Misfire problem...need some opinions

[Meisner]

About 2 weeks ago, I washed my engine and afterwhich, I had a misfire at around 3-4000RPM. Ok, I got water somewhere I shouldn't have. After driving it about 100 miles, it went away. Good.

Today, out of the clear blue, it decided to start doing it again. I have not had the hood open for the longest time. It seems to occur right around 4100 RPM, at about 70% throttle and about 8psi (as measured on my S-AFC). These numbers seems very consistent. The engine is under load when it happens. If I'm on the freeway and work up to 4100rpm, it does not happen.

One other point, after I pass 4100RPM, it's fine. I went all the way to 5800 today and it was very happy...no misfiring. This is not a simple fuel pressure problem or something like that.

I tried resetting the ECU...no change.

Tomorrow I am going to dig deeper. I want to drive it some more and see if I can get some codes from the OBD-II port.

I have an S-AFC, but it is running bypass right now. Once I get on the dyno again, I will tune it.

The engine details:
- '96 5S-FE with a turbo charger, MR2 MAP and Supra injectors
- Walbro fuel pump (maybe 5K miles on it)
- Aeromotive FPR (again, about 5K miles on it)
- Ferrea oversized valves, valve job p&p'd head (5k miles ago)
- Stock ECU
- Magnecor wires (about 25K miles on them)


Anyone ever see anything like this before???

Thanks,
Steve

[TRDragoon]

have you checked your dizzy???.....i think 5s-Fe came with dizzy...

other thing is, there could be water /moisture in your sparl plug wire....but i guess it would't be a moisture problem since you washed the engine 2 weeks ago...

i guess i would look thru all the ignition componants first..spark plug, wire, coil. dizzy, etc etc

[Tony the Tiger]

Hey Steve, have you pulled out the plug wires from the distributor cap? I have had this type of misfiring problem with my Integra once, and it happened to be corrosion at the spark plug wire and distributor contacts. Sometimes you can't see the corrosion on the wire contact itself, but if you look deeply inside the distributor cap instead, you might find traces of corrosion which can cause misfires at mid RPM's. Most of the time, corrosion will not be enough to restrict voltage if you go heavy on the throttle (full load on ignition system), but it is enough to cause hiccups at lighter loads and higher RPM's

[Meisner]

No, since the sun has gone down I haven't been back out to the car. It's too damn cold out there and my Fiero is taking up the garage!! I hate winter!

In the morning I will definitely pull the wires. In fact, I have a new set of Vitek wires. I can try those to see if they make a difference.

Thanks for the thoughts guys. I'll let you know what I find.

[Fresco Bob]

fiero gets the garage instead of turbo camry?

[Meisner]

No, no, no!!! Let's get this straight. The Camry is always in the garage, but the Fiero has got a list of problems I am working on.

This is all in preparation for getting an MR2. I figure if I can rebuild a Fiero, working on a 2 will be easier. But the Fiero is cheaper to own...when it's running!

[shook]

Hey Steve i was wondering about your Apexi S-AFC.. you use the Prs meter on it as a boost gauge ? if so, is it accurate ? i know its in bars and im wondering because im using mine as a boost gauge as well but wondering how accurate it is compared to getting a seperate boost gauge. Btw my brother said you should check your wires and cap.. sometimes if its old and youre washing your engine water can leak in.

-shook

[jpimport.org]

Check your dizzy, remove your spark plugs and check for water.

[Meisner]

Originally posted by shook
Hey Steve i was wondering about your Apexi S-AFC.. you use the Prs meter on it as a boost gauge ? if so, is it accurate ? i know its in bars and im wondering because im using mine as a boost gauge as well but wondering how accurate it is compared to getting a seperate boost gauge. Btw my brother said you should check your wires and cap.. sometimes if its old and youre washing your engine water can leak in.

-shook

OK, I guess it's pretty unanamous...check the wires at the dist cap for water!

I have a separate boost gauge...much easier to read and faster to respond. I find the s-afc a little tough to read but I have measured it a bunch of times and it is very accurate. Always seems to match the mechanical boost gauge.

[shook]

Cool Steve, thanks for the reply i guess ill just continue to use my S-AFC2 as a boost gauge.. ive come to get used to reading it.. kinda just memorized my calculations to the readings


-shook

[Meisner]

Well, believe it or not, the problem is still there. I have pulled and regapped the plugs (they looked fine but the gap was a little big), measured resistance on the wires (5 - 6 k ohm on all, including coil wire), replaced dist cap & rotor.

After a bunch of reading, it seems like it could also be:
1. The coil
2. The igniter module
3. EGR valve
4. Low cylinder compression
5. Worn camshaft
6. Lean AFR

I am leaning toward #1 or #2, I have 110,000 miles on the first three components. I think #4, 5 and 6 would still cause the problem even past 4100RPM.

Any thoughts???

[Deuce]

my money's on the distributor coil

[Meisner]

OK...I got a new coil and was going to install it last night. Before swapping them, I tried to make the misfire happen to be sure I actually fixed the problem. It won't happen anymore...and I didn't swap the coils!

I don't really know what's going on!