: 94 Seville Backfire- Cracked Intake Manifold on startup.



sts-ej
03-22-07, 02:09 PM
94 Seville Backfire- Cracked Intake Manifold on startup.

Hope someone can help,
First time when it cracked the intake I bought a used intake manifold and I was advised to replaced the crank sensors and also I had a used ignition control module with coils and repleaced that to. Car started and run great for a week then it slowly was hard to start each time and just like the first time it backfired and cracked the intake again with smoke.
I have checked the compression 150 to 155 all cylinders, fuel pressure 0 psi when key off for 1 hour key on 36 psi and would drop to 0 after a hour. There are no fuel leaks any were. No codes
I did see looking down in the intake values on number 1, there is large a spacer that sits between the block and the intake, it had a brownish look to it, all the others are black. I suspect thatís where it backfired from. (Attached photo)
What to do next? Fuel regulator, Fuel pump?

eldorado1
03-22-07, 02:55 PM
Looks like your intake valve is crudded up. If it's holding the valve open, it can easily backfire through the intake.

Most likely cause is a leaky valve seal. You'd have to pull the head to fix the problem.

Or is the one on the right the "normal" one? The one on the left could be being washed with fuel (leaky injector). Kind of hard to tell from your pics, but there is definately some major carbon buildup on the right one.

Ranger
03-22-07, 03:59 PM
Based on fuel pressure bleeding down, my guess would be a leaky FPR. On the '93/'94 it is inside of the manifold so fuel would pool there. With the intake cover off, turn the key on to energize the pump and pressurize the system, but DO NOT crank the engine. If no fuel leakage is noted from the FPR nipple, let is set for an hour and check it again.

sts-ej
03-22-07, 05:39 PM
I did pressurize the system a couple of times and checked for leaks and didn't see any fuel around the FPR or anywhere else. I have remove all the air flow
tubes from the bad intake to see everything around the fuel rail and FPR.
I did notice that when installing fuel rail/gasket it didn't take much pressure
to seat the FPR not like the return side I had to push much harder. I was expecting to see it leak from the FPR but didn't see anything, I'll repeat pressurizing the system a few more times.
Question about fuel pressure how long does the pressure hold with key off?
I cannot find this in the service manual.
Thanks Ranger

eldorado1
03-22-07, 06:25 PM
Just because you don't see it leaking doesn't mean it's not leaking.

If the injector is sticking, it might only start to dump fuel when it's running. (i.e. receiving pulses to open)

Fuel pressure should stay steady for hours. If it drops more than 5psi in an hour, then it's got a leak somewhere. My car will hold some pressure till the next day... What is the pressure at key on engine off? Should be 45psi +/- 3-5psi.

What is the pressure when idling? Were you able to get that info?

sts-ej
03-22-07, 07:13 PM
I was not able to get the fuel pressure when idling.
The one on the left is the one I was concerned about
that maybe leaking fuel. I know there is a tester$$ to
check fuel injectors but all I did was measure resistance
50 ohm. Should I buy a new injector at this time or is there
some other test I can do?
Wouldn't I see error code on receiving pulses to open?
Also the wire harness for the injectors/sensors some of the wires
seem to fused together in some spots. I did do a resistance check
before I seperated them (no shorts) I still need to inspect wires for
defects.
Thanks
Eldorad01

Ranger
03-22-07, 08:14 PM
Theoretically, it should hold pressure forever. In reality, you may have a leaking check valve in the pump, which is bleeding fuel back into the tank.

To check for a leaky injector, lift the fuel rail. Have somone turn the key on while you look for a leaking injector.

eldorado1
03-22-07, 08:26 PM
I was not able to get the fuel pressure when idling.
The one on the left is the one I was concerned about
that maybe leaking fuel. I know there is a tester$$ to
check fuel injectors but all I did was measure resistance
50 ohm. Should I buy a new injector at this time or is there
some other test I can do?
Wouldn't I see error code on receiving pulses to open?
Also the wire harness for the injectors/sensors some of the wires
seem to fused together in some spots. I did do a resistance check
before I seperated them (no shorts) I still need to inspect wires for
defects.
Thanks
Eldorad01

50 ohms would be bad. Should be reading around 12-18 ohms. Compare to the other injectors' resistance readings.

You can probably buy a populated used fuel rail for the price of a tester (~$100), so choice is yours.

If one injector is sticking, you might have a bank fuel difference code set. Depends on how much it's sticking.

Also, another thing to check later is your MAP sensor. Intake backfires can take them out. You'd need a service manual to find out the procedure for checking the correct barometric and idle readings. That's after you fix the problem though.

sts-ej
03-22-07, 09:46 PM
Sorry for the 50 ohms I went out and checked they are all 11.8 to 12 ohms.
I've bought a service manual at the time I bought the car.
I should be able to test the check value buy sealing off the return line and see if it holds pressure, about 65 psi?

eldorado1
03-22-07, 10:21 PM
The check valve is in the supply line. It prevents the fuel from leaking back through the fuel pump to the tank.

The FPR (should) already seals the return line. On the other side of the FPR the fuel line has no pressure, since it just dumps to the tank.

sts-ej
03-23-07, 10:15 AM
Thanks you guys for all your help. This is my first Cadillac and I'll sone
replaced with newer STS black/Black.