1999 sierra jerking at highway speeds

[Wookiebeast]

I have been noticing that my truck has started to jerk a little with loss of power when driving. It is most noticeable when going up hills or with the cruise on. I recently had to replace the fuel pump and changed the fuel filter as well. I have checked for vacuum leaks on the throttle body and intake with none apparent. I have changed plugs and wires too. There is no loss of antifreeze and none in my oil so my head gasket should be fine. My gas mileage has gone down 2 mpg with no change in brand of fuel (chevron) or driving habits. I did check the codes and the only one that came up was P0107 or low input on the map sensor. Could this sensor cause this kind of problem? Has anyone else experienced this? I am at a loss because I keep my outfits very well maintained and rarely have problems.

Wookiebeast

[tinstar]

My 1998 Z71 5.7 is doing the same thing.
It seems to be getting worse and I have also changed all the things you mentioned except the ingition coil.

The only thing I can think of is maybe clogged converters.
I have over 250,000 and do a lot of highway driving and put lots of gas through it.

The codes I get mention the caytalist system (Bank A and B) are below where it should be.

I am looking to replace them next week.

[tinstar]

I had my Cat Converters replaced yesterday and also put on a Flowmaster Series 70 dual exhaust.

The Stock cats showed a lot of clogging on both the entry and exit sides.

I drove it away and a few miles out had a chance to see if the problem was fixed and it STILL does it.
Yes I have changed the fuel filter and I also bought a new Ing. Coil to see if that might fix it.

I have had the injectors cleaned by the dealership about 3 months ago.

Any ideas!?!?!?

[Wookiebeast]

Well the trouble codes were right about the problem with my truck. It was the MAP sensor that went bad and was causing all the jerking. I replaced it and all is well.

tinstar- Are you taking your truck to a dealership or a local garage to get diagnosed? It might cost a bit more but to go to a dealer. They deal with Chevy’s all day long and might know something about your problem that the local garage won't. It might be cheaper than just replacing parts that your not sure need to be replaced. Did you check your fuel pump because I recently had to get mine replaced at around 100,000 miles. They are known for going around 100k so it might be time for another one.

Sorry but these aren't easily worked on 70's trucks anymore. Too darn many electrical things can go wrong. If I can't clearly diagnose it then I bite the bullet and run it to the dealership.

WB

[tinstar]

I have not taken it to a dealer for a good check.
I did replace the fuel pump about 10 months ago.
What is a MAP sensor anyway?
Where is it and how much did it cost?

I haven't had any codes except for the cat converters.

?????????????????

[Wookiebeast]

A MAP sensor stands for manifold absolute pressure. It is located underneath the black cover that says Vortec on the top of your engine back towards the firewall(99 GMC sierra). It is the sensor that is up high all the way to the back. The MAP helps regulate fuel/air mixture. You should buy a mechanic book for your truck if you need more help.

If you have an Autozone near you they will check your trouble codes for free. You probably won't have any unless your check engine now or soon light is on.

It was like $80 from the dealership or I think $55 special order from checker auto.

[Wookiebeast]

One other thought is the MAF sensor that is connected to your air filter box. This one also regulates fuel/air mixture but is almost twice as expensive as the MAP sensor. If you don't know what your doing with this one get a manual to show you how to test it. Check your codes first before you mess with it.

[tinstar]

I have a Superchips programmer that I use to check codes. I don't have in the performance option (Gas is to high to run premium).
I only have the speed limiter off and adjusted for tire size.

I didn't mention that I did install a K&N Fuel Injection Intake Kit a few months back.

My problem didn't start until about a month ago.

If the MAP is bad, would I get a check light for sure?

I notice the problem now (in addition to described below) on straight and level ground at speed. When I apply some throttle it seems to shutter until you really put the gas to it or back off a little bit.

The power still sucks. When you are stopped and stomp on it, it used to bark the tires really good and now it doesn't.

[sherman69]

Originally Posted by tinstar

I have a Superchips programmer that I use to check codes. I don't have in the performance option (Gas is to high to run premium).
I only have the speed limiter off and adjusted for tire size.

I didn't mention that I did install a K&N Fuel Injection Intake Kit a few months back.

My problem didn't start until about a month ago.

If the MAP is bad, would I get a check light for sure?

I notice the problem now (in addition to described below) on straight and level ground at speed. When I apply some throttle it seems to shutter until you really put the gas to it or back off a little bit.

The power still sucks. When you are stopped and stomp on it, it used to bark the tires really good and now it doesn't.

---------------------------------------------------------------
Hi,
I just read a tech tip that said if an aftermarket air filter such as K&N is over oiled it can cause this type of problem.
You should chec to see if the MAF is oily, or the area around it in the air flow.
Bob B

[Wookiebeast]

Thanks Bob,

That's good to know. I have been considering getting an K&N kit and wondering if you guys like them. Did you notice an increase in gas milage or power? I currently get 18mpg if I keep the tac at or below 2 grand. All stock 5.3 liter engine extended cab Z71.

[tinstar]

I just changed the MAP sensor and the trouble is gone!!!!!

It was oiley and almost clogged.
I got it from O'Rileys.
Borg/Warner part for $45.

The throttle response is MUCH better!!

I did notice with the K & N that the power is better and my mileage went up about 1 1/2 a gallon.
The noise is louder than stock and it sounds like a 4 barrel carb when you floor it.
Still worth the money.

Ebay is the cheapest place to buy the kit. I saved over $60 on mine.
That was even after shipping and the box was factory sealed.

Thank you very much for the tips and suggestions!!!!!!!!!!!!!!!!!!!!!!

[tinstar]

I forgot to add that I never did get a MAP Check Engine light.

Thanks again!!!