how does the ECU manage Fuel cut?

[Andrew7DG]

The reason I am asking this is because first I think my ECU is bad and is triggering fuel cut when it shouldn't be like just cruising around, this could be because of the MAF-T or other reasons but I think it is causing my car some problems. For example my car is randomly shutting down.

I am putting in a standalone system and for right now I want it to take over just the fuel portion of the system, not spark. I want the stock ECU to control that right now. However when the stock computer hits a fuel cut where it stops the injectors, does the timing get effected at all? Can I run the standalone system passed fuel cut and not get any problems from the timing portion (exept for knock- I know it pulls timing for that)?

 

[JayRolla]

I know that once the ecu reads too much air for the maf it cuts the fuel. Could be a bad maf. You sure its fuel cut, ive never seen it happen just cruising.

 

[Andrew7DG]

Really I am not sure whats going on...

I think it has to do with the ECU though

I have narrowed it down to the fuel injectors i think

It has to be fuel related some how. What happens is that the car will drive normally and then suddenly it seems like the car shuts off. Then after I pull it to the side of the road I try to start it again and it runs for 1 second then shuts off. After waiting some time the car will start up and run like normal and i manage to get it home. It is almost like a bad fuel pump.

However I installed a walbro 255 a while ago and I can hear it run. Not only that, I rewired it so that it is activated by a relay. I did that recently hoping that it would fix the problem. I can still hear the fuel pump when this problem happens so I know that the fuel pump can't be the problem.

The other think that I could think about is that is has to do something with the FPR but it is an aeromotive FPR and I haven't heard of these being faulty, plus the guage is reading that there is fuel pressure...

So it has to be something to do with the fuel system. I don't think spark would be causing these symptoms. The symptoms point toward fuel too much for it to be spark. I do have the MAF-T and was wondering if that could be causing problems. However I am not getting any check engine lights (that would be too easy to solve with MMcd)

Why do I think the fuel cut is faulty? Well the thing that led me to this was that I thought I had it solved by rewiring the fuel pump. I did some agressive driving when the car wasn't acting up and hit fuel cut accidently. Killed the engine. Then to my surprise it started to do the same symptoms as it did like it when it cuts randomly. It would run for one second then kill. Then after some time has passed, it would start up like normal and I drove it home with it killing one more time on the way home.

This is all I have to go by

However I have a standalone (which I am thinking I should just take over fuel and spark at the same time). I was wondering what does the stock ECU do when it hits fuel cut or if it reads passed the fuel cut (or air flow point from what I understand). Does it retard spark at all? but agian might as well just take over spark and be done with the system.

Engines are easy to fix... electrical problems are hard....

 

[Maxboost1010]

Can you get a log that we can see?

 

[delta448]

I am putting in a standalone system and for right now I want it to take over just the fuel portion of the system, not spark. I want the stock ECU to control that right now.

How do you do that? I didn't think it was possible to use both at the same time.

The other think that I could think about is that is has to do something with the FPR but it is an aeromotive FPR and I haven't heard of these being faulty, plus the guage is reading that there is fuel pressure...

How much pressure?

So it has to be something to do with the fuel system. I don't think spark would be causing these symptoms. The symptoms point toward fuel too much for it to be spark. I do have the MAF-T and was wondering if that could be causing problems. However I am not getting any check engine lights (that would be too easy to solve with MMcd)

I wouldn't rule out spark completely just yet. The MAFT could possibly be an issue, but I'm thinking it's simpler than that.

Why do I think the fuel cut is faulty? Well the thing that led me to this was that I thought I had it solved by rewiring the fuel pump. I did some agressive driving when the car wasn't acting up and hit fuel cut accidently. Killed the engine. Then to my surprise it started to do the same symptoms as it did like it when it cuts randomly. It would run for one second then kill. Then after some time has passed, it would start up like normal and I drove it home with it killing one more time on the way home.

Does it feel like "hitting a brick wall" when it happens? How sure are you that it's hitting fuel cut? What idc's or airflow frequency are you seeing on MMcd?

I was wondering what does the stock ECU do when it hits fuel cut or if it reads passed the fuel cut (or air flow point from what I understand).

The sensor will read above it (especially if you're using a GM MAF), but the ECU doesn't accept the values and determines fuel cut be executed. Fuel cut removal is often offered by vendors who do eprom chip burning.

 

[tenn-gsx]

Try swapping out your transistor. A telltale sign of a bad transistor is sudden cutting and stalling, dropping a cylinder or 2, and/or tach going haywire.

 

[steve]

The reason I am asking this is because first I think my ECU is bad and is triggering fuel cut when it shouldn't be like just cruising around, this could be because of the MAF-T or other reasons but I think it is causing my car some problems. For example my car is randomly shutting down.

Have you pulled the ECU and checked it for the classical leaking capacitors. The car randomly shutting down is a typical symptom.

 

[Andrew7DG]

Can you get a log that we can see?

working on that... the data logger battery went dead and I would have to drive out and run a log again.

How do you do that? I didn't think it was possible to use both at the same time.

I am going to be using a megasquirt system and after getting advice from people, I have decided to just take over fuel and spark with the MS system.
However the system has options if you want to take over fuel and/or spark. Simply you just would let the stock computer in place and let it take care of spark. It would think that it would be also controlling fuel but really MS would be doing that work. With MS, you control how much fuel the engine is getting. It takes its inputs by MAP. So no duel MAS sensors. Also it is not like a piggy back system because it is not changing how much air the stock computer is seeing. Unlike a S-AFC where it changes the air that the computer sees. S-AFC have the problem then of controlling bigger injectors because of this reason. However when hooked up with the MS system, I can run 1150FIC injectors with out having it mess up the timing portion.

However again, I am just going to have the MS system handle both fuel and spark completely. I am going to have the stock system in place still and use MMcd to log to see where values should be at. should help with tuning i would think...

How much pressure?
I wouldn't rule out spark completely just yet. The MAFT could possibly be an issue, but I'm thinking it's simpler than that.

Pressure should be 38 psi with the line off. Thats what it was around when it was running and when the fuel pump was primed

I am hoping it is simpler then what i am thinking... I am going to be putting back in the stock MAS to see what happens to see if that fixes anything. I have heard of coil packs giving out before however usually one give out before the other and the car is left running on two cylinders. This isn't the case though. The car is only working some of the time.

Does it feel like "hitting a brick wall" when it happens? How sure are you that it's hitting fuel cut? What idc's or airflow frequency are you seeing on MMcd?

Under the time where I was accelerating I did hit fuel cut and it did feel like hitting a brick wall. It was after that when I was getting the symptoms. Thats how I came to the conclusion that it had to do something with fuel. Fuel cut triggered the problem somehow.
I should mention that the first time that I had problems, I wasn't accelerating but was making a left hand turn and the car died in the middle of the intersection kind of embarrising... After I pushed it into a parking lot and let it sat, I tried starting it again and it ran fine for me, or untill it decided to quit again...

Try swapping out your transistor. A telltale sign of a bad transistor is sudden cutting and stalling, dropping a cylinder or 2, and/or tach going haywire.

this may sound dumb but which transitor? in the ECU?

Have you pulled the ECU and checked it for the classical leaking capacitors. The car randomly shutting down is a typical symptom.

I did check and they all looked good. However this doesn't mean that they are good. I think I am going to replace them anyway... just incase. However I though that the leaking capacitors led problems with the fuel pump and thats what gave the randomly shutting down symptom. Fuel pump isn't shutting down. I will still replace them however



Just wanted to say thanks for all of your help! very helpful ideas, will let you know what happens after this. I would like to get it working normally before I install the stanalone. Really it doesn't make sence to install something when something else is broken or could hurt the computer that I am putting in.