Recommend an ECM to replace my 8747?

[gregs78cam]

I recently had an issue with my truck's tbi conversion. The fuel lines had gotten too close to the exhaust and it was having boiling fuel issues. It would run fine until it got warm, it would always do it, but when it did it would stumble when you got to about 30%TPS. Idle was just fine though.

The other issue I ran into recently was on a buddy's truck, where the fuel pump was not making enough pressure at any state other than idle. The thing that tipped me off was that when in closed loop it was pegging max lean.

These are just my two recent discoveries with TBI. Were your injectors replaced with the TBI rebuild? Is their power wire corroded? getting hot? not able to carry enough current? Could this be combination of issues, i.e. injectors that get flakey at low pulsewidths, such as hot idle?

A datalog might reveal some interesting trends.

[JeepsAndGuns]

I wish you were closer, especially if your pickup was a crew cab with a tan interior. I need a rear seat (employee spilled gear oil all over it) the glove box hinge piece, and I'm sure about a zillion misc pieces that I am not thinking of right now.

I haven't heard of the knock sensor being separate from the ECM. Can you elaborate on that more? Thanks.

The knock sensor is always seperate from the ecm, its threaded into the block somewhere. Its the knock filter I was talking about. Its what recieves the signal from the knock sensor when there is knock, and then sends a signal to the ecm to retard timing. The knock sensor and knock filter are engine specific. On yours, its the squareish shaped flat box with about 4 wires going into it, should be mounted beside or under the map sensor on the right of the intake. (it was on the truck I am parting out anyways)
On the later pcm's (such as the 16197427) the knock filter is part of what is called a memcal. It has the main prom chip, the limp home chip, and the knock filter all in one removable unit in the pcm. The V6 and 5.7 memcals are easy to find, but a 7.4 memcal is not as easy. You could use a 5.7 memcal, and re tune the chip to work with the 7.4, but the knock filter will be incorrect and the knock retard will not function correctly. It could either pick up false knock and retard your timing, hurting performance, or not pick up knock that is there, and then your engine could get damaged.

[dpilot83]

I think the vapor lock theory is losing traction after today. I used it a fair amount today. One time I drove about 15 miles, stopped for 15 to 20 min to eat and then started it again and it had a tough time starting. Outside air temp was 64 degrees F (18C) at that time. Lots of cloud cover here today.

The next example was more significant I thought though. I stopped to help my wife clean the church after another 20 mile drive. When I stopped I immediately opened the good to help it cool down faster. We probably spent 15-20 min finishing the cleaning of the church. We decided to go eat afterwards so. I started my pickup to park t more out of the way in the parking lot. It started fine and I ran it for maybe 1 minute changing parking spots. I did not open the good this time because I figured it would not have warmed up much. We spent probably 30-40 minutes eating and came back to get the pickup. It barely started again and ran really rough until I got it revved to 3000 RPM.

So whatever it is, I think it's getting worse. I'm quite puzzled that twice today it appeared to break the heat related rule. So far in the past it has only done it when it was 80+ degrees outside and it had been idling awhile.

Not so today.

i need to go ahead and get everything that I need to start logging data. I'll probably just order tonight.

[dpilot83]

The knock sensor is always seperate from the ecm, its threaded into the block somewhere. Its the knock filter I was talking about. Its what recieves the signal from the knock sensor when there is knock, and then sends a signal to the ecm to retard timing. The knock sensor and knock filter are engine specific. On yours, its the squareish shaped flat box with about 4 wires going into it, should be mounted beside or under the map sensor on the right of the intake. (it was on the truck I am parting out anyways)
On the later pcm's (such as the 16197427) the knock filter is part of what is called a memcal. It has the main prom chip, the limp home chip, and the knock filter all in one removable unit in the pcm. The V6 and 5.7 memcals are easy to find, but a 7.4 memcal is not as easy. You could use a 5.7 memcal, and re tune the chip to work with the 7.4, but the knock filter will be incorrect and the knock retard will not function correctly. It could either pick up false knock and retard your timing, hurting performance, or not pick up knock that is there, and then your engine could get damaged.

I see. Thanks for the explanation. I understood that the knock sensor was separate from the ECM (I meant to say knock filter in my previous post, sorry about that). I had just never heard of the knock filter before.