Rough idle, bogs and loses brake assist in gear, low rpm.
#1
03-21-2018, 07:49 PM
Rough idle, bogs and loses brake assist in gear, low rpm.
I've got a 93 s10 Blazer 4.3 vortec. A couple months ago I was stopped at a red light with my gas light just coming on and the engine suddenly stuttered and died. After starting it back up, which took a bit, the idle was really rough and if I wasnt revving the engine up the brake assist wasn't working. After getting it home I tested fuel pressure, thinking I burned or damaged the pump, and it didn't seem to be going up to the 58-60. Instead it would go up a random amount like 10, or 25. It would keep pressure wherever it landed over time though, so I went ahead and decided to try the pump instead of the fuel pressure regulator. So far I've replaced the pump, spark plugs, cap and rotor. I am not getting any trouble codes, and I removed the iac and egr to take a look at them but they were pretty clean. I started the engine with the egr still off to make sure I'd even get a code if it were bad and I did get the code. Not entirely sure what to check next. Planned on checking for a timing jump when I track a light down. Any ideas would be appreciated.
Last edited by calebsmith12890; 03-22-2018 at 02:00 PM.
#2
03-21-2018, 08:31 PM
So, what's the fuel pressure after the new pump? Before you threw a pump at it, you should have checked pressure at the fuel pump itself. At the test port will be testing the whole system.
#3
03-22-2018, 01:42 PM
I have not checked yet, was planning on renting the fuel pressure tester again but it started pouring out. As soon as I do I can update. To be honest though I was questioning wether the results of the last test were from a bad tester rather than my actual pressure but I don't kniw. Is there anything else you recommend I check in the meantime?
#4
03-22-2018, 01:57 PM
Last edited by calebsmith12890; 03-22-2018 at 02:08 PM.
#6
03-22-2018, 05:10 PM
That's something I wouldn't know how to do unfortunately, but I'll see if I can figure it out. Is that something that could have gone bad instantly? It does have a low battery from sitting for months, when jumping it starts a lot quicker.
#7
03-22-2018, 06:07 PM
You can watch You Tube videos on doing a compression test. You'll need a compression gauge which you can get as a loaner from auto parts stores if you don't want to buy one. They're not really expensive. The fact it isn't starting quick is what allowed us to hear the cylinder compression. If you disable the engine from starting (pulling a fuel pump relay is one way) and crank the starter for about 10-15 seconds you can hear the compression on the cylinders (or rather the strain or lack thereof on the starter). NOTE: This is only a preliminary test and needs to be verified with a compression test. While the truck is cranking (with fuel disabled) you should hear and even cranking sound. If you hear high "straining" sounds (starter turners slower) combined with some "low straining sounds" (starter turns faster), the low straining sounds could be low compression in one cylinder or more. You do need to do this with a fully charged battery.
If you have low compression, many things could go suddenly...burnt exhaust valve, hole in piston, broken valve spring, etc. But then there is also wear and tear which over time wears out cylinder walls, piston rings, etc without proper maintenance and regular oil changes.
After fuel and air go into a cylinder the valves close and the piston compresses the fuel/air heating the mixture up and making it highly volatile. Spark from your plug ignite this to cause the explosion which ultimately rotates your crank. Fuel and air aren't enough to cause a strong enough explosion by themselves. The mixture must be compressed also. So low compression, if low enough, can cause a "dead" cylinder. Or, let's say you have a valve that is stuck open, as the piston moves up it pushes the mixture out of that opening which again produces a dead cylinder.
When you have good compression, the starter has to draw more amps and works harder. When you have low compression the starter doesn't have to work hard when the that cylinder is on it's compression stroke. That's what your hearing on the starter.
Once again, what I heard is only preliminary, do a compression test to be sure either way.
P.S. A stretched timing chain or a chain that has skipped a tooth can also cause your valves not to seal completely when the pistons are on their compression stroke.
If you have low compression, many things could go suddenly...burnt exhaust valve, hole in piston, broken valve spring, etc. But then there is also wear and tear which over time wears out cylinder walls, piston rings, etc without proper maintenance and regular oil changes.
After fuel and air go into a cylinder the valves close and the piston compresses the fuel/air heating the mixture up and making it highly volatile. Spark from your plug ignite this to cause the explosion which ultimately rotates your crank. Fuel and air aren't enough to cause a strong enough explosion by themselves. The mixture must be compressed also. So low compression, if low enough, can cause a "dead" cylinder. Or, let's say you have a valve that is stuck open, as the piston moves up it pushes the mixture out of that opening which again produces a dead cylinder.
When you have good compression, the starter has to draw more amps and works harder. When you have low compression the starter doesn't have to work hard when the that cylinder is on it's compression stroke. That's what your hearing on the starter.
Once again, what I heard is only preliminary, do a compression test to be sure either way.
P.S. A stretched timing chain or a chain that has skipped a tooth can also cause your valves not to seal completely when the pistons are on their compression stroke.
Last edited by rockp2; 03-22-2018 at 06:23 PM.
#8
03-27-2018, 01:48 PM
You can watch You Tube videos on doing a compression test. You'll need a compression gauge which you can get as a loaner from auto parts stores if you don't want to buy one. They're not really expensive. The fact it isn't starting quick is what allowed us to hear the cylinder compression. If you disable the engine from starting (pulling a fuel pump relay is one way) and crank the starter for about 10-15 seconds you can hear the compression on the cylinders (or rather the strain or lack thereof on the starter). NOTE: This is only a preliminary test and needs to be verified with a compression test. While the truck is cranking (with fuel disabled) you should hear and even cranking sound. If you hear high "straining" sounds (starter turners slower) combined with some "low straining sounds" (starter turns faster), the low straining sounds could be low compression in one cylinder or more. You do need to do this with a fully charged battery.
If you have low compression, many things could go suddenly...burnt exhaust valve, hole in piston, broken valve spring, etc. But then there is also wear and tear which over time wears out cylinder walls, piston rings, etc without proper maintenance and regular oil changes.
After fuel and air go into a cylinder the valves close and the piston compresses the fuel/air heating the mixture up and making it highly volatile. Spark from your plug ignite this to cause the explosion which ultimately rotates your crank. Fuel and air aren't enough to cause a strong enough explosion by themselves. The mixture must be compressed also. So low compression, if low enough, can cause a "dead" cylinder. Or, let's say you have a valve that is stuck open, as the piston moves up it pushes the mixture out of that opening which again produces a dead cylinder.
When you have good compression, the starter has to draw more amps and works harder. When you have low compression the starter doesn't have to work hard when the that cylinder is on it's compression stroke. That's what your hearing on the starter.
Once again, what I heard is only preliminary, do a compression test to be sure either way.
P.S. A stretched timing chain or a chain that has skipped a tooth can also cause your valves not to seal completely when the pistons are on their compression stroke.
If you have low compression, many things could go suddenly...burnt exhaust valve, hole in piston, broken valve spring, etc. But then there is also wear and tear which over time wears out cylinder walls, piston rings, etc without proper maintenance and regular oil changes.
After fuel and air go into a cylinder the valves close and the piston compresses the fuel/air heating the mixture up and making it highly volatile. Spark from your plug ignite this to cause the explosion which ultimately rotates your crank. Fuel and air aren't enough to cause a strong enough explosion by themselves. The mixture must be compressed also. So low compression, if low enough, can cause a "dead" cylinder. Or, let's say you have a valve that is stuck open, as the piston moves up it pushes the mixture out of that opening which again produces a dead cylinder.
When you have good compression, the starter has to draw more amps and works harder. When you have low compression the starter doesn't have to work hard when the that cylinder is on it's compression stroke. That's what your hearing on the starter.
Once again, what I heard is only preliminary, do a compression test to be sure either way.
P.S. A stretched timing chain or a chain that has skipped a tooth can also cause your valves not to seal completely when the pistons are on their compression stroke.
#9
03-27-2018, 01:53 PM
After googling around It seems entirely likely that if the flooding was washing out the oil rings, I caused damage in the cylinders by running the engine anyway. I wonder if that's the case whether or not it's even worth dumping the 300 or so dollars into parts replacement.... is there a chance that the damage isn't so bad that replacing the spider would at least make it run decent?
Last edited by calebsmith12890; 03-27-2018 at 01:56 PM.
#10
03-27-2018, 05:19 PM
I the cylinders on one bank have been washed out from fuel, changing the spider is not going to solve the problem. The damage is already done and the cylinder walls are beyond minor repair. The cheapest possibility (not counting changing the injectors) would be a ring job with oversize rings.
But more than likely you would want to take the block to a machine shop to have it magnafluxed and the cylinders honed. Honestly, if you want to keep the truck I would buy a long-block. You'll have a completely rebuilt engine with a warranty. You'll probably be spending in the neighborhood of $2k (+/- a few hundred). Or you could get a short-block which would be cheaper and basically you just have to move the heads from your old engine to the new one (and a few other things).
But, before condemning the engine you have, I'd want to know what the compression numbers were for each cylinder. I'd also do some of my own testing to insure timing chain didn't slip, etc. The shop stated that the fuel washed out the oil rings, but you'd have to tear the engine down to see if the cylinder walls are good enough just for a ring job. But the minimum you'd want to do is a "crank kit" ( https://www.enginepartsonly.com/1993...EaAumuEALw_wcB ). Link is just an EXAMPLE I grabbed real quick.
Everything depends on how attached you are to the truck, how much you want to spend, if you'll do the work yourself, etc, etc,etc. Personally, I love my '98 ZR2 and I put a long-block in about 40k miles ago.
Again, bottom line, new injectors are alone not going to do anything at all for washed out cylinders. Washed out means the cylinder walls & rings were not being lubricated (basically) because the fuel was washing away the oil and you had metal on metal scrubbing against each other. It is also possible that your main bearings and the other moving components could have been adversely affected if you got a high amount of fuel into the oil.
P.S. There is also the option of a junkyard engine.
But more than likely you would want to take the block to a machine shop to have it magnafluxed and the cylinders honed. Honestly, if you want to keep the truck I would buy a long-block. You'll have a completely rebuilt engine with a warranty. You'll probably be spending in the neighborhood of $2k (+/- a few hundred). Or you could get a short-block which would be cheaper and basically you just have to move the heads from your old engine to the new one (and a few other things).
But, before condemning the engine you have, I'd want to know what the compression numbers were for each cylinder. I'd also do some of my own testing to insure timing chain didn't slip, etc. The shop stated that the fuel washed out the oil rings, but you'd have to tear the engine down to see if the cylinder walls are good enough just for a ring job. But the minimum you'd want to do is a "crank kit" ( https://www.enginepartsonly.com/1993...EaAumuEALw_wcB ). Link is just an EXAMPLE I grabbed real quick.
Everything depends on how attached you are to the truck, how much you want to spend, if you'll do the work yourself, etc, etc,etc. Personally, I love my '98 ZR2 and I put a long-block in about 40k miles ago.
Again, bottom line, new injectors are alone not going to do anything at all for washed out cylinders. Washed out means the cylinder walls & rings were not being lubricated (basically) because the fuel was washing away the oil and you had metal on metal scrubbing against each other. It is also possible that your main bearings and the other moving components could have been adversely affected if you got a high amount of fuel into the oil.
P.S. There is also the option of a junkyard engine.
Last edited by rockp2; 03-27-2018 at 05:29 PM.