Fuel pump not priming as it should. Bad CAS?

[JN1AS4]

Well I have been having an issue with my fuel pump not priming correctly. Primes for a second and then shuts off, and if you proceed to start the car it runs like crap idles at 10.0 AFR won't rev smoothly and puffs a bit of black smoke. But how ever if you unplug the CAS and prime the pump it works just fine, then I can reconnect the CAS and start the car and it runs like it should. I was just wonder if anyone else has come across this problem before and what you guys think it could be. The motor is a SR by the way.



UPDATE AS OF: Wednesday, Nov.21

My car ran perfect all the way up until this morning. I tried everything once again. CAS didnt seem to do the trick today. But I ended turning the key to the "start" position real quick but not long enough for the car to crank(bump the starter) and that seemed to do the trick. Pump primed perfectly once the key got back to the "on" position from the "start" position. I think that im getting closer and closer to finding the problem. I just haven't been able to put my finger on it just yet. COTBU shot down my theory of the CAS being the problem and i'm starting to see that now. But Its definitely something between the ECU, IGN and the Fuel pump though. COTBU please chime in again you were ALOT of help!

Thanks, James

[cotbu]

Just looking at what you said, priming the engine equals engine not running. so why would the CAS be the problem. I however see a voltage problem there, have you tried disconnecting the mafs as opposed to the CAS or maybe even the injectors.

Just to let you know when you do this, it makes diagnostics hard, because you will have a code for CAS and if the CAS is faulty you have to start over with a cleared CAS code.
so see if you can duplicated a good start up without disconnecting the cas.

[JN1AS4]

Yes I've tried unplugging the maf also, and the car ran the exact same(FP primed weird pulsating/interrupted sound). I've unplugged the battery for 1hr or so and that corrected my problem for a day or so. And when I unplug/plug the CAS with the key "ON" position but not started you will hear the pump prime perfectly smooth and I can start the car right up and it will run perfectly for the next week or so. Thats what leads me to believe that its the CAS thats slightly malfunctioning.

[cotbu]

Sounds logical enough.
Have you checked the cas wheel for warping or cracks?
Sounds more like an electrical problem.
Priming the engine koeo, the cas is used by the ecu to determine if the engine is running.
so it has little or nothing to do with the fuel pump priming, The cas itself.
so I say wiring problem, maybe even at the cas, check the voltage koeo.

[Chrischeezer]

the ECU has a built in voltage regulator for the pump, it control prime and standard running,
Id check fuel pressure and keep an eye on the voltage @ the pump when the engine is running.

CAS is in the circuit too, so your correct to suspect that as well.

[JN1AS4]

Originally Posted by cotbu

Sounds logical enough.
Have you checked the cas wheel for warping or cracks?
Sounds more like an electrical problem.
Priming the engine koeo, the cas is used by the ecu to determine if the engine is running.
so it has little or nothing to do with the fuel pump priming, The cas itself.
so I say wiring problem, maybe even at the cas, check the voltage koeo.

Nope I havent had the chance to check the CAS wheel for warping/cracking but I will do so today. And I understand why you feel as the CAS and fuel pump priming has little to no relations with each other. But they do. Its weird but CAS definitely primes the pump whenever you unplug/plug it while the key is in the "ON" position.

[JN1AS4]

Originally Posted by Chrischeezer

the ECU has a built in voltage regulator for the pump, it control prime and standard running,
Id check fuel pressure and keep an eye on the voltage @ the pump when the engine is running.

CAS is in the circuit too, so your correct to suspect that as well.

Fuel pressure is perfect(43 psi) as long as the pump primes correctly. But when the pump is acting weird its usually primes around 23-32psi, but the car runs pig rich(below 10.5:1 far) almost like its running on 3cyl. When in reality if it is the CAS its definitely possible for it to be running on 3cyl when it malfunctioning.

[cotbu]

You don't understand the system, I know as i told you what the cas does when engine is not running and what it looks for. THE CAS is not your problem! You don't even get a full prime when you disconnect the cas with koeo, you just broken the circuit so if you do get this

when I unplug/plug the CAS with the key "ON" position but not started you will hear the pump prime perfectly smooth and I can start the car right up

then I still lean towards electrical/wiring problems.
You could track down the wiring problems or spend $80 maybe for a used CAS or $299 for a new unit. the choice is yours.

just read your last post you chasing a theory, how many times does a cas fail and cause 1cyl to not fire? I don't know because logic tells me to start somewhere else.

[JN1AS4]

Originally Posted by cotbu

You don't understand the system, I know as i told you what the cas does when engine is not running and what it looks for. THE CAS is not your problem! You don't even get a full prime when you disconnect the cas with koeo, you just broken the circuit so if you do get this then I still lean towards electrical/wiring problems.
You could track down the wiring problems or spend $80 maybe for a used CAS or $299 for a new unit. the choice is yours.

just read your last post you chasing a theory, how many times does a cas fail and cause 1cyl to not fire? I don't know because logic tells me to start somewhere else.

You are correct you don't get a full prime when the cas is disconnected with koeo, but it does prime smoothly. But if you turn the key from the "OFF" position to the koeo position all while the cas is disconnected the car will prime(fully) perfect then if you connect the cas all while koeo still and proceed with starting it up from there it will start and run perfect. With perfect afs from idle/wot. I will be more than happy to double check cas wiring though. Do you know how much voltage i'm looking for at the cas with the key "off" and key "on"? The swap was performed about 5yrs ago and everything worked perfectly up until about a month ago. No wiring was touched previous to this problem occurring. Thats what led me believe it had to be a component malfunctioning. Ive pulled the pump and checked it, inspected/cleaned the maf, checked egi relays/fuses, etc. I just want my baby back to 100%....lol

[JN1AS4]

bump!!!!!!!!

[woodsmary]

Thats what leads me to believe that its the CAS thats slightly malfunctioning.

[JN1AS4]

Surprising new twist. I edited my original post with the update!

[suspectu1]

What fuel pump? Internal? External? Who installed it? It really seems like a wiring problem to me. I have wired up an sr20 into an s13 shell that had 0 wires in it and i left out the voltage regulator circuit that controls the fuel pump. I wired the pump to 12V with ignition on and a pin in the ecu to the ground of the pump. That's all you need
There's a schematic of the simplified sr20 ecu somewhere online.

[JN1AS4]

Originally Posted by suspectu1

What fuel pump? Internal? External? Who installed it? It really seems like a wiring problem to me. I have wired up an sr20 into an s13 shell that had 0 wires in it and i left out the voltage regulator circuit that controls the fuel pump. I wired the pump to 12V with ignition on and a pin in the ecu to the ground of the pump. That's all you need
There's a schematic of the simplified sr20 ecu somewhere online.

Walbro 255. I installed it. The pump isn't the problem, now the pump wiring may be though. Seeing that the oem fuel pump harness/connectors are +20yrs old now. I would really like to just fix the issue. But hard wiring the pump is the nxt option. I had a buddies car that had +12v wire coming straight from the ecu(idk which pin), but everything else(ground, signal, etc.) came from the factory fuel pump harness/connector. Do you have any info/write-up of how to perform the re-wiring of the pump?

[suspectu1]

Originally Posted by JN1AS4

Walbro 255. I installed it. The pump isn't the problem, now the pump wiring may be though. Seeing that the oem fuel pump harness/connectors are +20yrs old now. I would really like to just fix the issue. But hard wiring the pump is the nxt option. I had a buddies car that had +12v wire coming straight from the ecu(idk which pin), but everything else(ground, signal, etc.) came from the factory fuel pump harness/connector. Do you have any info/write-up of how to perform the re-wiring of the pump?

yes sir! just to make sure you understand how the fuel system works on these (and most other) fuel injected vehicles;
1. the fuel pump needs 12V positive and a GND to operate.
2. you can either switch the (+) or the (-) on any device and have it turn on or off.
3. in our case the +12V is provided by a relay that gets current going to the pump as soon as you have your keys to the ON position (ignition). This is where i think you misunderstood the system. The ECU does not provide positive voltage to anything! it only switches the ground of the different electrical loads.
4. it's up to you to decide if you want the ECU to control the pump, or have a manual switch to turn it on and off (i have mine wired through a Painless switch with a momentary on position for priming).
5. if you still want the ECU to switch your pump on and off, then you will need to locate pin 104. This is where you need to ground your fuel pump, well technically your fuel pump relay.

If i haven't lost you, here's what i recommend:
Go buy a new 30amp SPDT relay from radioshack or whatever.

Install it near the ECU.
Locate the wire coming from pin104 of the ECU (black and pink).
Locate a wire providing 12V with the key on the ON position.

Wire the relay as follows:
crimp a 12Ga wire to the one you found earlier (that provides 12V with key ON);
have the end of this wire go to pin 30 of the relay;
make a small 16Ga wire going from pin 30 to pin 85 on the same relay (this is to provide both power and switch the relay);
crimp a 16Ga wire to the black and pink wire coming from pin 104 of your ECU;
have the other end of this wire going to pin 86 of the relay (this is what i was referring to when i said the ECU switches the GND of your fuel pump relay);
pull a 12Ga from pin 87 all the way to the (+) on your fuel pump;
pull another 12Ga from the (-) off your pump to anywhere on the chassis.
You're done!

This way you will have a completely new harness to control your fuel pump, not using ANY of the old stuff to avoid having to track down electrical issues.

[suspectu1]

this is what the diagram looks like for the OEM system. The voltage regulation module is wired from pin 86 of the fuel pump relay therefore it controls it's ground. It only goes to pin 104 on the ECU after this module.
We get rid of this by wiring the coil of the relay straight to pin 104 of the ECU.

[JN1AS4]

Originally Posted by suspectu1

yes sir! just to make sure you understand how the fuel system works on these (and most other) fuel injected vehicles;
1. the fuel pump needs 12V positive and a GND to operate.
2. you can either switch the (+) or the (-) on any device and have it turn on or off.
3. in our case the +12V is provided by a relay that gets current going to the pump as soon as you have your keys to the ON position (ignition). This is where i think you misunderstood the system. The ECU does not provide positive voltage to anything! it only switches the ground of the different electrical loads.
4. it's up to you to decide if you want the ECU to control the pump, or have a manual switch to turn it on and off (i have mine wired through a Painless switch with a momentary on position for priming).
5. if you still want the ECU to switch your pump on and off, then you will need to locate pin 104. This is where you need to ground your fuel pump, well technically your fuel pump relay.

If i haven't lost you, here's what i recommend:
Go buy a new 30amp SPDT relay from radioshack or whatever.

Install it near the ECU.
Locate the wire coming from pin104 of the ECU (black and pink).
Locate a wire providing 12V with the key on the ON position.

Wire the relay as follows:
crimp a 12Ga wire to the one you found earlier (that provides 12V with key ON);
have the end of this wire go to pin 30 of the relay;
make a small 16Ga wire going from pin 30 to pin 85 on the same relay (this is to provide both power and switch the relay);
crimp a 16Ga wire to the black and pink wire coming from pin 104 of your ECU;
have the other end of this wire going to pin 86 of the relay (this is what i was referring to when i said the ECU switches the GND of your fuel pump relay);
pull a 12Ga from pin 87 all the way to the (+) on your fuel pump;
pull another 12Ga from the (-) off your pump to anywhere on the chassis.
You're done!

This way you will have a completely new harness to control your fuel pump, not using ANY of the old stuff to avoid having to track down electrical issues.

Thank you so much. I will definitely be using this if I cant sort out my problem soon. And one more quick question, where does the 87A pin on the relay go?

[suspectu1]

If you look the first diagram I posted, the SPDT relay has two poles that can output power. 87a is not used in our application because it provides 12V before the coil gets energized. Since we want switched power to the pump, we use the 87. Get a relay and put a multimeter on the 30 and the other lead on the 87a. You'll see it has continuity. Now try 30 and 87 and it shouldn't show continuity unless the coil is energized.

[JN1AS4]

I got a better understanding. Thank you very much!!!!

[JN1AS4]

Problem solved: faulty ignition switch!