Engine spitting up and back firing

[wonderingmind]

I didn’t know exactly where to place this question so hopefully under engines will do if in the wrong place sorry.
I recently did a v8 swap with my s10 I put a 90 model tbi 350 in my previous 4.3 tbi 89 s10. I run it down the road a few times after I got it running with open headers with no problems no more then 2miles at a time though..(you know how a kid is with a new toy I just couldn’t wait.) Went today and had dual exhaust put on with two Dynaflow mufflers (which sounds alsome) they put the old 02 sensor in line with one side. (so it’s reading off of 4 cylinders) got it back drove it around town a few miles with no problems. Was taken it home which is about 15miles about 5miles in I was sitting at a read light and took off and it started back firing and spiting up like the timing was way off. I hit the on ramp of the interstate and the motor wouldn’t even get up to speed just backing firing. I have a air/fuel ratio meter and it was reading way rich. All other gauges where good oil, alt, and temp. I pulled over thinking a spark plug wire might have come off but ever thing looked good tried again with same results. I got the wild hair to unplug the timing advance thingy (you know tan wire with black strip you unplug when you set the timing.) After I unplugged that it ran like a champ. After making it home and double checking everything I reset the computer by disconnecting battery and plugged the timing advance back up run it down the road after about 5miles same problem unplugged timing advance and ran fine. Has any one ever run into this?
I’m wondering about the o2 sensor with it only reading one bank will it cause this? I don’t think it would be plug wires, cap or button b/c it runs good with timing advance unplugged. The o2 is the old one from the 4.3 ran fine with it. Anyone have any ideas they can point me in the right direction.
Sorry for the long winded story but want everyone to know what I’m running and a good description of the symptoms.

[ZR1BLAZER]

yes. its your knock sensor. you are getting into "LIMP HOME MODE" the ecm is retarding the timing and letting it run rich so you dont burn anything up. a safety precaution programmed into the ecm. you mention when you unhook the timing jumper line it runs great. which means the ecm cant retard the timing now. what color is the top plug on the knock sensor and is you check engine light on? need to read some codes and go from there.

[HATFIELDSCHEVY]

you beat me there i was going to say same thing. and he's right scan data will verify real quick.

[wonderingmind]

I think it is a white top knock sensor. both the 4.3 and the 5.7 where the same so I used the 4.3 sensor. On the 4.3 motor the knock sensor what mounted right behind the drivers head right below the oil sending unit with the 5.7 I had to relocate it I moved it to the water port right at the motor mount. Where most are mounted on 5.7 except I put it on the drivers side.
I never seen the check engine light on with it acting up. Once I unplugged the timing advance wire then it sets the check engine light which I figured would be expected with the timing tab unplugged.
Do you know how to field test the wire to the knock sensor? Do you think it might be the wire, knock sensor, or location. Or should I ask with no check engine light on where do I start to test and fix the problem.
ZR1BLAZER thanks so much for the info I never would have though that knock sensor never crossed my mind but after you explain it it does make sense.

[wonderingmind]

is it safe to drive the truck with the timing advance wire unplugged for a day or 2 untill I figure out the problem? You know the kid and his new toy just wants to play.LOL

[-Deception-]

yes. its your knock sensor. you are getting into "LIMP HOME MODE" the ecm is retarding the timing and letting it run rich so you dont burn anything up. a safety precaution programmed into the ecm. you mention when you unhook the timing jumper line it runs great. which means the ecm cant retard the timing now. what color is the top plug on the knock sensor and is you check engine light on? need to read some codes and go from there.

I would guess that too.

[wonderingmind]

so the starting point to cure this problem would be where with no check engine light on.

[HATFIELDSCHEVY]

once the truck goes into closed loop op. the pcm uses eng data to control spark fuel timming ect the great sounding headers and dynaflos can set up a reonance to cause the knock sensor to reverbarate and retard timming. the switch thou a single wire switch must be grounded. on performance eng. i will isolate the knock sensor if you want you can mount to the fire wall drill a hole 2 rubber washers and a ground wire loop with a nut on the back of it.no check eng light on the sensor is working and doing its job remember we are gussing by symtom the best way to check is to hook to a scanner and veryify before you do anything.

[wonderingmind]

I have a spare knock sensor I will give this a try. Thanks again for the info.

[spacecadet]

1st does the ck engine light work? I have to ask because I have seen too many times the light doesn't 'bulb check' when the ignition is turned on.
More than likley the check engine light isn't on becasue the computer can't verify there is a problem. The pre-96's OBD 1 isnt as 'smart' as the OBD2 is in the 96 and newer cars. To set a light in an older ride there has to be a major malfunction.

[ZR1BLAZER]

code 42,43 knock sensor ignition timing will set a code right away ecspecually if your in limp home mode. check those codes before you do anything. and a new sensor is only $30 from auto zone. if it comes down to it buy a new one. but hatfieldschevy is right. a loud exhaust system can throw off a knock sensor.

[HATFIELDSCHEVY]

the way the ecm check knock single. at idle it should receive a single if no noise it set a low voltage code. then after car reaches 203 degrease and high load it will advance and look for noise.it only does this once per key cycle. if these conditions are not met it will not set light.if these conditions are met it is working and will not set a code

[Melonhead]

Wait a minute! Why would the an engine run great at 0* timing. If you are driving and speeding up, you are not at 0* timing. DID you set the timing to 0* with the jumper disconnected???? Seems odd that there would be any performance with 0* of timing????? This would also explain no codes. The computer is trying to make up the difference. This is what I would do. Check you timing first since it is free. The is the seting was correct and the problem persist, change the Knock sensor and check your check engine light.

[wonderingmind]

yes the light works. The check engine light will come on when you unplug the timing advance that sets the check engine light.

[wonderingmind]

I had a spare knock sensor from the other motor both being white tops single wire. I hooked it up set it on the off to the side of the motor took a wire and clamped it on the threads with a hose clamp and clipped the other end to a good ground. Think this is how it was talked about hooking it up.
Took the truck down the road and still have the same problems. Starts spitting and back firing fuel/air ratio meter shows rich motor has no response to any throttle position I pulled over to the side of the road and the fuel/air meter show it going back down towards lean I give it some gas and the motor responds until I see the fuel/air meter jump back up to rich and it starts back firing again. No check engine light on during all this. Unplug timing advance tab and check engine light comes and stays on but motor runs out.
Could I have rigged the knock sensor up wrong of is it something else?

[wonderingmind]

just doubled checked the timing and seems to be right there at 0deg. I am setting and checking the timing with the timing advance tab unplugged.

[Melonhead]

The only other thing I can think of is Vacuum. Is all the vacuum lines ran where they should be? Did you check the amount of vacuum present while idleing?

[wonderingmind]

All of the vacuum lines are hooked up; there was one on the back of the throttle body I wasn’t sure about. I could have crossed two vacuum lines. I think there are 5 vacuum ports on the throttle body. One was already capped of that only left 4. Ones the PVC can’t really mix that one up that leaves 3. 2on the front and the 1 on the back...
I don’t have a vacuum gauge to check the vacuum on the motor. I might have to borrow one from my brother to check it.
Is there any chance if I left one of the 4.3 electric components on that motor could it cause any of this? You know like spark control or something like that. (I know the spark control was off the 5.7) but just a though. Can the electric pick up have a clitch in it? Think that’s what it’s called (loc. On the distributor under the cap that the wires from the coil and wiring harness plug in)

[Jimmybeam]

The vacuum port on the back of the TBI is for the MAP sensor. The other two open on the front should go to your EGR and the fuel canister I believe.

[wonderingmind]

well that's how I have it hooked up guess that rules that out.

[Melonhead]

You already know we are trying to throw any possible item at you to check. My next sugession is to check the timing while the advance is plugged in. See where it is and what the computer is doing. While the timing light is there. Rev the engine to see if the timing is moving to respond to the engine. Unplug the map and have someone cover the vacuum port. See if the timming changes with the map having no vacuum. The timing should go up. This will at least rule out the computer intereacting with the load of the engine. Check your plug wires for them being install in the correct firing order.

[wonderingmind]

Do you know or is there a set timing is should be at with the timing advance plugged up?

[Melonhead]

At idle, the motor should be running between 10 and 18 depending on the load and the idle speed. This is best seen with an advance knob timing light. The things you are looking for is what changes or doesn't

[wonderingmind]

Well got home a little early today to work on my truck. I borrowed my brothers snap-on scanner and only code was like 42 which is where I unplugged the timing advance tab. All sensors seemed to be within limits.
So I went with my brothers idea and stuck the timing light on the coil wire and work down to each plug to check for a skip. Well while it was on the coil wire I was able to get the truck to act up and sure enough the light would stop blinking for a split sec. So I found the coil that was on the donor truck with the 350 stuck it on run it down the road a little ways with no problems. (Boy was I happy) about that time my wife made it home so she and I jumped in to take her for her first ride in it.  Well made it less then 3miles from the house and started spitting up again and the motor died. Pulled over and I be darn if it wouldn’t crank. So here we sit on the side of the road less then 3miles from the house I’m trying to figure out how I’m going to get this POS home. (Can you tell I was pissed) I was able to get a buddy to help me tow it home. We went to push the truck out in the road so I could get a tow strap on it and tow it as we was pushing I started turning the steering wheel and what do you know more bad luck something popped in the steering column and I lost all steering. With my luck I’m sure I broke the clock spring in there also. (If it wasn’t for bad luck I wouldn’t have any luck). So what should have taken 15 minutes to do took 3 hours. I’m at the point to start smoking well smoking with a busted metal gas line. LOL Anyone know how much insurance will give me for a toasted 89 s-10? I guess the only good news is there was no spark so I’m narrowing it down. Anyone else have day that you shouldn’t have gotten out of bed?

[HardinValleyMagic]

Hope it turns out to be 2 faulty coils. That would be very strange but you never know. Also check to make sure all connections are good with the wire. Something might be shorting out.
Just some random thoughts. Hope you find the grimlin soon before the fire dept. gets a call from neighbors. LOL!

[Melonhead]

Pull the ESC module and have it tested. It may have been weak and finally went out. Sorry to hear about your day and the steering.

[wonderingmind]

I am the fire dept... I was wondering about the modules in the distributor.? When they go out dosen't it quite firing? I'll have to get my test light out to see if the coils are getten juice.

Just got a pic up of my s-10 as my icon. What do you think? In the process of getten a few pics on-line so you guys can see with what I'm working with.

[-Deception-]

The ignition control module in the distributor controls the pulses of the injectors (i know i had mine go out and after replaceing every other fuel part I found that out) Also im on the fire dept. too Im a EMT, Hazmat Tech, High and Low Angel Rescue, Advanced Extrication, Fire One, and Confined Space and some others but its alot of fun.

[wonderingmind]

What about the pick-up module? Yea that's where I was at today I'm in paramedic class I left early to work on my truck. Boy was that the wrong move. You paid or volunteer? You EMT-B or Emt-I? I like about 2 more months before I finish my medic class I'll be so glad that's over. I think all firefighter love the rush running in a burning building no feeling quite like it. Dive rescue is a blast too if you have that there and it's not to cold. Our class went to Florida twice for dives.

[wonderingmind]

I also put some pics of my truck in my album also a pic. of the fan shroud I made and powder coated yall tell me what you think. The 2 10" puller fans work great that is when the trucks running. LOL
I'm running 2 10" puller fans with the jegs wiring kit with 185 deg temp. sensor and a 165 deg thromostat.

[Melonhead]

The pick up coil and driver is under the rotor and weights. The ESC has different things it controls. The pick up acts as a crank trigger.

[HATFIELDSCHEVY]

looks good. the pick up coil in the dist can go bad and if it has a loose dist shaft will cause drivability issues. when they go bad altogether it will quit. easy to check unplug from module and put an ohm meter on the leads when you crank should see the magnetic pulse. the module then transforms the analog single from the pick up to a digital single one for the coil one for the pcm for injector pulse, the pcm then grounds the injector. a lot of parts stores have module testers in house so you don't have to just buy one they can load yours down and check for failure. hopefully it is just the coil. i had a cheap summit tach hooked up to my truck that would short out my coil.

[wonderingmind]

UPDATE: After my truck broke down the other day I went today and took the module off and went to the local parts store and had it tested. The module tested bad so I went ahead and got a module and a pick-up. Figured I might as well replace them both. Plus the pick-up connecter was pretty rough looking. But it all on an thank god it crank up and seemed to run well let it run for 30mins or so with not problems.
When the adapter broke in the steering shaft it broke the horn button also so I bough another grant steering wheel installment kit and horn button just have to wait to borrow the tool to install it all. So I can try my luck again and drive it down the road and hopes that all goes well. Keep your fingers crossed.
What’s weird to me is that I’ve never seen a module act up like it was before going out. Been burned before on a multi-port skipping and sputtering and it ended up being the coil. I just hope the module was the problem and that fixes it and not just some fluke thing that just happen to go out leaving me with two problems. I will find out in a day or two when I get the steering wheel back on and take it down the road.
Thanks again for all your help and I will keep you informed weather that fixes it or not.

[HardinValleyMagic]

Glad to hear that! Freaky as at was, hopefully that fixes it.