76 Seville dies when given gas

[Jasperwashere]

Car will start up every time but even a light touch of the gas pedal causes it to die out and if I just leave it to idle it will die on its own in a minute or so.

I was considering it could be the fuel pump giving out, as it's much quieter than it was before and there doesn't seem to be much pressure coming from the shrader valve. I wanted to know if there's anything else I should dig into before jumping to conclusions though. These EFI systems are tricky.

[TJ Hopland]

We have a couple people here that really know that system well and even make some parts and do repairs on them so I'm sure one or both of them will be along soon with some specifics.

It does seem likely that you have a fuel pressure issue especially since you noticed a change in the sound which may indicate one of the pumps isn't working or maybe they are not getting enough voltage.  Voltage is apparently a common issue where the relay and traces on the ECU board get overheated and damaged. 

[bcroe]

Assuming the timing chain set is not bad yet,
lack of fuel could be caused by low fuel pressure
or a bad MAP inside your ECU.  The temp sensors
give extra fuel to a cold engine, then with warm
up that could go away and the engine dies. 

Use the manuals to check out the fuel pressure. 
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.

With good fuel pressure, your ECU probably
needs work.  I have been checking and repairing
these for a couple decades, email me for more
info.  bcroe AT SIGN juno DOT com
Bruce Roe CLC # 14630

[79 Eldorado]

As Bruce recommended you really need to have a copy of the blue and white manual. I do like having a hard copy and I do have one but I also use the pdf frequently which was posted for download on this site.

See post nr 6 of this thread:
https://forums.cadillaclasalleclub.org/index.php?topic=167249.msg511579#msg511579

Here's the table of contents. Decide which item best describes what's happening with your car. They have nice trouble shooting fault diagrams after that.

Scott

[Jasperwashere]

Thank you I will go through these diagnostic tree.

[Jasperwashere]

Ok, so I've maybe crossed some possibilities out but haven't pinpointed the issue. Fuel pressure checks out, increases with throttle (on the rare occasion I can get a rev out of it). Pump seems to be fine.

Forgot to mention before the fast idle switch is busted and bypassed with a small washer inside the plunger. The car was running and driving with this fix done previously. However, the car will not run if it is pushed down completely and will run at very high rpm if the washer is removed. So it is capable of reaching higher RPM than idle but even then it will die if given throttle.

Really leaving me scratching my head here. And keeping an eye out on Marketplace for a good intake to just carb convert this s.o.b.

[bcroe]

Probably the ECU is not giving enough gas,
very common when the internal MAP sensor
fails.  I can replace those if my ECU tests
indicate that problem.   Bruce Roe

[Jasperwashere]

What do you charge for that?

[badpoints]

Also check the vacuum line going to the MAP sensor. I wonder if there is a way to put the ECU into a default mode like newer cars when the MAP sensor is bad.

[bcroe]

What do you charge for that?

A new MAP, some other parts these cars all need,
and return postage in USA is less than $100. 
Email me as I indicated in my 1st post. 
Bruce Roe CLC 14630

[79 Eldorado]

"Car will start up every time but even a light touch of the gas pedal causes it to die out and if I just leave it to idle it will die on its own in a minute or so."

Is everything going on before the car even has time to warm-up? I know you're mentioning an issue with the FIV but it seems like you must be overcoming that issue if you're checking other things. I am making FIV replacements. Price is best on Junkyardfind. Very nice site even though it's difficult to completely avoid eBay. Here's the link:
https://www.junkyardfind.com/1975-80-cadillac-efi-fiv-fast-idle-valve-choke-heater-replaces-1628898-1181290-a-5173.html

If it was dying because you you don't have enough initial FIV bypass, with the washer installed, you could also temporarily open your idle screw some. The total air with the throttle blades closed is the combination of the FIV plus through the opening the end of the idle screw allows.

When you touch the throttle you are opening the throttle plates so the fact that it's dying with a "touch of the gas pedal" does seem to say you have another issue (other than the FIV).

Bruce is incredibly fair with his ECU repairs. I would also suggest one of his external relays which he could ship back with the ECU.

Also be aware that a lot of people blame things on the EFI system which aren't even things specific to EFI. Something as simple as a fuel filter is an example. I read a thread once where the person converted and used the existing pump but never bothered to check the condition of the soft line in the tank. I don't recall what he used to regulate the pressure down to around 5-7psi which is typical for a carb. Anyway you will figure it out and once you do these cars run quite well.

Scott

[MeToo]

It couldn't just be a blockage in the fuel line or pump somewhere?

[bcroe]

It couldn't just be a blockage in the fuel line or pump somewhere?

Yes that is why fuel pressure is checked.  Bruce Roe