I would be infinitely happier
with mine or yours, than anything with a 4100.  Don't know how to fix them.
maybe its impossible.  good luck, Bruce Roe

[JuneBug]

The one I have is a project.  I want one I can paint and put nice rims on and that's it...I have a couple other projects, 2 money pits is a enough. Thanks again Bruce!!

[Glen]

Glen, These EFI cars (and likely all other EFIs too) sense engine rotation electronically
("speed sensors"), not by oil pressure.  The ECU directly controls the power to the
fuel pumps.  Unfortunately the pump current flowed directly thru the ECU resulting in
burned connector contacts eventually.  That is why I have been pushing an external
fuel pump relay (kit), to avoid ECU damage.  Just like all later EFIs.  Bruce

Hummm…I’ll have to see if I can figure out where I got the oil pressure switch idea. 

Thanks Bruce

[TJ Hopland]

Does this year car have the oil pressure switch for the fuel pump?  When the engine starts the oil pressure switch turns on the fuel pump.

GM did to that at times so you didn't imagine it.  Really not sure why.  It makes some sense as a safety feature if there is not any sort of computer but like Bruce said the ECU knows if the engine is turning or not so it would seem pretty simple to just have a circuit that said fuel pump is only on if cranking or engine is turning.   Maybe that took too much processing power in the early digital days and the didn't have it to spare?   In 94&95 they did it with the 6.5 diesel trucks.  There was a relay that made the fuel pump run when cranking but other than that the oil pressure switch directly ran the fuel pump, no relay or nuthin.   People that own those used to remote mount the sensor to make them easier to replace because they went out so often.   If you didn't let the engine fully warn up and shut it off you would hear the pump still running from residual oil pressure.

In the electric choke days oil pressure is what ran the choke.   They did that so if you for some reason turned the key on but didn't start the car the choke would not start to unwind.   Ford used a special terminal on the alternator that was only live when it was spinning. 

[bcroe]

Cars were built in the 70s with a low pressure pump in the tank feeding a
carb.  I think the 70s EFI just took that design and added another high
pressure pump.  Not an elegant design, saved time avoiding the immediate
design of a high pressure tank pump.  Bruce Roe

[TJ Hopland]

Which cars had an electric pump with a carb?   I don't think I have heard that before.  Seems like an odd design choice for the time. 

[bcroe]

Which cars had an electric pump with a carb?   

76 Vega for one; don't know what others, but perhaps some carb Cads.  Bruce

[TJ Hopland]

Never seen it on a cad but I could see the Vega.   Lots of 'new' things were tried with that car.   I think that was the one they were planning on shipping vertically so there were unique design features to make that possible.  Maybe the electric pump was related to that?

[Gene Beaird]

GM did to that at times so you didn't imagine it.  Really not sure why.  It makes some sense as a safety feature if there is not any sort of computer but like Bruce said the ECU knows if the engine is turning or not so it would seem pretty simple to just have a circuit that said fuel pump is only on if cranking or engine is turning.   Maybe that took too much processing power in the early digital days and the didn't have it to spare?   In 94&95 they did it with the 6.5 diesel trucks.  There was a relay that made the fuel pump run when cranking but other than that the oil pressure switch directly ran the fuel pump, no relay or nuthin.   People that own those used to remote mount the sensor to make them easier to replace because they went out so often.   If you didn't let the engine fully warn up and shut it off you would hear the pump still running from residual oil pressure.

In the electric choke days oil pressure is what ran the choke.   They did that so if you for some reason turned the key on but didn't start the car the choke would not start to unwind.   Ford used a special terminal on the alternator that was only live when it was spinning.

The oil pressure switch-activated fuel pump probably has something to do with people not paying attention to their gauges when operating a vehicle.  If you really do have an oil pressure problem, you had better not be running the engine.  A sensor on the distributor/cam/crankshaft to see if the engine is running won't stop the engine from running if you lose oil pressure.

Most 90's-era GM cars had the oil pressure switch to keep the fuel pump running.  And yes, a bad switch can result in a pump that won't spin up after the engine starts.  And I've had the switch stick so that the pump keeps running even after the ignition is turned off. 

[JuneBug]

Bruce I want to get my cadillac eldorado convertible running. Where can I get the ecu worked on?

[JuneBug]

Running rich, I got new double platinum spark plugs and after a few starts, plugs very dirty..