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S10 surging at ~2100-2500 rpm

steve325is on Mon February 18, 2008 11:18 AM User is offline

Year: 94
Make: Chevy
Model: S-10 PU
Engine Size: 2.2
Refrigerant Type: R 134
Ambient Temp: 63 F
Country of Origin: United States

Any of you GM-heads run into a 2.2 S-10 5mt with a bad buck/surge at 2100-2500 rpm or so? It runs fine under load, runs fine at cruise at any other RPM range and idles fine. This is a fairly low mileage truck (76k). This is particularly annoying because this is the RPM range in 2nd and 3rd gear that you normally operate in in residential areas.

TIA

Steve

CorvairGeek on Mon February 18, 2008 11:49 AM User is offline

Any error codes? Sounds like an EGR valve (assuming no vacuum leaks). Does it have an electronic or a mechanical EGR valve?

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Jerry

NickD on Mon February 18, 2008 12:54 PM User is offline

I like to guess, doubt if it's the EGR valve at 2,500 rpm, thing is suppose to be wide open anyway, or better be. Only need a jumper wire to read all the codes, well a code book will help, have some listed at batauto.com. My guess at that speed range is the MAP sensor or vacuum leaks causing low manifold pressure screwing up the timing. If you have a timing light and a vacuum gauge, that would help, vacuum will be low and the timing mark will be jumping around all over the place. Idle can be okay with this problem, also found bad spark plugs with blowby past the ceramic seals, and only over a small rpm range, but that only happened once. Could be a loose plug that causes that same problem, some guys just put them in finger tight.

steve325is on Mon February 18, 2008 1:46 PM User is offline

Quote
Originally posted by: CorvairGeek
Any error codes? Sounds like an EGR valve (assuming no vacuum leaks). Does it have an electronic or a mechanical EGR valve?


No error codes. It is a negative backpressure type EGR. Sounds like classic EGR symptoms to me too. I am really surprised that is hasn't set a code 32 though. I am not sure what the coolant temp needs to be for the EGR to operate, but the surge happens even before it is at operating temp. I have a golf tee in the cupholder. I may install it for the drive home and see what happens.

I haven't looked at the plugs. It really doesn't feel like a secondary ignition miss to me, but who knows. I have a new set of AC Delcos sitting on the shelf that I was going to install just for maintenance purposes anyway.

Wish this thing was OBD-II. I have an OBD-II scan tool with GM enhanced diagnostics, but it is of course useless on this truck.

-- Steve

CorvairGeek on Mon February 18, 2008 2:18 PM User is offline

The temp EGR starts at can vary greatly. Some earlier versions of the Cavalier engine (2.0L versus your 2.2 rear drive version) used a backpressure EGR valve that opened anytime the throttle opened far enough (no TVS at all). It ran a lot of EGR due the the compression and lack of a knock sensor.

Since you appear to be getting at least some EGR, if only erratic, you probably will not get a code 32 with a mechanical valve.

You will get detonation so uncontrollable (at sea level) you won't be able tell much of anything if the 2.2L is anything like the older cast iron head versions. Fortunately, they seem radically different. Just a thought.....

-------------------------
Jerry

steve325is on Mon February 18, 2008 4:27 PM User is offline

Quote
Originally posted by: CorvairGeek
The temp EGR starts at can vary greatly. Some earlier versions of the Cavalier engine (2.0L versus your 2.2 rear drive version) used a backpressure EGR valve that opened anytime the throttle opened far enough (no TVS at all). It ran a lot of EGR due the the compression and lack of a knock sensor.



Since you appear to be getting at least some EGR, if only erratic, you probably will not get a code 32 with a mechanical valve.



You will get detonation so uncontrollable (at sea level) you won't be able tell much of anything if the 2.2L is anything like the older cast iron head versions. Fortunately, they seem radically different. Just a thought.....


It is a similar EGR valve, but with an ECM controlled control solenoid. No knock sensor on this one either, I don't think. The truck just passed smog a couple of weeks ago, so I agree that it must have "some" EGR. We use a dyno test that measures NOx here in CA, so there is no longer a functional EGR test involved.

This is a much simpler backpressure EGR system than either my old Ranger or Mustang had. I had some issues with the Ranger that kept me going for about a week :-(

I guess I should at least see if the EGR valve is holding vacuum.

Yeah, I am at sea level. The office is about 15' above sea level, my house is about 100' above sea level. Maybe the golf tee wouldn't be such a good idea after all.

-- Steve

CorvairGeek on Mon February 18, 2008 4:42 PM User is offline

At least one of the backpressure type EGR valves will not hold vacuum when applied to a stopped engine. The ECM serves as the TVS for your style, it may be a PWM solenoid, or a simple solenoid. I don't have any service information to say which type it is for sure (not that it matters).

Those Ford backpressure modulation systems are bizarre to me too.

You'll definitely trip a code if you plug the vacuum at the valve. I could only ever "re-meter" the EGR on our 2.0L, it was just too integral to the spark curve/detonation control. I did have to replace the valve on that one too when it was a few years old because the valve was opening too easily and creating a terrific stumble off idle.

-------------------------
Jerry

NickD on Mon February 18, 2008 5:20 PM User is offline

Easiest fix for an ailing back pressure EGR valve is to set the idle speed at 1,800 rpm, little rough on your torque converter if you have AT, but it works. Never did figure out how to test those, but with lots of idle problems, a new one cured that problem.

Favorite EGR valves can be found in my 98 ZX2, 04 Cavalier, and 82 454, none, they use early exhaust valve closing to keep some of the exhaust gases in the cylinder rather than trying to recirculate it. Daughter-in-laws EGR vacuum valve, a bypass type that kept on bypassing the vacuum had burnt exhaust valves. Having an EGR valve is reason for concern, the earlier ones gave no warning. Hers had a PFE sensor, but that wasn't working either, no codes, no warnings. In short, EGR valves are a PITA. If your valve timing goes off, engine won't run anyway, so no concern with this type of exhaust gas recirculation. Books say they are for NOx reduction, true, but who cares about excess NOx's, the way it reduces NOx is by lowering the combustion temperature from around 3,300*F that can burn holes in pistons and melt valves and seats to a more reasonable 2,600-2,700 temperature range. A characteristic of unleaded fuels, that is why lead was added in the first place. Having a wrecked engine due to a bad EGR and/or sensor can ruin your day.

Our S10 4.3 used an electric, new one cost more than what that truck was worth, and putting in a new one didn't increase it's resale value, see yours used a vacuum for around 60-90 bucks. While pulling the plugs, would do a compression check to know were you stand. Was pleased on my 454, got 150 psi on all eight, that put a smile on my face.

steve325is on Tue February 19, 2008 12:21 PM User is offline

Looks like it's fixed!

I started giving the EGR system a close look last night, following the service manual test procedure. The EGR valve "passed" the test, but I really didn't like the way it felt when it opened. I bought a new one, and it operated much smoother. The surge is 99% gone now, and you can actually drive at 2100 rpm in 2nd gear.

Thanks for the input!

-- Steve

CorvairGeek on Tue February 19, 2008 12:52 PM User is offline

That's cool! Just curious, did you buy an OEM or an aftermarket?

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Jerry

steve325is on Tue February 19, 2008 1:24 PM User is offline

Quote
Originally posted by: CorvairGeek
That's cool! Just curious, did you buy an OEM or an aftermarket?


It was a Niehoff. I would rather had an OEM valve, but I didn't want to pay $110 for it or order it online.

-- Steve

CorvairGeek on Tue February 19, 2008 2:10 PM User is offline

Was that one with a selection of orifices (washers) that you had to select the right one for your application? Just curious....



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Jerry

steve325is on Tue February 19, 2008 2:30 PM User is offline

Quote
Originally posted by: CorvairGeek
Was that one with a selection of orifices (washers) that you had to select the right one for your application? Just curious....

No, it was a direct replacement for the vehicle. They even have different part numbers for "us" and "y'all" (CA and Fed). The only issue I have with it is the plastic vacuum fitting. Nick will be proud that it was Made in the USA too.

-- Steve

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