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19K views 51 replies 3 participants last post by  gornati 
#1 ·
I have a 78 coupe, with the 425 EFI, it starts everytime easily, engine is good, but if engine gets hot and i turn it on, i have to wait a long time, before i can start it again.

Any advise on this?

Thanks
 
#5 ·
For openers, I would check the 2 EFI temp sensors. Then test the ECU to make sure its delivering the right amount of fuel under all conditions. The MAP sensor in those ECUs often fails. If consequently injector pulse width is reduced, the engine will start on cold enrichment but falter when hot. Swap a spare ECU if you have one. Otherwise, I'll check the ECU for postage. I have a new MAP replacement circuit (no originals available) if its needed. See stuff on Cad 70s EFI on my PHOTOBUCKET

http://s93.photobucket.com/albums/l71/bcroe/

(that is a lower case "L"71, not an upper case "i"71)

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

Bruce Roe CLC #14630
 
#7 ·
For openers, I would check the 2 EFI temp sensors. Then test the ECU to make sure its delivering the right amount of fuel under all conditions. The MAP sensor in those ECUs often fails. If consequently injector pulse width is reduced, the engine will start on cold enrichment but falter when hot. Swap a spare ECU if you have one. Otherwise, I'll check the ECU for postage. I have a new MAP replacement circuit (no originals available) if its needed. See stuff on Cad 70s EFI on my PHOTOBUCKET

http://s93.photobucket.com/albums/l71/bcroe/

(that is a lower case "L"71, not an upper case "i"71)

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

Bruce Roe CLC #14630
Can you tell me where the sensors are located?

How much the new MAP replacement?
 
#11 ·
78 it always had been my dream, had a 81 before...
77 dont have the beautifull, IMO, vertical taillights, and the 79 have way too many holes in the front grille.

this was what i could afford back in end of 2008, it is very expensive to bring those cars to Brasil, i paid originally $1700,00 for this car off ebay.

I want to have some day a H&E Convertible... maybe a 78 or a 80-84.

But first things first, let me put this one on the road first.

I have no idea on where to start, sometimes i want to start disassembling the whole car, and check every inch, but i know this is not the way to go.

How 77-79 devilles you have in total?
 
#10 ·
Check your battery cables. Not that this will help your hot start problem, but will address your general engine starting. Remove and closely check your ground cable. Swelling along the insulation is an indication of corrosion. The original cables were made of aluminum cable, and over time they oxidize and corrode. Replace if neccessary. Make sure youe cable ends are clean and that your contact surface is clean also.
There is also a ground strap at the starter, make sure it's connections are clean also.
One of my cars has an additional strap to the engine block because of grounding problems.
 
#13 ·
I have no idea on where to start, sometimes i want to start disassembling the whole car, and check every inch, but i know this is not the way to go.

How 77-79 devilles you have in total?[/quote]




I know what you mean. I've got a couple cars I'd like to rip to the bones and start back up again. In fact I'm doing that with one of my coupes.

I think I have 15. I had 2 others, but I let them go. Catch and release program. Several are parts cars and some need attention and evaluation. I'm looking at a nice '79 that is for sale at a local dealer, but not sure I want to add anymore cars to my collection at this time. :hmm:

I see someone bypassed the relay circuit board and installed a switch, eliminating the relay. Does the toggle switch regulate both high and low speed circuits?
A lot of people do this because the heat generated at the relay burns out the relay board.
 
#14 ·
I have no idea on where to start, sometimes i want to start disassembling the whole car, and check every inch, but i know this is not the way to go.

How 77-79 devilles you have in total?



I know what you mean. I've got a couple cars I'd like to rip to the bones and start back up again. In fact I'm doing that with one of my coupes.

I think I have 15. I had 2 others, but I let them go. Catch and release program. Several are parts cars and some need attention and evaluation. I'm looking at a nice '79 that is for sale at a local dealer, but not sure I want to add anymore cars to my collection at this time. :hmm:

I see someone bypassed the relay circuit board and installed a switch, eliminating the relay. Does the toggle switch regulate both high and low speed circuits?
A lot of people do this because the heat generated at the relay burns out the relay board.[/quote]

Eliminate which relay? sorry if it seems a dumb question...
 
#15 ·
GORNATI,

The air temp sensor is in a runner from the carb to
a cylinder. The water temp sensor in the coolant
somewhere; I've seen them at the thermostat or in
the back pipe to the heater. They are interchangeable,
should measure around 1000 ohms at room temp. If
only one is good, make sure it is in the water till you
get another.

I don't charge to check out your ECU. But postage &
customs could be a problem here. Most ECUs need
something; I usually recommend getting them checked
so you can cross it off the problem list. If your
pulse widths are OK, the MAP is probably OK too.
Keeping a spare ECU can help, though people that
far away sometimes just give up the fuel injection and
put on a carb.

I'm retired, advisor to the CLC (Cadillac LaSalle Club). I
think their web site is under construction for a few days.
I don't often sell ECUs, but if I had your model, it
would be a small fraction of the $350 the Ebay guy
wants. Don't know who that is, I wonder if he can
test & repair them as well as I do?

Lots of ECUs are marked "REMANUFACTURED". Not
to worry, they are OK but renumbered. If you give me
your email, I can send a list of ECUs and what they fit.
And my EFI checklist. I'm bcroe@juno.com

The usual problem with mixture, is a failing MAP
sensor in the ECU. If it is putting out low voltage
now, it will soon fail completely. Its on picture 10
(SH 8) of ALBUM-78 K ECU SCHEMATIC. Notice
that there is a test point VMAP where you can measure
the MAP voltage, a 5 pin connector on the side. Or with
ignition on but not running, no hose connected, you
can remove the cover and and measure the MAP voltage
at its pin, or wire jumper 13. It should be 9.5V input,
7 to 7.5V output. The 7V will drop to 0-2V as vacuum
is applied. The hose to the ECU connects to the MAP.
If it is failing, I could install one of my replacements.

Once the engine is hot, your ECU should put out a
fuel injector pulse width around 4ms at idle, 8 ms at
cruise, and near 12ms at Wide Open Throttle.

deVille33 also gives good advice. Most cars that age
should get a new timing chain; the original cam sprocket
has plastic teeth which fall off, block oil flow, and let
pistons hit valves. You can check it without taking the
engine apart.

good luck, Bruce Roe
 
#16 ·
GORNATI,

The air temp sensor is in a runner from the carb to
a cylinder. The water temp sensor in the coolant
somewhere; I've seen them at the thermostat or in
the back pipe to the heater. They are interchangeable,
should measure around 1000 ohms at room temp. If
only one is good, make sure it is in the water till you
get another.

I don't charge to check out your ECU. But postage &
customs could be a problem here. Most ECUs need
something; I usually recommend getting them checked
so you can cross it off the problem list. If your
pulse widths are OK, the MAP is probably OK too.
Keeping a spare ECU can help, though people that
far away sometimes just give up the fuel injection and
put on a carb.

I'm retired, advisor to the CLC (Cadillac LaSalle Club). I
think their web site is under construction for a few days.
I don't often sell ECUs, but if I had your model, it
would be a small fraction of the $350 the Ebay guy
wants. Don't know who that is, I wonder if he can
test & repair them as well as I do?

Lots of ECUs are marked "REMANUFACTURED". Not
to worry, they are OK but renumbered. If you give me
your email, I can send a list of ECUs and what they fit.
And my EFI checklist. I'm bcroe@juno.com

The usual problem with mixture, is a failing MAP
sensor in the ECU. If it is putting out low voltage
now, it will soon fail completely. Its on picture 10
(SH 8) of ALBUM-78 K ECU SCHEMATIC. Notice
that there is a test point VMAP where you can measure
the MAP voltage, a 5 pin connector on the side. Or with
ignition on but not running, no hose connected, you
can remove the cover and and measure the MAP voltage
at its pin, or wire jumper 13. It should be 9.5V input,
7 to 7.5V output. The 7V will drop to 0-2V as vacuum
is applied. The hose to the ECU connects to the MAP.
If it is failing, I could install one of my replacements.

Once the engine is hot, your ECU should put out a
fuel injector pulse width around 4ms at idle, 8 ms at
cruise, and near 12ms at Wide Open Throttle.

deVille33 also gives good advice. Most cars that age
should get a new timing chain; the original cam sprocket
has plastic teeth which fall off, block oil flow, and let
pistons hit valves. You can check it without taking the
engine apart.

good luck, Bruce Roe
Yesterday i found what looks like a loose sensor, will take a picture and post it here, then i will check them sensors.

My ECU is indeed remanufacturated, but im thinking about getting another one, just in case.

I sent you an email so you can send me that info you offered, i accept it :)

After the eletrical part is ok, i will start checking the timming, belts and cam sprocket.

Im taking notes of everything you guys told me so far, my first daughter is about to born, so i dont think i will have the time to do everything in the next 2 weeks, but i keep you all posted.

Thanks

C. Gornati
 
#17 ·
Eliminate which relay? sorry if it seems a dumb question...[/quote]




No dumb question. Above the brake pedal and to the right, there is a board with several relays attached to it. You will find an area in the top left corner which is burned out. Your fan / temperature control relay used to plug in there.

Your fan circuit goes to a series of coils up in your air control box, which sense the temperature of your air box and determine fan speed. The signal goes back to the relay and switches the circuit from high to low, so your temperature control is automatic.
 
#18 ·
Just a quick update wich may give some information for you guys help me..
Sorry for being a little indivdualist on this one...

Well, my camera has no batteries, while they are charging, i decided to go out and drive around the block with the caddy.

Turn the car on, start at the first turn of the key, idle is extremmly high, i have no tachmeter, but looks like it is between 1500 and 2000 rpm.

Car is cold and when i pump it looses rpm and almost dies, if step on the gas it will shut off (any ideas?)

Left the car running for almost 8 minutes, then idle goes to normal i am able to pump on the gas and the car will not die, did the maneuver to take the car off the garage, i live in an apartment and the biggest car here is a ford ranger, it is very hard to remove the car.

After that iam able drive in the neighbordhood, car runs good, could not get a lot of speed, brakes are not 100%, i would say stopping power is about 15% now...

So the question is, what could be causing the car to have such a high idle and not be able to pump on the gas when the car is cold?

After is hot, idle is normal and runs like a deer...

Will take some pictures of what i think it is a lose sensor and pictures of some wiring i found disconnected.

Again thanks you all
 
#21 · (Edited)
Well finally had the time to take some pictures...

Here is what i think it is a sensor, if it is a sensor, what sensor is this?

This is located right before the cruise control, diaphragm.



I dont know, things are slow now here, still need to get the licence plate to take the car to be washed down and have the brakes done.

So, little by little you all help me out.
 
#26 ·
well bruce, your dang right, the thing i think it was a sensor is the cruise control link.

today i drove the car for a while, brakes are terrible, but after filling up the tank, engine died, but easily turn back on.

I think that could be some old gas and dirt on the lines also.

today i also redone the center panel wich was disasembled.

Next week i might already have the new brake booster and master cilinder, after that with brakes will be much more easy to take the car to shops and fixing all the stuff.

Today is mothers day here in brasil, so i had a very shor time to mess with the car, next saturday will be good, i will wash the car, fix some eletrical problems.

Regards to you all.

Thanks again Bruce and DeVille33
 
#34 ·
Well besides the MAP sensor, is there any other problems in the eletronic/sensors, that could be causing this problem?

Now i think i have to clear the injectors, change their o-rings etc...

There is 2 solenoids, in the vacuum lines, do you have any idea on how to test them?

This problem could be connected to the vacuum lines?

my car is a california car, but some dumb machanic installed the wrong TVS sensor, i already purchased a new one there i will be getting tonight.

With this new TVS i will be able to leave my vaccum lines exactly as it was when came from the factory.

Any new ideas?
 
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