'91 SHO code advice

[SHO n OFF]

So, I had my old motor replaced with one from a 90 with about the same mileage on it. The car sat for a good 5-6 months before this happened. Started driving it, it would sputter and backfire a bit upon takeoff. I figured there was water in the tank like before from sitting too long. So I dumped some HEET in it and the problem disappeared after about a week. But in the past 2-3 days, it's been doing it a bit more while I'm driving. To the point where if I'm on the gas it jerks picking up power then losing it. If I rev it a bit high to takeoff from a light, it'll go just fine with no backfiring, or when I'm lightly on the gas it doesnt seem to do it as much. The car has never stalled or died on me......yet. I tried swapping coils, that did nothing. The engine light only seems to come on when the car has been driven for about 20minutes. The codes I pulled today are:

21
49
77
91
And I believe I got a 14 somewhere too, unless I mis-read that.

code 91 says its running too lean. Could this be my fuel pump on its way out?Any help or advice is appreciated. :thankyou:

 

[rubydist]

21 = ect out of range
49 = spout circuit open, timing set at 10*
77 = did not open throttle far enough during koer test
91 = no switching of 02 sensor on left (front) bank

so you have several issues:

first, the engine coolant temp sensor is either dead or the connector/wiring is bad. that means the pcm always thinks the engine is cold, so it wastes a lot of gas and is generally ******* the engine. I would replace the ect sensor.

second, the pcm thinks the spout circuit is open so it leaves the timing at 10* permanently. this is great if you are trying to pass emissions, but quite bad if you want decent performance or economy. you need to chase down the spout connector, and confirm that the jumper is in place, and either find a jumper and install it or clean up the contacts on the one you have, so the pcm will sense it.

the 77 is most likely operator error during the test.

the lean on front bank is either due to a bad 02 sensor or a vacuum leak, or both. I would start by looking for vacuum leaks, but I suspect you need to change the 02 sensor. I recommend doing both of them while you are at it.

then, reset the codes and drive it for a while and see if you get any new codes.

 

[SHO n OFF]

Gonna start checking everything with a friend tomorrow.

Odd thing is, on the way home from work (about an hour ago), it ran perfectly. The engine light still pops up when the car is up to temp.

If the ect is bad, that would cause the pcm to cut back fuel, correct?


BTW- the backfiring you can only hear from up front when it does it, not out of the rear.

 

[rubydist]

on the contrary, when the pcm thinks the engine is cold, it runs in a more rich mode for the warm-up period. The warm-up mode times out after 20 minutes even if the ect still says the engine is cold, but 20 minutes is a long time to be running rich...