Hello all. I have an 89 Bronco with a 351w EFI. The motor has been pulled, bored 20 over and had all internals replaced with new. It has had all external sensors (except MAP) replaced. New MSD distributor, Ford racing wires, upgraded coil, new plugs, vacuum lines and O2 sensor. EFI has been completly gone over and cleaned.
When I got it back from the mechanic it was running rough, but he said it needed time to break in and that the timing might be off alittle. I took it to the dealership and they told me that it was running rich and had some fouled plugs. They did set the timing and clean the plugs.
The next day I started it up and it was a little rough but seemed to be running ok at idle, so I attempted to drive it to work...it was horrible! It started to have a bad miss on acceleration, ran WAY rough, the tach was jumping all over the place and being afraid of getting stranded (which is not fun in Alaska winter) I drove it back home and parked it.
The next day I limped it 5 miles to yet another shop. (Still running like crap). They confirmed that it was running rich and made some Tweaks to the engine. They did a thourough diagnostic, changed the oil, replaced the plugs and made some minor adjustments. Oh yeah, they changed out the O2 sensor again. They said the only code it had was something about the EGR not closing or something, but that it was ok. They also said that 2 of the cylinders had slightly less compresstion than the others when I first brought it in.
That afternoon I went to pick it up (a warmer day) and it seemed ok. On the way home I noticed a slight miss, so I turned around and took it back to the shop. I had the mechanic test drive it and it did it for him too. He suggested that I drive it for a while and see how it did. That was yesterday.
This morning I hopped in it to go to work and guess what? On the way to work it did the exact same thing it was doing before I brought it to the shop! (Note - it was 16 degrees out this morning) By this time I was pissed so I drove it on to work anyway. It sat there for several hours and I started it up and drove it home (Outside temp now in the mid thirties). It ran much better, only a slight miss.
So...now that I've written a novel, does anyone have any thoughts on what this could be? I'm wondering about the air temp, but everything I've tried hasn't worked and I'm considering setting the thing on fire...except that I now have almost six grand into it.
This actually happened to my 94.... I'd like to blame the mechanics who rebuilt the engine but they been doing there job a lot longer than I have been alive. So what we ended up doing was buying a brand new crate 351 and slapping it in and then sold this one for about 3 grand. So....... I don't believe that was the news you were wanting to hear......
I must be missing something here. If it was not running correctly why didn't you take it back to the first mechanic and have him either correct the problem or return your money instead of going to another mechanic ?
I am with Untamend. time for you to get your hands dirty, get your self a haynes or chiltons manual also.
is the motor getting up to the correct temp? ask the first shop what temp Tstat was installed as this is very important. Double check that the plug firing order is also correct. warm the engine up before you mess with the timing, should be at 10* btdc with spout connector removed.
now was this motor a flat tappet cam motor or a roller motor? this matters because there are different cam break in procedures and if they were not followed properly the cam could have lost a lob.
check for vacum leaks and pull codes yourself, do both the KOEO and KOER. again make sure motor is up to temp.