Acceleration issue

[Markb873]

I have a 1993 s-10 Blazer 4wd. Normally I have a stumble with a light touch of the gas pedal and it has always had a rough idle. (in neutral the rpms wander) I live on 55mph roads and I noticed if I floor it up to speed once it will run excellent for the rest of the day. I can stop it and start it many times and it runs great. As soon as it sits overnight it's back to stumbling. I'm scratching my head on this one. All I can tell you is that it runs a bit smidge bit rich because of a small exhaust leak before the downstream 02 sensor. I checked the spider injector and replaced the plenum gasket with some improvement. No other vaccum leaks. New fuel filter, plugs, wires, cap/rotor, timing is ok.

Any Ideas?

-Mark

[MT-2500]

Any check engine lights or codes?

How is the fuel pressure?

Good AC -Delco plugs?

Good Hot blue spark to all plugs?

[b1lk1]

It does sound like it could be spark related since after you floor it it possibly cleans off the electrodes on the plugs and they are somewhat fouled. I would pull a few plugs just to see what they look like.

[Markb873]

Ok, I have no lights or codes. I checked everything over again and did find a burnt plug wire. I replaced the whole wireset again to be safe. Sparkplugs are new. My fuel pressure is good. My IAC was a bit out of wack...fixed now. The TPS tested perfect. I still have the rough idle and the stumbling with the light touch of the throttle although it is reduced.

Now I did borrow a known good plug from another vehicle and put it to rest on the block in the boot. I got a yellow spark with a intemittent hint of blue. In the Haynes book they have a check to do on the coil. It technically passed all the tests as they had outlined however, the resistance from the top right side terminal to the coil wire terminal that leads to the distributor (looking from the backside) was supposed to have a high but not infinity resistance. I had only 8 ohms. Haynes said replace if infinity. I'm wondering replace if low too?

My other question is this: Is the weak spark more pronounced at idle vs. high speed?

Thanks,

-Mark

[MT-2500]

Weak spark causes more miss under a load.
Weak ussually cause weak spark to more than on cylinders.

You also might check cap and rotor and dist shaft side play.
Good luck

[Markb873]

I had weak spark on all cylinders.

[MT-2500]

Always check for spark at coil tower to.

A good spark tester with adjustable gap helps on testing spark.

Your spark should have a loud snap with a good hot blue spark and jump close to a 1/2
If weak at coil there check the ign coil out good.
Good Luck

[534BC]

Can I understand the symptoms clearly?

It has a rough idle with rpm wandering.
It takes an application of WOT to eliminate symptom until it sets a long time.


Questions:
If left set to warm up at idle will the problem still be present?
If driven for hrs very easily without going WOT will problem still be present?
Do you think it is temp related? (cold engine is problem?)

[Markb873]

534BC,

The idle will be roughly the same but a bit better if it idles warm. If it's driven easy for about an hour it does run better but not as good as wot. It seems more moisture related as the tempreture doesn't have as much of an effect. On a slushy day back in March i somehow splashed the whole top of the engine with slush and the problem slowly developed after that. The engine died afterwards and wouldn't restart right away. It took about ten minutes. I assume water in the distributor?

-Mark

[534BC]

There's a good chance. I just fixed a very similar problem where we had a slight stumble upon take off at low rpm nd the truck had been driven for miles since the boy pressure washed it. We did some plug,wire,spark checking and after hearing that it had been pressure washed I removed the (coil in cap) cover to find standing water still in there. We blew it out good and dry and the trouble went away completey. I hope your fix could be that easy.