94 S-10 - Misfire

I have a '94 S-10 that I recently put a used engine into. It is a 4.3

The truck has been running fine for since June, with the exception of the SES light comes on after a while driving it, but it is a low voltage reading from the O2 sensor. It doesnt cause any problems, so I havent worried about replacing it yet.


Well last week I took it for a drive and everything was running fine, and then all of a sudden it missed one time, and then started spitting and sputtering. It used over a 1/4 of a tank of gas just to go about 5 miles. I parked it, and checked the plugs (about 4000 miles old) and they were as black as they could be. So I changed the plugs, plug wires and cap-rotor (as it needed it anyway) and took it for a drive. It seemed to run perfect. However I noticed the SES light just stayed on at this point, rather than just comming on and off while driving.

I later took the truck for about a 20 mile ride on the expressway, and it was running smooth until I went to decellerate and all of a sudden it started missing again, and spitting and sputtering. This would happing intermitentlly, and then would go back to running good. It would latter just start missing about every 5-10 seconds while driving. I noticed it more when the engine was under more of a load or driving at higher speeds.

I checked the code readings, and this time it is showing an error check to the Electronic Spark Control. The wierd thing is, before I changed the engine out earlier this year, the last engine was doing the same exact thing. I'm wondering if it is a problem with the computer, since from what I have found the ESC is located inside the computer and can not be bought separate.

Any suggestions on what I should do?

Are you using the old distributor?
You may have a bad ignition module or some chaffed wires between the dist and the ECM.

Are you using the old distributor?
You may have a bad ignition module or some chaffed wires between the dist and the ECM.


It's not the distributor that was in the old engine, but it is the one that was in the used engine I put in it. It had about 80K miles on it.

I will check the wires on it, and see if I can see any signs of chaffing. How can I find out if it has a bad ignition module?

Well I checked the wires, and did not see any signs of chaffing.


I drove the truck last night, and it was running horrible. It almost acts as if it is getting bogged down. I can floor it, and it will take a second to clear it out, but will accelerate without missing. I almost want to think it is flooding it out.

I idled with it for about 30 minutes and then shut it off for about another 30 minutes, then took it for a local drive. It drove perfect without a hitch. I then turned it off, and parked it for about 45 minutes and took it back on the expressway, and again it drove without a hitch for about 10 miles then had a few hiccups, but nothing like it was doing. About 5 miles down the road it started to do it more frequently, but still not as bad as when I first took it out that day.


It's really got me baffled, and eventhough I always do the repairs myself, I almost think I need to take it to someone, but I really don't know who or even how to make sure I'm not getting took on it....

Did you transfer any parts from your old engine to the one you installed...like the coil
Also what is the 8th digit of your serial number...W or Z?

Did you transfer any parts from your old engine to the one you installed...like the coil
Also what is the 8th digit of your serial number...W or Z?


Nope, I didn't transfer any mechanical or electrical parts to the one I installed.

It is a "Z" engine.

Oh Yea, I forgot to mention, here are the following codes the SES is giving:

12
13
15
43

13 open o2 sensor circuit
15 high temp sensor voltage
43 knock sensor
The one that I would check first is the 15. This code states that the ECM is reading a coolant temp of -30 degrees. If the ECM reads a cold engine, it will add fuel to assist with cold start and cold engine driveability until the engine warms up.
If the engine is at operating temp (195 or greater) and the temp sensor is telling the ECM that the engine is still -30, you will experiance some major driveability issues.
13 states that there is an open between the O2 sensor and the ECM. This is also part of fuel control.

So when the O2 reads an open, does that generally mean it is bad or that maybe the wire has been cut?

Is there anyway to test an O2 sensor?

The O2 sensor creates an AC voltage when it heats up.
If you disconnect the sensor connector and install a multimeter to the sensor and ground, you should get a varying voltage between .1v and 1v. If the voltage varies...it should toggle between those to voltages with a midpoint being .45v...that the sensor is good and I would check the wiring to the ECM for opens.

Actually, the O2 sensor creates a DC voltage. It goes from .1-.9 volts, following fuel. Although the O2 sensor reads the O2 in the exhaust, the voltage follows the fuel. The richer the mixture, the higher the voltage. This suggests a method of testing. By enriching the mixture, by for example disconnecting the map sensor, the voltage should rise to .8-.9 volts. Replace if it does not. This assumes that the disconnect created a rich mixture. The temp sensor reading -30 deg should be addressed first. The rough idle could also be caused by a sticking EGR valve. This will also create the black plugs due to misfire. Some food for thought. Address the temp sensor's reading first. Ray

if you are getting spark knock your plugs are not firing at the right time, check your base timing....are all the plugs fouling or just one? a fouled plug may run fine at idle but once you put it under load the compression goes up and it makes it harder for the plugs to fire. and how are your spark plugs fouling? oil, carbon, ect. your valves might be leaking oil into the cylinder causing your plugs to foul out, witch would in turn cause the misfiring hope it helps

Is this a Vin z or Vin w?

I have a 94 S-10 4x4 w/ 4.3 vortec CPI - 143,000 mi. The engine starts fine when cold.
After a short warm up, the engine would start to Skip and Misfire, Real bad under load and when hot.
EGR Valve was Clean. Found a bad Ignition Coil. $15.99 @ Auto Zone

Ummm..

so the coil fixed it?

Yes, actually made it Driveable but about 2 weeks later, it will develop a skip or stumble while driving City/ Highway and I have replaced the Ignition Module in the Distributor and still not 100%. Can the pickup in the Distributor be bad. It does not have the EGR/ Carbon symptoms - I know when that happens - Stalling, Rough Idle. I also had the CPI replaced at about 125,000 mi and now have 144,oo mi.
Any help ???
Timmy from Connecticut

code 12= no engine rpm reference pulse - system normal
code 13= oxygen sensor (o2s) circuit open - left side on 2 sensor system
code 15= engine coolant temp (ect) sensor - circuit low or open circuit
code 43= knock sensor (ks) or electronic spark control (esc) circuit fault

fyi, when getting a motor fron the junk yard you should replace all gaskets and seal before using them, you may have gotten one with a weak or blown head gasket