4.3 TBI cranking issues

YJJPWrangler

YJJPWrangler

Well-Known Member
Joined
Jul 19, 2005
Location
Charlotte
91 4.3 TBI out of a S10 Blazer. I have good spark, good fuel but it will not run. Timing is set to 0 degrees(second mark on the crankshaft) . I have disconnected the timing advance wire. Fuel pump is rated at 20psi. I am getting a good cone of fuel into both injectors with some pulse/modulation. I pulled off the fuel pressure regulator last night and will replace it as it didn't look all that great. I am getting some fire back in the manifold. I can also disconnect both injectors after cranking for a bit and the motor will stumble/want to crank off the gas still left in the intake. @R Q has suggested a new MAF. Any other ideas?
 
If it has fuel, fire, compression, and it's in time, the CTS followed by the map are the usual suspects as either one will cause it to be very lean or flooded. Once I saw a bad one wire o2 sensor do it, but that's highly unlikely.

Also check the fuel pressure and volume. If its low it'll spray gas but not enough to run.

Make sure the spark is at the plugs, not just the coils to rule out a cap or rotor issue.

I'll try to post up the test procedures for the map and cts later if no one beats me to it.
 
@Tim C I verified all six spark plugs have fire at the plugs themselves.

Fuel pressure/volume - the original pump I had was a carter P5000 that was recommended by many on Pirate. That pump is rated to 75psi. During cranking, it would dump fuel in with no pulse or modulation and would immediately flood the motor, like gas dripping from the exhaust flooded. I switched it last night to an airtex E8153 that flows at 20psi. I am now getting some pulse/modulation but still feels like its dumping way too much fuel. I am planning on installing a new fuel regulator today.

I can't remember if I installed a new CTS or not(the sensor on the front of the motor near the thermostat) or a new MAP.

There is a single wire O2 sensor that is hooked up that came with the junkyard exhaust Y pipe I sourced, it is hooked up.
 
Are you sure the timing is not 180* off?
 
The fuel pump won't cause flooding unless the regulator is bad or the return line is pinched. I run a e2000 pump on my TBI which is a 40 psi multi port injection Ford bronco pump. It runs just fine. You can verify by teeing into the pressure line anywhere between the pump and throttle body. Even remove the fuel filter and use rubber hoses and clamps if necessary. And an old oil pressure gauge or air compressor gauge can be used. If it's higher than 15 psi with a stock regulator or computer tune you need to diagnose that first. If it's less than 9 that's bad too.
 
Is this the same one you chased all over before? Did it ever run right? I can't remember.
 
Tim C said:
Is this the same one you chased all over before? Did it ever run right? I can't remember.
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Same one, never really ran right but it did "run" backfired intermittently. That last issue was a case of no spark that you helped me with.

@Jeff B I'm pretty sure the timing is not 180* off. I brought it up to TDC on piston 1 and felt compression through the spark plug hole. I'm going to re-verify that I'm at TDC at 0* by taking the valve cover off and watching the rocker arms move. The front two rocker arms should be closed at TDC for the compression stroke if I remember correctly.
 
Reason I asked is because I was wondering what had been changed between then and now. If the distributor hasn't been out the timing shouldn't have changed for example.

If no major components have been messed with then it could be a sensor issue.
 
It never ran right the first time. I was getting fireballs out of the headers and it was chugging too.
 
My only experience with a 4.3 was in a buddy’s crawler that NEVER ran right. We got it to run *marginally* better buy adding a spacer on the crank sensor up front my the harmonic balancer. It always had a hesitation and stumbled, specially if you needed to back up and bump something. It would fall on its face, then go but that killed the whole “back up and bump it”. He eventually done an LS swap.

As for yours, my immediate thought was 180* out on the distributor. Also, are you 100% sure that the plug wires are hooked up right. Always double check the obvious as they get overlooked the easiest. I can’t offer any help on the fuel, except it does sound like it’s out of time and and maybe you do have the right amount of fuel but it just seems like a lot since the plugs are firing at the wrong time?
 
Also, I’ll tell on myself here with an embarrassing situation. Surely you haven’t done this but just to cover the Uber simple things...

I once rebuilt a 351M in a Bronco for a friend. When I put the motor back together read to bring the #1 cylinder to TDC and make sure that’s where the distributor was pointed. Well, stupid 20 year old me took that super literal and I literally set the distributor pointing AT the cylinder, not the point for cylinder #1. It actually ran, but very very poorly. Even drove it like that a short distance till another buddy figured out why it ran so bad. It was wayyy off time and needless to say I felt real dumb.
 
77GreenMachine said:
My only experience with a 4.3 was in a buddy’s crawler that NEVER ran right. We got it to run *marginally* better buy adding a spacer on the crank sensor up front my the harmonic balancer. It always had a hesitation and stumbled, specially if you needed to back up and bump something. It would fall on its face, then go but that killed the whole “back up and bump it”. He eventually done an LS swap.
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@YJJPWrangler see, simple solution. :lol:
 
Years ago I rebuilt an engine and had a very similar issue, checked and double checked everything. Finally, found the coolant temp. sensor could be snapped in 180 deg. out.

Pulled the plug, flipped it 180 (only 2 poles) and it fired up and ran great.
 
77GreenMachine said:
Also, I’ll tell on myself here with an embarrassing situation. Surely you haven’t done this but just to cover the Uber simple things...

I once rebuilt a 351M in a Bronco for a friend. When I put the motor back together read to bring the #1 cylinder to TDC and make sure that’s where the distributor was pointed. Well, stupid 20 year old me took that super literal and I literally set the distributor pointing AT the cylinder, not the point for cylinder #1. It actually ran, but very very poorly. Even drove it like that a short distance till another buddy figured out why it ran so bad. It was wayyy off time and needless to say I felt real dumb.
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:lol:. I haven't done that, my rotor points to the point at cylinder 1 at TDC.

shelby27604 said:
Years ago I rebuilt an engine and had a very similar issue, checked and double checked everything. Finally, found the coolant temp. sensor could be snapped in 180 deg. out.

Pulled the plug, flipped it 180 (only 2 poles) and it fired up and ran great.
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I'll take a look at that today when I get home. It's usually something super simple that I have overlooked that causes these issues..:shaking:


rockcity said:
@YJJPWrangler see, simple solution. :lol:
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Very true, but I got the motor for free....
 
Thinking back to your original video of the engine running, I think you have a major timing issue. 180 out, timing chain wrong, distributor off a tooth, something. I've had a 4.3 in my Jeep for close to 20 years and as bad as it has run at times, it has never been that bad.
 
When I tore the motor down, I did not mess with the timing chain. Didn't even pop the cover off. I am still thinking I have it off on the timing. Would the orientation of distributor affect anything? So in a normal application, the distributor is facing forward with the electrical connections in the back. With the small engine bay, I had to turn the distributor to the side so the electrical connections come out the side. Would this cause any issues with the timing? Or does the distributor not care what direction it is facing as long as the rotor points to cylinder 1 at TDC on compression stroke?
 
Annnnnd Im pretty sure I just figured out the issue. Firing order for the 4.3l is 165432, counted clockwise on the distributor. I've got it numbered 123456. :shaking::shaking:

Will correct it later today and see what happens. If this fixes it, I'm a moron and I owe everybody in this thread at least a beer if not more...
 
YJJPWrangler said:
Annnnnd Im pretty sure I just figured out the issue. Firing order for the 4.3l is 165432, counted clockwise on the distributor. I've got it numbered 123456. :shaking::shaking:

Will correct it later today and see what happens. If this fixes it, I'm a moron and I owe everybody in this thread at least a beer if not more...
Click to expand...

Plug wires completely out of order will definitely do that..... :D
 
YJJPWrangler said:
Annnnnd Im pretty sure I just figured out the issue. Firing order for the 4.3l is 165432, counted clockwise on the distributor. I've got it numbered 123456. :shaking::shaking:

Will correct it later today and see what happens. If this fixes it, I'm a moron and I owe everybody in this thread at least a beer if not more...
Click to expand...

That's funny!
 
Well it wasn’t that easy. Counted the wires 3x and am positive that it is timed correctly 612345. On a whim, I pulled the driver side valve cover off to watch the rocker arms move as I rotated the engine. I’m getting some movement out of them but not a lot. My new theory is that when I rebuilt the motor, I didn’t tighten the rocker arm nuts all the way. So the valves aren’t fully opening or closing so no compression. Going to rent a compression tester and see what I find. Any tips on torquing the rocker nuts to spec? Is this new theory plausible.
 
If the rocker arms are not tight, the valves should still close all the way so you should have compression. Also remember that it doesn’t take as much movement as you think to open the valve.
 
Depends what generation 4.3

Most tbi motors have adjustable rockers. You can tighten them till push rod has no vertical play on base circle then half turn. Couple other ways to go about it as well.

You can buy a tester for like $30
 
a_kelley said:
Depends what generation 4.3

Most tbi motors have adjustable rockers. You can tighten them till push rod has no vertical play on base circle then half turn. Couple other ways to go about it as well.

You can buy a tester for like $30
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It’s a 91, pre Vortec. I have adjustable rockers. They way I’ve always done them is to tighten them down so you can barely spin the pushrod then another half turn. There is little to no movement in them at all. So too tight or too loose?
 
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