My daughter'* '97 3.1 Lumina has 90K and has been well taken car of by the previous grandmother who had it from its creation through the time my daughter has had it (the past five years).

Issue:
About three months ago, she noticed a bit of a very slow coolant loss, and the pump was found leaking. Replacing that, about a month ago, it started having a loss of power between 20-40 mph. I took the car and found misfire codes on cylinders 2, 4, 5, and 6. I cleaned the MAS, replaced the spark plugs and wires, checked all the coil-packs with a spark tester (they checked out with strong spark), and checked the fuel pressure at the fuel tube that feeds the injectors . With that done and the problem persisting (especially when the car warmed up to operating temp), I had Cottman transmission (very reputable guys at this local shop) and they checked it out and found the same engine codes, but stated the transmission was working fine. During the next few weeks, another noted very slow coolant leak was detected without anything leaving the engine. During this time, possibly unrelated, I had problem starting the car and found the battery had developed a bad cell, but the alternator checked out, so I replaced the battery. Anyway, knowing the 3.1'* storied issue with the complicated factory head gaskets leaking coolant, I took the large task and replaced the head gaskets and had new valves and seats installed in the heads. My daughter stated it is much better, but still noted she felt there was still a lack of power on the hills. She has borrowed my '01 Silverado and she has power to spare and stated that maybe the truck has spoiled her on power, but I don't think that is going to be the issue at all.

I'm getting the car this evening, and need to go back to square one on what could be the issue. I wanted to see if anyone else might be of assistance in a potential issue. These are the fun ones 'eh?

Could it be the control unit for the coils? A fuel injector control issue? IDK.

Thanks so much in advance for any assistance!

Dave

Could it be the ECM?

EGR?

I have no codes from the above, but...

CAT?

...still no sensor codes on the exhaust.

I took it for a test drive and here'* what she did:
1) Starting it, it had a slightly rough idle but moved easily at low speeds.
2) Upon pulling out of the neighborhood and onto a State road that headed uphill, I pressed the accelerator about 1/2 way as typical. Initially it accelerated as expected, but after about 30 yards it started to run at a lower speed and engine rev as if I reduced the pedal to about 1/4.
3) When the car reached the crest of the hill, even though I didn't alter the pedal position, it began accelerating to a more expected 1/2 pedal acceleration.
4) The above was typical on all uphill slopes.

5) Noting the engine service light was on, I had the code pulled and received the following: PO301 "cylinder misfire detected - cylinder number 1"
6) I pulled the #1 wire (wires and plugs are new) and did a spark test, it was sparking strong and quickly at a separation of 36-38.

I'm going to pull the plug and check it for damage, but that is an extremely remote issue. I don't even understand why 1 cylinder misfire would cause the acceleration issue that she has, it just does't add up. Previously, before the heads were pulled, the misfire codes were intermittent misfire in cylinders 2, 4, 5, and 6.

Ideas? Thanks again in advance to any assistance.

Look at the short term trims if they start climbing during the event you may have a weak fuel pump or plugged filter.

What is the fuel pressure key on engine off?

What is the fuel pressure at idle?

I cannot find the piece of paper I used to scribble it down before I changed the head gaskets (like a dummy I probably threw it away as if it were trash), but I'm pretty sure it was: 42 when the key was in the on position, and somewhere around 38 when it was running.

Can you expand on this, I don't understand what you're stating in regards to "trims."

Oh, and as a note I forgot, yesterday when I was test driving her again, and walked around the car towards the rear, I could smell what seemed to be a little un-burnt fuel.