Slight Regular Misfire and No Power After Upgrades (Page 1/6)
Notorio JUL 11, 03:47 PM
Background: you may recall that the success of my '88 2.8L, 2-year long rebuild (including port&polish heads, port exhaust logs, port intakes, 1.6 rockers, Fiero Store valves, and Rodney Power Pulley, cleaned/tested fuel injectors, etc.) was sullied by briefly connecting the ground wires near the starter to HOT which melted a few wires in my harness. After repairing the harness the car started but ran poorly due to water in the gas. After flushing and 2 tanks of fresh gas with IsoHeet the car runs well except for two lingering issues which I have been loath to address:

1) Dash Temp Gauge slowly goes off scale during warm-up.
2) Engine idles well but SEEMS to have a slight misfire and no power.

THIS POST is only asking for ideas on #2, the Idle/Power problem. I started another thread for problem #1 because I feel that they are not related.

Data

a) When I first started the car it barely ran with significant misfires and buckets of water coming out of the exhaust. As noted this declined in severity to where the idle seems normal to me, but in doing a slow throttle increase I detect a slight, regular-periodic misfire (i.e. not random). I've driven the car several hundred miles now but it stopped improving.

b) I did a propane 'leak test' all around the hoses and fittings and detected no idle increase so I think there are no vacuum leaks.

c) Before the rebuild/upgrade the acceleration was at the so-so level that seemed consistent with my prior Fieros but now it seems even less peppy, never giving that 'pull' feeling it used to show a bit in 2nd or 3rd gear.


I'm at a loss of where to start diagnosing this or even validating that something 'is wrong.' I'm not 100% sure there is actually a misfire. One other thing, I've kept my registration current but I really shouldn't drive it with expired plates. A smog test is needed and I'm worried to go get one and find I now have a 'gross polluter' on my hands.
pmbrunelle JUL 11, 06:29 PM
Is your ignition timing good?

If the harmonic balancer slipped, then you would be timing the engine using incorrect reference marks, resulting in incorrect timing.

Did you use a refurbished harmonic balancer on the rebuild?
Notorio JUL 11, 07:29 PM

quote
Originally posted by pmbrunelle:

Is your ignition timing good?

If the harmonic balancer slipped, then you would be timing the engine using incorrect reference marks, resulting in incorrect timing.

Did you use a refurbished harmonic balancer on the rebuild?



Hmmmn, well I was able to set the timing using the cylinders 1 (and 4?, whatever the right one is). But I did reuse my old balancer with the old marks.
pmbrunelle JUL 11, 07:52 PM
And did the rubber look good or deteriorated?

If the rubber had deteriorated, then the exterior ring of the balancer could have slipped.

What if, without the paperclip-in-the-ALDL, you simply rotate the distributor to find the strongest idle?

[This message has been edited by pmbrunelle (edited 07-11-2020).]

Notorio JUL 12, 07:49 PM
Well, it certainly didn't look like a newer balancer but I'll check it more closely this week and try the distributor experiment you suggested.
Notorio JUL 20, 12:49 AM
Additional Data:

1) I warmed up the car in pretty much pitch dark conditions and looked at the ignition wires and boots. No evidence of arcing to ground. This seems like a good result however I have never had occasion to see arcing in the past so I don't even know if it is visible.

2) I then tried the experiment of rotating the distributor while NOT putting in the clip. The position adopted from my prior timing job ran the best. Advanced a bit and it started to misfire at idle (normally I only hear the misfire at higher revs) and retarded a bit, same story. I don't really understand what this did except prove the correctly set timing ran the best at idle.

Any thoughts?
Patrick JUL 20, 01:10 AM

Have you checked each spark plug wire for resistance to see if they are all within spec?
Notorio JUL 21, 12:28 AM

quote
Originally posted by Patrick:

Have you checked each spark plug wire for resistance to see if they are all within spec?



Ah hah! So in doing this just now I found that 5 of the 6 wires were in the range of 7.6 - 8.5 kohms. For the 6th wire the plug boot came off but the clip remained on the plug and the conductor was left flapping in the breeze. I'm tempted to declare victory, unless I have merely destroyed a wire that was otherwise OK. In any event, I just ordered the Fiero Store wire set and will see what-is-what after they arrive. In the meantime I can go to sleep now nursing the hope that 'this was the problem.'

[This message has been edited by Notorio (edited 07-21-2020).]

Patrick JUL 21, 01:27 AM

Don't take any short cuts. Now that you have the wires disconnected from the spark plugs, remove all the plugs and check to see if one (or more) look different than the rest. Should all be the same color. Also re-check the gaps.
pmbrunelle JUL 22, 12:04 AM

quote
Originally posted by Notorio:
I don't really understand what this did except prove the correctly set timing ran the best at idle.



That was the point of the test, to confirm that the timing was set correctly... to exclude the possibility of incorrectly set timing.

The spark plugs themselves also have a resistor between the post and the centre electrode, so you can check those too.

[This message has been edited by pmbrunelle (edited 07-22-2020).]