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No Fuel Flow Into Injectors on 1994 Cadillac Concours

While I have systematically tried to fix this problem over the last 6 months, I have not been able to get fuel to flow from the fuel rail into the injectors on this 4.6 L Northstar engine. I have 40 PSI of fuel at the fuel rail, and the engine will crank but not start. If I put starting fluid into a one of the cylinders, that cylinder immediately fires and then stalls. I have checked the wires going to the injectors and they seem fine, as well as replacing the ECM and fuel pump. The fuses for the injectors are good, so they should be getting electricity. Any ideas would be greatly appreciated.

Typically, the injectors get 12v and the ECU grounds the circuit to squirt the fuel. Are you getting 12v to the injectors?

What does the “noid” do when you plug the wire going to the injector into it?

You need a measurement to verify the injectors are being electronically pulsed correctly. The car’s shop manual will have the procedure. On my Corolla – irrespective of the fuel pressure – the injectors won’t pulse unless the ECM has first determined the engine is rotating. Besides asking your mechanic to check on the correct electrical pulse to the injectors, check the crank and/or cam sensors too. And have all the diagnostic trouble codes read from the ECM memory. A faulty relay in the fuel injection system could cause this too.

Another thing to look into is the security system may be shutting down the power to the injectors.

Because the injectors are under a cover it is not possible to crank the engine and test the electrical connection to the injectors. There are not any codes showing on the diagnostics indicating a problem with the injectors nor does it show that the security system is activated. I was wondering if it might be the security system as a mechanic who used to be at a Cadillac dealer suggested that could be the problem. However the cost to test at the dealer is $400, and I first would have to get the car to them. Is there any way to determine if the security feature was activated?

“Because the injectors are under a cover it is not possible to crank the engine and test the electrical connection to the injectors.”

??? Then take off the 4 nuts holding the plastic cover off and access the injectors.

When you try to start the car, take notice of the “security” light on the dash. With the key on engine off the light should not be on. If it is, then anti-theft is keeping the car from starting.

This will be easy enough to figure out if you can get to a garage that has a scan tool old enough to access the control system on your car. Your car is old enough that I wouldn’t rely on trouble codes to get you anywhere. But the scan data showing up should give you enough information to get started in the right direction.

Thanks very much for your comments. The manifold I has a cast aluminum cover and if it is removed and the car is started it will race uncontrolled. The injectors are sealed inside. I have checked for a current and did not get any reading. There is not any security light on the car. The OB1 codes indicate a transmission shift problem but the codes do not show any engine issues. I know that it has ignition since I can prime a cylinder and get combustion,. I have replaced the start relay and checked all the fuses relative to the injectors. The Engine had periodically stalled when driving but then would restart right away, until one day it stalled as I went to my office parking lot and it would not restart since then. I have visually looked for broken or shorted wires but have not been able to find any, so I may have no choice but to get a Cadillac dealer to test the system.

Does this car have the resistor in the key. It can cause the car not to start. If you have another key you can try it. Since it’s injector related, the signals need to be checked at the ECM. I have seen a bad MAP cause this on a later GM vehicle.

Thanks for them suggestion on the chip on the key. I had thought of that and tried 3 other keys to no avail.

The idea about the MAP sensor is intriguing . In the past when this was bad I would get a P039 code, but it certainly is worth a try to replace the MAP sensor since it is tied into the same wiring harness!

Cast aluminum cover on a Northstar hiding the injectors? Can you post a picture of this? I don’t recall ever seeing that on a Northstar.

You say you have a way to get fault codes, are you using the DIC panel or do you have a scan tool to talk to the car? With some live data stream this should be pretty easy to figure out.

Looking at the wiring diagram that @knfenimore very helpfully provided it shows that power to the injectors comes from fuse A5 and passes through a few connections along with a splice point. The ground return side of the circuit for the injectors is controlled by the ECU, which is pretty common. You stated earlier you saw no power getting to the injectors so you need to look into why this is. Even if the security system is shutting down the injectors it appears that you should still have voltage getting to them since the return side of the wiring is how the circuit is controlled. Make sure the fuse is getting power to it and if that is okay then it would seem there is a bad connection in the wiring to the injectors, possibly at the splice point. NOTE: The ignition needs to be turned ON for power to get to the injectors.

Cast aluminum cover on a Northstar hiding the injectors? Can you post a picture of this? I don't recall ever seeing that on a Northstar.

On the older Northstar engines (I forget which year it started with), the “beauty cover” is actually a functional part of the intake manifold, unlike my 98 where it is just a cosmetic piece.

In the 1993 1994 Northstar engine they had the MAP sensor and the injectors sealed under a cast aluminum cover. You cannot run the engine with the cover removed as everything is understood by the pressure in the sealed manifold. Thus testing things get a bit more challenging.

Ahh, I had forgotten about those. I guess it’s been a while since I’ve had a 20 year old Northstar in the shop. The newer ones keep me busy though.

If it runs with fuel added and you have pressure at the rail you have an injector control problem. At this point I would need a complete engine wiring diagram and use a scope or graphing meter to test at the injector subharness. This will involve backprobing individual wires, and more tools than the average DIY has at home.

If no voltage is getting to the injectors, as the OP seemed to indicate earlier, this should be a fairly easy problem to fix.

In al the years I have worked as DIY on cars this is the first time I have been stumped. It appears that the Northstar engine is complicated enough despite it’s being a 1994 that it really needs some more in depth diagnostic than a DIY person can run as the Autozone type tests are no more helpful than what I can read right from the OB1 system in the car. I had thought as you, Cougar, that no voltage to the injectors would be easy to find but without being able to find a broken wire or a short, I just do not know where to look. I have been going back and forth with folks on the Cadillac discussion boards, and have just hit a “brick wall” with ideas. From what asemaster kindly assessed, it sound honestly like I have to decide if the car is worth putting about $3000 minimum into as it also developed a head gasket leak and the transmission does not want to shift out of 2nd gear despite my replacing the shift solenoids. A retired Cadillac service man suggested the cheapest way to fix this may be to get a 1995 or 1996 engine and transmission with 60,000 miles and replace both for $3,500 which is the least expensive solution I have found if I cannot figure this out myself. Your input on this before I spend more money fruitlessly will be greatly appreciated!

The key can be bypassed by adding resistors in the ignition circuit. Resistance can be read using a multimeter.

It’s really not that complicated if you have mechanical inclination, an understanding of electricity, good service information, a decent voltmeter and a logical thought process.

Forget relying on trouble codes. You’ve isolated the problem to no injector operation. A fuel injector has a constant battery voltage and a switched (pulse) ground. Since you can’t access the injectors directly, you need to find the wires that run to them. Test for power there, test for pulsing ground there. You’ll have to backprobe or pierce wires to do this.

But FYI, head gasket leaks are often the end of the road for a Northstar if you’re on a budget. You’ll have to tap and re-thread the engine block if you ever got the heads off.

I had just started to follow your logic and found where the harness for the injectors goes and connects on the drivers side of the car. Your comment on the head gasket leak is my biggest dilemma, as the least expensive fix I have found is the offer of the now independent Cadillac mechanic to replace the engine and transmission with a low miles 1975 or 1976 plus the torque converter for around $3500. The body is still in excellent shape, so as much as it hurts it might be worth more to sell for parts than to invest enough to make it a long term car to drive. I have replaced most of the brake lines but had the rusty one behind the gas tank broke when I replaced the fuel pump, so I have to fix that, and when the engine would be replaced it needs to have the evaporator core replaced in the A/C. With the age there can always be more. It is not a collector car like my 1973 Grand Am with its 7.4 liter engine, so I may have to cave in and decide it is not worth the money to fix this up. It would be good to at least get it to a point where it runs and I could drive it locally.