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To follow up on what Tom says, I don't sense that you have ruled out a problem with the fuel injectors. Even with a massive vacuum leak, the car should run at higher rpms. At a minimum, place a finger on an injector while you are cranking it and see if they are even clicking. And do the checks Tom described involving pulling the fuel rail and squirting into cups. Etc.
Here are some gizmos I made up to insert into the intake of 944s and 928s. Put about 10 psi of shop air on the fitting and just listen. Bad vacuum leaks will be very obvious. Application of soapy water will isolate them. In the case of the 944, get some PVC closest to the ID of the J boot. Remove the AFM to get good access to the J boot inlet.
Sorry I am not going to read through all of the above posts.
You need 4 things for the engine to run and I would check it in order from 1 to 4 and include the result in your reply and I can help you get the car started. Over the years I have dealt with 100s of no start conditions in different cars including many 944s from ignition lock electrical broken to bad DMEs.
1. Fuel. All you need is a can of $4 starting fluid. Spray it in the intake in pulses for 10 seconds while cranking the engine. If it continues to run, it is a fuel problem then you narrow it to fuel.
2. Spark. Is there spark and is it regular? Attach a plug to the spark plug wire and ground the plug to the block while you crank the car to check. Do not hold the plug with your hand or you will get shocked.
3. Compression. You did an engine rebuild. Did you do a compression test to make sure you didn't time the belt improperly and bent valves or have valves partially open when it is supposedly closed?
4. Timing. Bad timing on the belt will cause a no start/run.
I put clamps on the junction, but not to many of your surprise, it didn't start. I did hear the clicking of either injectors or lifters when I was spraying starting fluid. Do you guys have any other trouble shooting things to try? I will test for vacuum leaks again when it is nicer outside (smoke fluid stinks). Could something be clogging one of the injectors? I don't think that this has to do with injectors specifically because they were all flow tested, but I could be wrong.
When I tested the injector harness, everything came back normal @T&T Racing 12v on one pin and 10v on the other.
Acantor,
This test only confirms that under no load, ie no current flow and injectors not pulsing, there is electrical continuity between the injectors and the DME. It DOES NOT confirm the load situation, ie is. there is resistance in the wiring harness that whwn current flow the voltage drops so the injectors can not open.It takes a high voltage to open the injector before the DME drops the voltage to prevent the injector coil from overheating.
So, the test with pulling the injector rail and placing each injector in a catch cup MUST be done to verify the harness under load, injectors firing.
Testing the injectors just says the injectors are OK but the fuel injectors are ONLY one component of the fuel system.. The electrical component under load has to be tested and above and previous post explains how to test the fuel injector system under load
Last edited by T&T Racing; 04-24-2022 at 07:01 PM.
Acantor,
This test only confirms that under no load, ie no current flow and injectors not pulsing, there is electrical continuity between the injectors and the DME. It DOES NOT confirm the load situation, ie is. there is resistance in the wiring harness that whwn current flow the voltage drops so the injectors can not open.It takes a high voltage to open the injector before the DME drops the voltage to prevent the injector coil from overheating.
So, the test with pulling the injector rail and placing each injector in a catch cup MUST be done to verify the harness under load, injectors firing.
alright, I will get supplies to do this. I do not think that I have any clear cups that I don't care about. It is cold outside, and I don't want to fill my garage with fumes so I will get to that when the weather improves. Thanks for clearing things up!
I put clamps on the junction, but not to many of your surprise, it didn't start. I did hear the clicking of either injectors or lifters when I was spraying starting fluid. Do you guys have any other trouble shooting things to try? I will test for vacuum leaks again when it is nicer outside (smoke fluid stinks). Could something be clogging one of the injectors? I don't think that this has to do with injectors specifically because they were all flow tested, but I could be wrong.
So does the car continue to run when you spray starting fluid in continuous short pauses or not?
If it does, do you have a noid light to check injector pulse at the connector?
So does the car continue to run when you spray starting fluid in continuous short pauses or not?
If it does, do you have a noid light to check injector pulse at the connector?
It seemed when I did it, that it required continuous spraying. When I was not spraying, the car would start to die. I don't know if that tells you anything.
Do you have a noid light to check for injector pulse at the connector? Does the light flash? Voltage reading at the injector doesn't help and you cannot check for pulse without the noid light.
This is one of the fastest and easiest things to check. Unplug the connector to the injector. Plug in the light. Crank the car and check for light pulsing.
Last edited by Legoland951; 04-25-2022 at 12:08 AM.
Do you have a noid light to check for injector pulse at the connector? Does the light flash? Voltage reading at the injector doesn't help and you cannot check for pulse without the noid light.
I do not have one, is that something that I should look into buying?
It seemed when I did it, that it required continuous spraying. When I was not spraying, the car would start to die. I don't know if that tells you anything.
Hi Acantor,
This "required continuous spraying. When I was not spraying, the car would start to die" indicates that the fuel injectors are not pulsing or not of sufficient time to provide the fuel needed to run the engine.
I have seen check valves stuck at the pump, bad pump, bad DME, shorted wires in the injector harness, corrosion in the connector of the DME, stuck injectors, and more even if it runs on starting fluid. The noid light will simply narrow down or eliminate certain possibilities. If it pulses, it eliminates the DME, shorted harness, and anything electronic but not electrical.
04-23-2022, 09:58 AM
