Going on 2 years with this sl1, have changed alot of stuff after the previous owner failed to maintain, it has been good to me until now which sits at 144,xxx mi.

With a warm engine, ill get some random miss-fire/hesitation that gets worse with load, going up-hill seems to get the worst of it. Sometimes it will climb hills no problem, most other times it will not, if i simply back off the throttle and press it again lightly it can sometimes help, sometimes it doesn't.

This normally occurs right around 1500-3000 rpm, but have had the same thing happen at 4000+ after a downshift to try and fight a hill with a hesitating engine, you get 100% power and back to 50% and it just fluctuates back and forth. I did this once and found the ses light flashed for 10 seconds while fighting up the hill, did not want to damage my valves/cat so i never did that again.

When warm, the hesitation under load will happen probably 7 out of 10 times, seems to be related to how much i open the throttle and will have me always second guessing if i can even make it up a hill without a hard and severe downshift that flashes the SES light.

Things i have changed last year

OEM plug cables (broke the last set by not using anti-sieze)
NGK bkr11/.040 plugs
Both ignition coils
map sensor
Radiator fan
Thermostat
Intake air idle valve
cleaned egr

Things i have changed two years ago.

Coolant temp sensor (brass style)
Intake temp sensor (brass style)
Upper radiator hose
Alternator
Oem plug cables
starter
Throttle position sensor

I have a few things suspected but would like to hear all your thoughts before diving into test/conclusions, i have checked for stored/pending and historic codes and all come back with nothing stored.

1. I may have a faulty ignition coil/wires/plugs and/or a faulty ignition coil module. (I've heard aftermarket ones dont last long)

2. I may have a clogged cat. (There is a minor rattle near the area)

3. I may have a dirty fuel line/filter ( have not changed fuel filter or pump yet but have used fuel cleaner a few times to be safe)

let me know what you guys think, id hate to go touching random things on this car as its not near the most robust thing I've owned.


*edit - i pulled the plugs and cyl 2 shows a speck of detonation, cyl 3 was ash fouled.
I changed the plugs and double checked for a .040 gap, Have not test driven the car yet as its already late. I'll check tomorrow.

If it does not improve I'll have the fuel filter in mind.

 

Went for a drive and to my surprise i couldn't get it to buck/hesitate or missfire at any rpm, it seems like the plugs were bad.
They went about 10,xxx miles and had fouled from ash deposit, they also look pretty worn for its age. Im going to say the 20+ year old fuel system is a bit dirty and needs some TLC to prevent a repeating problem.

 

 

We're the fouled detonated plugs stock ngks or another type?

I would pull the plugs once in a while to see if the ash fouling is continuing.

You could also check the back pressure to confirm/deny cloggish cat.

 

The old plugs were 2 year old oem ngk's, for some reason the gap had expanded near the .050 mark. i did have a mediocre overheat last year and it could have had something to do with it.

i finally got a good drive today and all is well, can't believe how sensitive the ignition system is on these cars.

 

Good to hear.

Yeah the ignition system is finicky. People put iridium and superexoticum plugs in b c AutoZone says they are a cross match, then can't figure out why they have misfires that can't be easily isolated because they are intermittently everywhere.

If that plug really did start at 040, could have been some detonation going on

 

You do know that spark plugs DO NOT come pre-gapped, right? I don't know how many times I had to tell people to check the gap on the plugs before they installed them when I was selling car parts. Some didn't even have a clue, so if I wasn't busy, I'd look up the spec and gap them for them. Drove my managers ape**** crazy sometimes when I'd do that! LOL