So I bought this s-10 and it has an issue....maybe someone can throw a little knowledge out there, if they have an idea. The truck is a 1995 and is 4.3 V6, 5 speed and 4WD. Super clean and I'm the 2nd owner. Cruising around town, it drives fine, no check engine light, starts fine etc. However, when you go to enter the freeway, and let's say you're in 2nd gear. Push the accelerator all the way down, and the engine only revs to about 3,500 rpm...Wont go any higher... Shift to 3rd, and same deal, accelerates to 3,500 rpm and just hangs out. The strange part is that is doesn't hit a wall like a traditional rev limiter where the engine starts dropping cylinders or the fuel pressure cuts out to avoid over-revving, it just slowly loses power after about 3,000 rpm. Almost as if the accelerator isn't opening the throttle blades all the way...

I don't know much about the truck other than I'm the 2nd owner and the original guy was military, so the truck has 79,458 original miles and is in great shape (the main reason i bought it was to kick around to and from work which is about a 25 mile round trip).

I know the obvious things that can potentially be checked (fuel pressure, map, tps)...but before I start throwing a bunch of money at this thing, I wanted to see if anyone has ever came across this problem before...

My first suspicion is fuel pressure.

Cat(s) getting plugged up?

That thought crossed my mind. However, without doing a pressure test or a IR heat gun temp test (which im sure curiosity will get the best of me and I will do it anyway) I don't think that's the problem. The truck is from out of state, and when you being in a vehicle in Texas from out of state to register it, you have to have a smog test done. It passed emissions about 3 weeks ago. I am only assuming that the cat is good because of the passing grade in Harris county testing facility.

This is a Z engine code, so I will probably start cheap...replace the fuel filter... try and get ahold of a fuel pressure tester at some point in the near future and go from there. Luckily this isn't a pressing issue as its an extra set of wheels...but I figured I would at least see if anyone had this problems/issue first hand....

Wow, that's a new one on me. Is yours the TBI or CPI engine? (Edit: I see you replied while I was typing, and it's TBI. Solid design, but harder to test fuel pressure on, unfortunately. I've been meaning to get a gauge + T-fitting myself. Anyone know a good deal on one?)

I'm inclined to think it's more of an air problem than a fuel one, if you have normal power output at lower RPMs. If you had a bad MAP sensor, vacuum leak, or weak fuel pressure, you'd definitely notice it when flooring it at 2000 RPM, not just at higher RPMs.

First guesses would be partially-blocked exhaust, as has been mentioned, or a really dirty air filter.

If it's not that, then maybe an ignition issue -- if the timing is way off, and/or the distributor, cap, or rotor are badly worn, you might get crossfiring at higher RPMs, especially if the computer decides to advance the timing more at that point. This is kinda grasping at straws though, and I'd rule out the other things first, including a fuel pressure check, just to be certain.

I assume no stored codes either? '95 should be OBD-I so you should be able to the paper clip thing to read them out.

[This message has been edited by Drewmeister (edited 7/17/2011 7:13p).]

It is OBDI, however with an OBDII 16 pin connector. I actually tried to pull codes using the old pin method by connecting 5 and 6...and no SES light will flash...only stays on. Hate to admit it, but I might take it to Autozone and have them pull codes...

I will probably also take a closer look at the cap and rotor....with only 79,000 miles, you would think they would be in good shape still, or at least good enough to run correctly....

is this while the vehicle is parked and in neutral or the clutch depressed? The latest of the TBI trucks has a primitive traction/anti-jackass control and progressively retards the timing the higher the engine revs if the VSS and clutch pedal position switch input show that nothing is supposed to be moving.

The electronic fuel pumps on those don't have a good track record, especially if the previous owner had a habit of running the tank low.

Robert..this happens both while in gear and driving....WWAYYYYY more prevalent when there is a load on the engine...so at highway speed, its easiest to see.

On a side note..I have been thumbing through numerous websites in the past couple of hours and I have found out that I have a 16pin ALDL connector (which is usually typical of an OBDII system) however, my ECM is located in the engine bay on the passenger fender well. This leads me to believe that I have an OBDII system. Evidently if you have the 12 pin ALDL you have an OBDI system. If you have the 16 pin ALDL but your ECM is IN the cab you have a OBD1.5 system...and if you have the 16pin ALDL and the ECM is in the engine bay...its OBDII.

SO bottom line, is i made a mistake in assuming that I could read codes without a scanner, because I assumed that I had an OBD1.5 system). I will try to pick up a scanner from a friend in the morning and see what, if any, codes are stored.

If not, I'm still leaning towards a fuel delivery issue. According to a friend, I should have 9-13 lbs of fuel pressure on the TBI system...so ill try and get my hands on a fuel pressure tester as well....

if your ecm is on the fender its not TBI

and I don't think any obd2 readers will work. Yours is the same as gm obd stuff just with a different plug. If you really want to see live data buy one of these.

http://www.obd2allinone.com/sc/details.asp?item=aldlobd2u


[This message has been edited by robertf03 (edited 7/17/2011 8:54p).]

ECM on the fender, and definitely TBI. Having owned all GM products for the last 16 years, and unfortunately selling auto parts for close to 10 years, I'm all too familiar with GM products.

I will admit though, that my most of my experience with EFI is limited as I have usually owned vehicles that are older and carb'd... Current set of wheels is a TBI 91 S10 Blazer that I've had for 7 years. So my limited amount of EFI knowledge comes from friends who used to burn their own PROMS for early 90's GM cars (a few guys who had heads/cammed IROC Camaros who took their cars pretty serious). Factory PROMS dont do well with .550 lift cams and heads that flow 220 cfm on the intake side. They actually built thier own ALDL cables to read/burn PROMS in late 90's. Come to think of it, those guys spent a LOT of time and effort with TPI...thank God LSx motors came out...

But what is a little disturbing about the whole thing. Is that VIN says code Z, stickers on radiator shroud say OBDI compliant, and ALDL port is 16 pin OBDII and ECM on fender in engine bay....doesn't give me much faith in repairing this thing without throwing a lot of time (and potentially money) away....because it seems that lots of different styles/formats where used from 94,95,96 on a LOT of GM cars and trucks..... There doesn't seem to be a limited amount of options here....soo many combinations have people looking in the wrong places to fix their problems...

Maybe I should just stay off the freeway....

http://www.youtube.com/watch?v=bbBnrCh3IKU

Problem solved

TBI trucks don't make much power above 3500 RPM anyways so you're not missing out on much

odd, I've never encountered an engine bay mounted tbi pcm, but it sounds like you've got one.

Everything I have shows it should use the same datastream as a 94-95 truck v8.

quote:

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odd, I've never encountered an engine bay mounted tbi pcm

---

Agreed, mine is behind the glovebox.

I figured the S10 being a smaller truck maybe there wasn't enough room to put it behind the dash?

See, that's just the thing I'm worried about....weird configurations with this thing.... nothing seems to be "normal"...

I DO like the LSx idea.....maybe at a later date...for now, ill have to mess with the headache I have...

ill keep you posted on fuel pressure and a potential scan....and I appreciate the feedback...

V8 swap into a 4wd S10 is a ***** and a half

My S-10 has the ECM behind the dash/under the glove box too, so there's no lack of room. He just has one of the "OBD 1.5" vehicles where they were halfway through the changeover.

Crazy thought -- your fan clutch isn't seized, is it? I imagine that would be quite a drag (pun intended) at high RPMs.

My money's on the fuel pump.

Quick update, I haven't had a lot of free time on my hands the last few days.... But I did take a heat gun reading of the cat this evening..

Got in, drove down the road a few miles, watched the temp gauge, made sure the thermostat opened and pulled into an empty parking lot.
Took these readings at idle

Front of the cat-290 to 320
Rear of cat - 450-500

I sat under there for a couple of minutes and shot the scanner from the y-pipe to the muffler. I know that cat is designed to operate at a high temp, but damn, that's hot. The immediate reading on the rear of the cat when I pulled over was above 600. The IR gun I have only goes to 600....so it was giving me a ERROR reading. After 45 seconds or so, it came down to readable (550-570) then after a couple of minutes settled in the mid 400's..... The front of the cat reading never really shifted....stayed around 300.

Bad cat? Anyone done this with a newer vehicle? after I got back to the house, I did the same exact test with my 91 s10 with a 4.3 TBI, and had 350 in front of the cat and 320 at the rear of the cat. Keep in mind that the 1991 s10 has 280,000 miles on it....

I want to know if there is a "standard" temp that cats should be around.....

Ill scan it at some point and throw that info out there as well.....

cut dat bish out

increase in temp means your cat is doing something, sounds fuel related.

Rebuild the throttle body, it'll have a new pressure regulator diaphragm included in the kit.

Also pull the air filter and observe the spray pattern to make sure it isn't dribbling out one side.


[This message has been edited by robertf03 (edited 7/21/2011 11:06a).]

Ok...another quick update....

Like I said, very little free time because I coach/teach and coaching responsibilities have already started back up....

In any case. I couldn't help it. No codes were pulled from the ole Autozone scanner. So I drilled a small hole in front of and behind the cat.

Pressure at Idle

In Front of cat - 2 PSI
Behind cat - Gauge wont move (aka 0 psi)


3300 rpm in driveway (no load obviously)

In front of cat - 6 psi
Behind cat - gauge wont move (aka no pressure, and on a side note, you can BARELY feel any air even coming out of the hole behind the cat)

Even the whistling sound from the hole in front of the cat at 3300 rpm with no load is pretty impressive. You can feel the exhaust being blown downward like a hose from a compressor.... So, I'm going to mess with the cat first. there is a convenient splice and muffler clamp right there....too hot to mess with it right now.... but I will pull it down soon enough and take a look.

My worry now, becomes, what took a dump to cause this cat to go bad at 79,000 miles.... Remember, it JUST passed Harris county emissions testing.....

I did pull the plugs and looked at all 6. Very clean, no signs of a rich condition. No oil present...all the electrodes look good. The terminals in the cap and on the rotor looked like they could use replacing, so I took care of that. The wires looked relatively new.

We shall see after it cools what that cat looks like....

I'll keep you posted...

Finally had a little free time this morning. Ive pretty much decided that the issue is with the cat seeing that the temps were so high on the backside, in excess of 600 degrees F. So, much to my surprise, the three rusty bolts that hold it in place backed out without incident. I looked through the cat once I pulled it off from the engine side, and it was very clean, completely intact honeycomb....(im thinking damn..not the issue)...flipped it around, and immediately felt 100% about the whole thing.

The back half of the honeycomb had broken loose inside. It had managed to rattle around and beat it self into the shape of about the size of a baseball. All nice and curved and everything. The shape fit the inside of the cat where it necks back down to the exhaust tubing almost perfectly. It was so perfect, it looked like someone had taken an shaved it down so it WOULD fit. It was definitely plugging up the entire exhaust. No sign of engine issues, just a broken cat.

So bottom line, instead of taking the time to fix it correctly by installing a new cat, I just took a rod and hammer and whacked out the entire honeycomb (i know illegal)....reinstalled the cat...

And its a whole new truck. Pulls nice and smooth all the way to red line. Get out on the freeway, and it accelerates very nicely..(exactly the way a 4.3 V6 should)

So everything seems to be working normally.... Ill replace that cat in due time...found the OE replacement on craigslist for 60 bucks...so maybe sooner than later.....

The End.

That's what I told you two weeks ago.


jk. Glad you got it fixed.

I was waiting on that............

Seriously, I am glad you got it fixed...and for free.

u need 2 cut off teh mufler nd get lik fity mo poniez

You spell badly.