Using a ECU from a 305 with my 350?

[RecklessWOT]

Anyone know if I can use an ECU from a truck with a 305tbi with my 350tbi? In an attempt to narrow down the problem I'm having with my burb I've decided to swap out the computer and see if that makes a difference. Got my hands on a free ECU out of an 87 pickup from a guy at work. Our trucks are the same year, but different engine sizes. I assume they run different fuel maps, but will my truck still be able to run using the ECU from the 305? I basically just want to see if my timing issue goes away after I swap it out. Will it be able to run on his ECU enough for me to drive it around a little while? Even if I do make less power or lean out at higher RPMs, I will end up buying a proper computer from a truck with a 350 if need be, but I want to test it out before I throw money at something that I'm not even sure will make a difference.

 

[Georgeb]

Whats your timing issue?

 

[RecklessWOT]

Involved with the same issue that I was trying to figure out in this thread a while ago.

I don't know for a fact that it's timing related but it really feels like it to me the more I think about it and drive the truck. Basically it seems like the problem happens any time that the timing should normally change because of the electronic timing advance (similar situations that the vacuum advance would control on older models), but instead of slightly advancing or retarding like it should, the timing retards itself to the point where the truck just up and cuts out.

If I try to increase throttle to pass a car or go up a hill or merge onto the highway, it completely stops firing for a second or two. Sometimes it backfires, sometimes it doesn't. Sometimes out the exhaust, sometimes out the intake. Then it resumes running smoothly again. If the truck is idling for a long period of time (maybe when it reaches a certain temp or something) the truck will "cough" and then resume idling like normal, or once in a while it may stall. When I take off from a stop after sitting for more than a couple seconds (like when a light turns green) sometimes it stumbles and almost dies but then comes right back, other times it stalls. Sometimes it dies as soon as I shift into park after backing into a parking spot. It never runs rough, never idles poorly, never has reduced power, or breaks up, it just completely cuts out sometimes.

The issue may may not be timing related at all, but I still want to see if a new brain will make this **** stop. None of this happens while running in limp mode on base fuel and spark. Despite running rich, the problem completely goes away in limp mode. So the problem is only happening when the computer is either trying to make a calculation about fuel or timing. Unless it's a wiring problem, I can't think of too much else it could be other than the ECU. I have this other computer for it, now I just need to find out if I can use it to test this theory or not and rule out one more possibility, or if I absolutely need one for a 350.

 

[bucket]

The ECM can only adjust timing a certain amount, so I don't think your hiccup is based completely on timing, if at all.

I have run tbi 350's on a tbi 305 ecm before and they seemed to run fine, but that was with the throttle body and injectors for a 350 too. But if you have the correct ECM, it can't hurt to try it.

 

[Georgeb]

can you connect to it with a pc and log data? That will help a great deal in troublshooting the problem.

 

[RecklessWOT]

The ECM can only adjust timing a certain amount, so I don't think your hiccup is based completely on timing, if at all.

I have run tbi 350's on a tbi 305 ecm before and they seemed to run fine, but that was with the throttle body and injectors for a 350 too. But if you have the correct ECM, it can't hurt to try it.

Thank you for the response. That's good to know, kind of what I was expecting/hoping to hear.

Yeah you're right it may not be timing related at all but something weird is happening and I really want to just try to swap the computer even if for nothing more than ruling out one more possibility.
I will still be running the 350 injectors and everything, I'm gonna leave it exactly how it is now and just swap out the box, see what happens.

 

[RecklessWOT]

can you connect to it with a pc and log data? That will help a great deal in troublshooting the problem.

I have had it hooked up to a computer to monitor the sensors while driving and I didn't get much useful data. My friend has some fancy snap on scan tool/ computer thing that he can read and program all types of stuff with, that's his specialty (he's an extremely talented mechanic/ race car builder). He wasn't able to make much sense of what my truck was putting out, apparently it's doing some funky stuff.

We didn't look too deeply into it due to it being a cold rainy morning and being a little hung over from the festivities the night before, but if swapping this computer doesn't make a difference then we will certainly get back on it. I just want to try swapping the box first and hope it makes a difference. I'm no good with this kind of stuff, I have very little understanding of computers and I have no patience for it; Heh, I've even still got a 9 year old flip phone. A couple of people have already talked me out of ripping everything off and converting to a carburetor. I understand the many advantages of EFI and I really like having it, but I'm all out of ideas. It's nice being able to start my truck on a cold morning, I just don't like having a truck that doesn't run right and not knowing how to fix it...

I have tried just about everything else, Changing this ECU is not the first thing I have tried, I got to this point by process of elimination. I have a FSM and even the fuel and emissions/ driveability book but it still has me stumped. I've wasted months dealing with this turd trying to get it running right, it's driving me nuts. Barring a wiring issue, I really can't imagine what else it would be

 

[Georgeb]

I have had it hooked up to a computer to monitor the sensors while driving and I didn't get much useful data. My friend has some fancy snap on scan tool/ computer thing that he can read and program all types of stuff with, that's his specialty (he's an extremely talented mechanic/ race car builder). He wasn't able to make much sense of what my truck was putting out, apparently it's doing some funky stuff.

We didn't look too deeply into it due to it being a cold rainy morning and being a little hung over from the festivities the night before, but if swapping this computer doesn't make a difference then we will certainly get back on it. I just want to try swapping the box first and hope it makes a difference. I'm no good with this kind of stuff, I have very little understanding of computers and I have no patience for it; Heh, I've even still got a 9 year old flip phone. A couple of people have already talked me out of ripping everything off and converting to a carburetor. I understand the many advantages of EFI and I really like having it, but I'm all out of ideas. It's nice being able to start my truck on a cold morning, I just don't like having a truck that doesn't run right and not knowing how to fix it...

I have tried just about everything else, Changing this ECU is not the first thing I have tried, I got to this point by process of elimination. I have a FSM and even the fuel and emissions/ troubleshooting book but it still has me stumped. I've wasted months dealing with this turd trying to get it running right, it's driving me nuts. Barring a wiring issue, I really can't imagine what else it would be

I hear ya. I have made the decision to go with a carb on my truck as opposed to the TBI for the same reasons. Mine was just a little to finnicky and my carbed truck runs as good or better even at -15 deg.

 

[RecklessWOT]

So it ended up being the ECU after all. Plugged the other one in and it runs great again, I'm so relieved. Now I don't have to sell it!