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2001 Chevrolet S-10, 4.3L V6, RWD, Positrac, 3-Door Ext. Cab
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7 Posts
Discussion Starter · #1 ·
General Description and Symptoms
This all started when the EGR valve wiring got messed up (by a rodent? Found a mouse nest in the air box), disconnecting the position sensor, and would fully open and close rapidly, resulting in extremely jerky acceleration. I've since installed a blocker plate and left the valve in place and plugged in. No ECM tuneup since, as of yet. The truck now throws a P0401 code for "EGR insufficient flow." It doesn't seem like that is the source of the problem though. I can get the truck moving as fast as I want it to, but acceleration is very poor, and impossible up hill over 55mph or so. It doesn't seem to be in any sort of limp mode, as the transmission will still use all its gears at normal RPMs while cruising on the highway. Is there another sort of safe mode I should be aware of that might be triggered by my EGR blocker plate? This issue has gone on for a couple weeks now, and I want to get this fixed as soon as possible. Needless to say, I really do not want to damage my engine.

Other Notable Symptoms
My ECT stays at about 198F, which is about 10-12F cooler than usual.
Voltage gauge is just barely lower than 14V, but enough to seem out of place.
Oil pressure moves more than usual. It used to be steady at about 60PSI while moving and about 40PSI while stopped. But it's now between 20PSI and 55PSI. Oil level is fine, but due for a change.
When approaching 3000 RPM trying to go up hill, I can hear a rattling that sounds like it's coming from in front of me, and slightly downwards to the right. Maybe a plugged cat close to the engine?

Tests and their Results
At idle, fuel trims are normal; about the same for revving in park. Under load, such as going up hill, fuel trims are in the +25-30% range, summing ST and LT together for a total. LTs make up the bulk of that; about 20-25, with STs making adjustments of -5-10% once the LTs level out while climbing a hill.
All three O2 sensors read normal under all conditions I was able to test; B1S1 and B2S1 fluctuate (50~900mV) as they should, and B1S2 remains relatively steady (avg. ~600mV) as it should.
Testing the cats with an IR thermometer yielded normal results; ~230F inlet and ~330F outlet for the first, little one; and ~430F inlet and ~500F outlet for the second, bigger one.
Misfires only when under load, but idling relatively rough. It's always idled a bit rough, but currently is noticeably rougher, though only a little.

Theories, Suspicions, and Plans
With these test results, I believe it's safe to rule out a vacuum leak. I still suspect the cats, even though they seemed to check out by two different tests. The aforementioned rattling seems to support this theory.

I've yet to get my hands on a fuel pressure gauge, but I strongly suspect a problem in the fuel delivery system (pump, filter, or regulator). I also suspect a timing problem, but I don't even know how to go about testing it.


If you need any more info, just ask. I'm happy to provide it if I can get a hold of it.
 

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Been there Done it
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12,798 Posts
Do the fuel pressure test and let us know what pressure you get and if it holds after the is key off. Should be near 60 psi KOEO and not drop any for a few minutes. It might drop 5 psi initially, but it should then hold that.
 

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2,115 Posts
Have your catalytic converter tested at a muffler shop.
Take a temp gun under your truck check Temps before and after cat, that will tell you quickly
 

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2001 Chevrolet S-10, 4.3L V6, RWD, Positrac, 3-Door Ext. Cab
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7 Posts
Discussion Starter · #4 ·
Do the fuel pressure test and let us know what pressure you get and if it holds after the is key off. Should be near 60 psi KOEO and not drop any for a few minutes. It might drop 5 psi initially, but it should then hold that.
What is the specified range in PSI for my engine, 2001 4.3L V6? I haven't been able to find it with a bit of digging, and I'm on the fence about buying a service manual. I will definitely report back on the readings. I'm going to try to do it today. I'm most suspecting the fuel filter or pressure regulator.
 

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B4U Task Force Admin
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You don't need to look too far. At the top of this section are stickies. The one by Burned details all you need to know about testing fuel pressure.
 

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2001 Chevrolet S-10, 4.3L V6, RWD, Positrac, 3-Door Ext. Cab
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7 Posts
Discussion Starter · #6 ·
Have your catalytic converter tested at a muffler shop.
Take a temp gun under your truck check Temps before and after cat, that will tell you quickly
Taking it to a shop would probably find the problem faster than I am, but I'd like to avoid diagnostic fees; even if I do end up having to have a mechanic do the fix.
I tested the cats already with an IR thermometer ("laser" thermometer/temp gun). It looks like I have two of them, and they both are normal, with their inlet sides being around 100 degrees cooler than their outlet sides. That also is corroborated by the post-cat O2 sensor, which gives a steady reading rather than fluctuating along with the pre-cat sensors.
 

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2001 Chevrolet S-10, 4.3L V6, RWD, Positrac, 3-Door Ext. Cab
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7 Posts
Discussion Starter · #7 ·
You don't need to look too far. At the top of this section are stickies. The one by Burned details all you need to know about testing fuel pressure.
Ah, gotcha. Thanks, I was at a loss trying to diagnose my problem, so I created this account just yesterday to see if some other S-10 guys could help me out, as I could not find my issue described by anybody else anywhere. So I guess you could say I'm new to the forum, with a whopping 20 hour-old account. lol I'll check out those stickied posts.
 

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2001 Chevrolet S-10, 4.3L V6, RWD, Positrac, 3-Door Ext. Cab
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7 Posts
Discussion Starter · #8 ·
Fuel Pressure Test Port Results
Out of spec. I didn't quite catch where it primed, but it looked like the 66 PSI it should be, and held at about 62 PSI for a short time, but leaked down to 48 PSI after 10 minutes. I haven't tested pressure at the pump yet, but I bought a filter since I'm not sure it has ever been changed anyway and is probably due, and will test pump pressure when I change the filter. That update may come tonight.
 

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2001 Chevrolet S-10, 4.3L V6, RWD, Positrac, 3-Door Ext. Cab
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Discussion Starter · #9 ·
Update, For Those Interested
I had a well-regarded mechanic in my area take a look at it. He didn't charge me anything and looked at it with his scanner which probably costs ten times what mine did. He told me that there is carbon buildup in the engine which caused my first problem (the EGR valve rapidly opening and closing), and I need to change my distributor cap to fix my lack of power. I know the caps on these engines aren't very good, but the one I have on it isn't very old—not even a year—so I was surprised it needs changed already. That is currently underway. He also told me to unhook one of my vacuum lines while the truck is running (I haven't yet checked what this one is for) and slowly trickle Seafoam into it until the bottle is empty, and that should fix the carbon buildup problem which was causing my EGR valve to go nuts (the buildup isn't in the EGR valve, but elsewhere in the loop).
I also learned that the rattling noise was actually coming from right in front of me, and is actually detonation. I'm babying the thing until the problem is all fixed; I hope no damage was done to the engine before I found out what detonation sounds like. It's possible that the EGR problem and my deletion-without-tuneup of it really did cause problems, in combination with a failing distributor cap. I'll let you guys know after I do what I was told would fix the problem.
 

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2001 Chevrolet S-10, 4.3L V6, RWD, Positrac, 3-Door Ext. Cab
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Discussion Starter · #10 ·
Problem Solved
The same mechanic I took it to before took another look at it, and concluded it was the fuel injectors. So I ordered a whole new set with the updated, poppet-less injectors. Problem solved. As it turned out, the liquid gas leaking inside the plenum loosened up the carbon inside, and apparently washed it all into the EGR tube, clogging it up and causing the symptoms related to it (never a wiring problem). The cats were also toast after all this, which the mechanic deleted for me. He cleaned up all the carbon causing issues, changed my injectors, deleted my cats, and let me know about a couple smaller problems I need to take care of. All for a great price.

I hope this helps somebody who has the same issue as I did. I never would have guessed that's what it was. There's no substitute for the experience and expertise of a skilled mechanic.
 
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