Film-Tech Forum ARCHIVE: Can you help me fix my truck?

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Posted by Richard Greco (Member # 2032) on 04-05-2004, 06:02 PM:

Here is what I have

91 S-10 Blazer 2wd
4.3 TBI
Automatic Tranny

When I am in ANY drive gear, when I get around 30-40 mph and I am light on the accelerator (Keeping that speed) The truck starts to buck. If I press the gas a little harder, It goes away.

I have changed plugs, wires, cap, rotor, O2 sensor and it still does it.

Could it be the catalytic convertor? If so, how do I stop this bucking?

I also have changed the fuel filter recently.

Posted by Mark Gulbrandsen (Member # 72) on 04-05-2004, 06:57 PM:

Does the "Trade It In On A Ford" light come on when this happens? If you bring it by my house I'll be happy to take a look.

Mark

Posted by Floyd Justin Newton (Member # 1316) on 04-05-2004, 07:04 PM:

Mark--

Your're such a SWELL guy!!

fjn [Big Grin]

Posted by Chris Hipp (Member # 1788) on 04-05-2004, 07:58 PM:

Describe bucking a little more in deatail.

If your engine is trying to die then your exhaust will not be at fault, unless you are plugged up completely.

My first thought would be that you arent getting enough gas or perhaps an improperly timed ignition. Did this occur before or after you changed out the distributor parts?

I had a 2.8l s10 a few years ago and when the timing was off it would run for s econd after I killed the switch, is that happening?

I'm sure Erik ackers will be along shortly to give you the exact problem and detailed instructions on how to fix it.

Posted by Bruce McGee (Member # 131) on 04-05-2004, 07:58 PM:

Have you checked the computer? Autozone will test it for free...

Sounds like the TPS (throttle position sensor) could be bad. I have a 1986 Pontiac that had the same problems. That was it!!

Right now, with the insane gas prices, I'm oh so glad to have this Pontiac with its 2.5 cid engine, and 30 mpg habit. So what if it is rusted out...

Posted by Mark Gulbrandsen (Member # 72) on 04-05-2004, 08:00 PM:

Common, he knows what I mean by that.... [Wink]

The check engine light can definately signify a problem in the polution or fuel system..... possibly but not necessarily the catalytic. In order of frequent failueres would first be the oxygen sensor. Oxygen sensors fail far more often than catalytics do. A good place to start is to check the engines self diagnostic indicator to see if its going to tell you anything. Bruce's hint of the position sensor is alsoa good starting point. These systems are always a process of elimination to get to the cause.

My KIA had a problem something like this and it turned out to be a bad intake manifold gasket. Replacing it solved the problem and although it has 120K on its odometer it has extremely low emmissions.

Mark

Posted by Richard Greco (Member # 2032) on 04-05-2004, 08:27 PM:

The bucking is a minor buck at 35-40mph, The engine doesn't want to die but the bucking is noticable.It doesn't want to stay on after I shut down the ignition. I replaced the engine in it and I changed the dist parts as soon as I got the truck back from the shop. I never drove it before I got the engine changed.

I'm not throwing any computer codes. I'm just a little stumped.

Posted by Bobby Henderson (Member # 840) on 04-05-2004, 09:38 PM:

I'm no expert mechanic, but have had a good amount of experience driving GM vehicles. Some of your problems remind me a little of issues I had with my 1992 Camaro. I replaced the alternator three times through its life (with the third replacing a lifetime warranteed unit). The ignition also went out around that last alternator change. Of course, if the problem is with the alternator, it will bleed the charge from your battery and shut down the whole works while you're driving.

Posted by Jason Burroughs (Member # 68) on 04-05-2004, 10:51 PM:

Almost sounds like a case similar to vapor lock. May want to check the fuel filter. If the filter is clogged it could cause the engine to run too lean, resulting in the bucking. Under heavier acceleration the problem is not as noticable due to increased fuel flow.

A clogged fuel filter will also starve your engine of power, and decrease fuel milage.

Start with the simple things first.

Posted by Dino Panagiotopoulos (Member # 1579) on 04-06-2004, 12:13 AM:

My guess is that it could be your mass air sensor. Most likely its allowing too much air in. The car could probably be running too rich so I would have it taken in and check the air/fuel mix ratio. If they run it through a diagnostic machine it should be able to figure out the problem for you.

Another good idea is what Bruce brought up, which is to check the TPS sensor. I had a similar problem on my car and this sensor was one of the problems. These are both pretty cheap to change out compared to some other suggestions. I would give them both a starting point. Good luck

Posted by Jason Thode (Member # 1854) on 04-06-2004, 12:34 AM:

You could always trade it in and buy a hummer and make better Friends with Joe. [thumbsup]

Posted by Chris Hipp (Member # 1788) on 04-06-2004, 12:49 AM:

Dino has a good point, after I put a K&N filter on my 78' honda it would get too much air and not want to die.

Posted by Erick Akers (Member # 875) on 04-06-2004, 03:20 AM:

Hmmmmm,
I must have dazed off; I thought I heard someone talking about me, the name sounded similar but not quite the same. [Confused]

Richard have you ever replaced the cat, because it's time! [Big Grin]

Relax, I need some information first.
Just the basic facts, can you show me where it hurts?

1. Does your check engine light work?

Sometimes they do burn out, but if you checked your codes and you just have the standard code 12 comming up it has not set any error codes.

2. how many miles logged on the cat?

The factory cats are good for about75 to 85,000 miles before they start to take a dump.

The hint that it's going bad, is the exact symptom you are experiencing, that is, a chuggle or shudder in the engine at about 30 to 40 MPH.

In the last two years I have replaced one on our 1987
Chevy Astro (87,245 on the odometer) and one on my late uncle's
91 Safari Van ( 91,366 on the o.d.)

Both of them have the 4.3L engine and both have gained their origional fuel economy back! With these engines, you should see usually about 18 MPG Hwy driving in the S-10,S-15 Astro, and Safari vans.

If you are seeing fuel consumption in the range of 12 to 15 MPG then this too is also a hint of it being the Cat.

All of the sensors that have been mentioned, are in line before the cat in the emmitions chain, and thus have not set any error codes yet, but let this go any longer and they will begin to make their selves known!!!

The Astro's 02 sensor did, the one in the Safari didn't, but did shortly after the replacement of the cat.
So it would be a good idea to replace it at the same time.

BTW: I have the actual GM shop manuals and suplements, so this is more than a guess or shot in the dark.

I do all of the mechanics on everything we own, and I have been impressed with how well built and long lived the 4.3L engines have been so far.

As long as you can prevent oil leaks by replacing all outer gaskets when necessary(valve cover, timing chain,and oil pan gaskets) and change the oil at reasonably regular intervals, I don't see why you shouldn't see 300,000 Miles!

The only thing that have been replaced on both engines aside from gaskets were the oil pumps. They also start to go out about at about 80 to 90,000 miles.

By keeping an occasional eye on the oil pressure gage, and knowing your normal oil pressure range. when the oil pressure starts showing signs of a lower range during normal operating temperature, and you have checked your oil level as full, it's time for a new oil pump.

When I replaced them, I chose the high volume pumps to assure good lubrication for longer life.

Oh, and also one more thing, sometimes the fuel pump could be slowly going out, but not throwing the code, but I really dont believe that this is the case.

If you have any questions,

Feel free to ask!!! [thumbsup]

(for Chris)

Get the name right next time or Ill find you and you and
Kick your Arse!!! [Wink]

Erick

Posted by Bruce McGee (Member # 131) on 04-06-2004, 06:47 AM:

Hey...

This is not the ass-kicking thread! [Smile]

When I had to replace the fuel pump on this Pontiac, the symptom was: Ran fine at idle, and low drive speeds... Lost power when pulling hills, especially with 1/4 tank of gas or less. After checking everything else, I gave up and replaced the pump in the tank. It was a 3 hour job. I knew I was on to something when I tried the pump after the replacement. What a flow difference! Instant power increase!

The MAP sensor was one that I didn't think about. This car's MAP sensor was replaced after I couldn't find anything else to blame. I didn't buy a new one. I had a used one off of a Fiero to try. Problem solved.

I've done all of my own car repairs since 1970.

BTW: The cat on this car is original. 262,000 miles and counting. This car passes our state emission tests. It wouldn't pass before the repairs.

As for a stopped-up cat, my 1985 Olds Toronado would overheat somewhat while driving up long hills. Eventually, it began losing power. Replacement of the cat cured it. The difference in this and the Pontiac is that the Olds has not had alot of high-speed driving. I figured that the cat stopped up over time due to moisture and carbon build-up.

One good thing is: All my cars have stinking exhausts again! Rotton eggs! Makes me feel like they are new again... NOT!

We won't discuss my FORD truck with 310,000 miles on it!

Posted by Sam Hunter (Member # 1119) on 04-06-2004, 07:24 AM:

My 91 S10 Blazer is getting close to 285000 and is going strong.
The most common problem that manifest itself with the symptoms you mention is a clogged fuel system. It would not hurt a thing to replace your fuel filter and see what happens.
Vacuum leaks as someone stated usually affect idle performance and not open throttle conditions.
In any case, good luck.

Posted by Chris Hipp (Member # 1788) on 04-06-2004, 10:17 AM:

Oh, whatever Erick, how self absorbed are you? There is more than one Erick/Erik Akers/Ackers in the world. I guess you assume that becasu the name is similar to your's that I must have been talking about you. How arrogant. Nah, I'm just joking, I was referring to you, but didn't rememebr how to spell your name. [Razz]

Posted by Erick Akers (Member # 875) on 04-06-2004, 05:13 PM:

Chris,

I know,
Same here! [Big Grin]

Richard,
Let us know what you find out.

Posted by Richard Greco (Member # 2032) on 04-06-2004, 11:15 PM:

Erick,

I used a Snap-On diagnostic scanner to test it and I didn't throw any codes. I plan to have the scanner hooked up and do a road test later this week. The tps was in a normal range and didn't hesitate when the scanner was hooked up. That's all I know for now

Posted by Tim Reed (Member # 137) on 04-09-2004, 11:12 AM:

I had an S-10 that had the same problem, but it didn't do it all the time. Maybe just when it was a certain temperature outside, who knows? Never did find out for sure. I used to get aggravated with it sometimes and just floor the SOB to blow it out. Seemed to help. My disposition, anyway.

Posted by Juan Urias (Member # 1990) on 04-09-2004, 11:46 AM:

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