Hello All, I am new to the forum as well as new to owning a 928. I just bought a 1981 928 US model 5 speed. It didnt come with a fuel pump or a fuel filter. I have replaced both tonight and the car will start for just a second then it will die. It will run longer if I pour gas down the intake. The fuel pump is running and seems ok. The Brain was replaced and the person I bought it from said it tested ok. When the car starts for the second it does it dies ASAP. If you push the gas peddle it wont start at all. Any suggestions? Please help!!!

 

Might be your fuel pump relay, #17. Check out 'fuse and relay charts' at this site. http://www.928gt.com/

Good Luck

 

I will look into that tomorrow. I thought the relay would not let the pump run. This one runs all the way until the engine dies then it stops running right after that. Its just like some thing is telling the injectors to go then stop even though the pump keeps running.

 

Here is whats happening. The cold start fuel injector is not controled by the ECU. Instead it provides a large amount of fuel to serve as a choke for the engine, to get the combustion chamber coated in fuel. This greatly improves the engines cold start. The cold start injector is controled by a thermo-time switch. It fires for only a few seconds at each cold start up, and not at all in a hot start up. It is completely independent of throtal position. When you start the car, this injector is fireing, allowing the car to run for a moment, BUT will not fire more to allow for anything other than idle throtal, and shuts off a few seconds after start up.

The other 8 fuel injectors are controled by the ECU, and it's associated sensors. Some how, on your car, all 8 injectors are not fireing. Your job is to find out why.

1. There is the "AFC" or "Fuel Injection" relay in the passanger's foot well fuse/relay pannal. Go to www.928gt.com to find out exactly which one. If the relay is not working for some reason, there is no juice getting to the EFI system.

2. One of the main sensors for the EFI system is disconnected. Without the sensor connected, the system shuts down. Check the AFM, and Temp II sensors. The AFM is the meter bolted to the bottem of the air cleaner box. The Temp II is the vertal sensor near the oil fill, under the corss brace along the center line of the car.

3. One of the grounds for the EFI system is disconnected. There are 4 ground for the system. All ground wires on the 928 are brown. One ground for the EFI is on the frount cross member. (The peice of metal infrount of the radator.) It is a 10mm head bolt pointed to at the radator, dirictly under the head light shaft. There is one each side of the car. Clean both, but the EFI goes to the passangers side one. There is one on the farthest foward intake runner, on the passangrs side. There is one in the right rear wheel arch, behind the pannaling, and finaly one more underneath the steering console. Once you get under the steering console, this one is hard to miss.

Good luck. There are more possibilitys, but these are the most likely.

PS, since you know the fuel pump is running, it is not the fuel pump relay.

 

Cool, Thats going to give me a lot to do tomorrow. I will start running down all of them in the morning. I didnt know about the cold start injector thing. I will let you know tomorrow what I find. This is all new to me. I am used to building old chevy's. I have always wanted a 928 and now I have one it is like learning cars all over again.

Thanks for your help.

Tres

 

Is there another relay I can use to test to see if that is it?

 

Sure, just be sure to cross check the part numbers on the relays, in accordance to the relay page on 928gt.com (Btw, the specific page is under the technical spec. page.)

You can also build a jumper. Just be sure to make the jumper have 3 plugs. There is one power, but two collectors for that relay. Both of the terminals marked 87 need power.

 

Best to start with checking spark (use caution, spark can kill). Have you pulled the spark plugs and verified they are functional? Are the cap and rotor in good condition?

In addition to fuel issues, look for possible vacuum leaks too.

 

Rich, spark issues shouldn't cause his problem. He can milk the car by pouring gasoline down the intake, which means the engine is getting psark but not fuel. Also, I don't know of much of anything will with cause those symptioms. The ignition system it's pretty much all the way on, or all the way off. I really can't think of anything that would cause the ignition system to kill the engine a few seconds after it starts.

However, I do know from experence that that is exactly what happens when the main 8 injectors don't fire for some reason.

 

Good morning guys. Well, I went and check all the grounds as well as the relay and the connections to the AFM and the TempII and they all are conected. The relay is clicking and I even switched it out with another and no luck. I am starting to think that maybe the Brain is not working properly. The person I got it from said it was good but then again you just never know. Any other suggestions? Oh, and I am getting good spark.

Tres

 

Are you sure you have to correct relay? Also, it's not just enough to check the grounds. Pull them off and clean them. It doesn't take much corrosion, and sometimes it's invisible.

The ECU is very reliable, usualy it doesn't get fryed. Besides, you don't want ot buy one, they're pricy and only pretty much only avalible used.

OK, next, I would confirm that you get power to the injectors with the key on. A test lamp, or volt meter is fine. They get their power from connectors W2 and W3 on the fuel relay board. The connctors are the plastic plugs accrost the bottem of the board. They are lettered A, B, C, D, D... from left to right. However, around M or P, they stick Z in there for some odd reason. Anyways, you need W. The plastic connectors are marked by hand with their letter.

From there, I would pull the connector off the ECU, and confirm that your getting the power from the injectors. The injectors fire when the ECU provides them with a ground. It's pin numbers 15, 33, 32, 14 on the ECU terminal.

Next make sure your getting power from the relay to power the brain and the circuits. This is a wire in the harrness from W4 to pin 29 AND W5 to 10 on the ECU.

From there, I would start checking the resistance of the indivdual sensors, but thats alought to talk about in t a post.

 

Have you checked to make sure you are getting sufficient fuel from your new pump ie the new one could be bad?

 

Ok, I will start checking there and get the test light out. I pulled all the ground wires off and cleaned them with a wire brush as well as cleaned the bolts and the mounting surface. I then put it all back together. The relay that is in is the right part number according to the 928 site you gave me.

Jim, I havnt put a gauge on the fuel rail yet but I am going to. I did however have the cap off of the end of the fuel rail and it shot out a 3' long stream of gas, ooooopppss.

 

Yea, you ought to get a better results that this out of that 3' long stream of gasoline.

Something is keeping the 8 injectors from opening.

Good luck.

 

Cool, thanks. I will let you know what happens.