98 Z71 k1500 no power or acceleration in drive

Eas6341 · April 7, 2011

Hey I got a 98 454 n it looks like I got that same problem my truck loses power n it runs too rich I floor that gass and it takes time to respond and I do get that metal sound n e help please had my project truck parked like 2 years cuz I don't know what to do..

tazntown9127 · June 20, 2013

I too have a 95 Z71 with the 5.7.i have done everything everyone else has with the acception i have not cat.some one told be that it could be something in the transmission.Is this possible?

1997SierraSLT · June 20, 2013

Welcome to ownership of 1st generation GM Vortec engine. I've owned my 97' GMC Sierra K1500 (5.7L) with 151,000 on the odometer since 1999 when purchased with 17,000 miles on it. If I weren't a mechanic, I wouldn't have been able to afford to own this truck. Constant fuel injection problems, leaking coolant (3rd radiator and 4th intake manifold gasket set), and erratic variable speed steering issues from day one (violent steering wheel jerk at 40mph).

From day one of ownership, I'd get the dreaded P0300 (random misfire) code which would occur any time the engine was put under the slightest amount of load. The engine would fall flat on it's face and shutter/rumble like crazy. I invested in a pocket scanner for sole intent of resetting ECM because I got so tired of looking at that dummy light illuminated on the dash. For the first few years of ownership, I'd take it to GM to have them perform a flush of fuel injection system to loosen deposits that form on the poppet valves. It didn't help any. I'd drive away, romp on the throttle and check engine light was back on again within minutes. Very very poor poppet valve fuel injection design.

About 5 years ago I swapped out the CSFI system with the MFI system (AC/Delco). This helped quite a bit but did not solve the problem. I would still get P0300 codes. However, I immediately noticed the truck had much more low end power as I could break traction much easier. About a year ago, the truck would lose complete power above 70 mph with P0300 code being set. I decided to replace the fuel pump and it helped tremendously. All I can assume is the pump was simply worn out as it would develop enough fuel system pressure (55 psi), but flow rate was reduced. I believe the fuel injectors were simply starved of fuel under high RPM or load.

I will get a P0300 code every once in a while now but I believe its because I do mostly city driving and engine does not get a chance to run at highway speeds for any length of time to help clean out carbon deposits, etc.

Knock on wood, but I've never had to break into engine, transmission or front/rear differentials. The drive train has been quite solid.

I do agree with others who have posted that the catalytic converters could possibly be clogged up. I had an 87' El Camino years ago that I could barely get up to 50 MPH. I changed out the cat and it ran like a new engine. Unfortunately these trucks have two of them and I'm sure they are not cheap.

I suspect those that run an aftermarket K&N air filter element could find themselves with a contaminated mass airflow sensor which could send false readings to the ECM.

Dirtautoguy · July 7, 2013

I kept getting that p0300 code for a long time too in my 5.7 vortec. T

After I had done a full tune up I still got it once in a while so I went a step further and replaced the distributor shaft and I haven't gotten the code since took about 2 1/2 years to find it (I wasn't real serious about finding it for a long time)

1997SierraSLT · July 7, 2013

Replacement of distributor shaft is a first I've heard of on this many topics of discussion pertaining to the P0300 random misfire code. Did you do a side by side comparisons to note any differences in the shaft? If so, please share as the P0300 code is one of the most popular topics of discussion on these first generation Vortec engines.

Dirtautoguy · July 11, 2013

The main reason I replaced the shaft is because someone stripped out the screw hole on the dist cap and had just put a bigger screw in it which worked fine but finally broke the plastic screw hole so the cap would quite fit right. (I had the returning code befor it broke) i looked at them pretty close and I did notice the old one had just barely a slight amount of slop and free play in the shaft but like a minuscule amount. It also had went through 3 or 4 dist caps In 20,000 miles I got the new one from nappa it has a metal body and brass posts in the cap instead of alluminum. I had to use the old mounting bracket because for whatever reason the new one didn't allow the shaft to be turned for timing But that wasn't a big deal. Over all I think the new one is sturdier and better built and I haven't had the code come back and haven't went through any more caps. I gained some mpg too.

Dirtautoguy · July 11, 2013

The slop I noticed was when the platform the rotor goes on comes up (I think for timing advance?) sorry I don't know alot about how it's built. I don't recall if the new one had this slop or not. I still have the old shaft maybe ill re examine it and see If i can remember or come up with more.

94C1500 · August 28, 2019

I am having all these same issues but I have no cat. New exhaust headers all the way back. Had a header gasket leak I thought was the problem, but now fix would that have torched my maf? Or my spark plugs? Making it act this way? My fuel gauge also bounces around did that for months before I even redid my exhaust and had these problems.

riverbanks · August 28, 2019

Two different injection systems talked about on this thread,yours is tbi,some on here are vortec,96 and newer, explain a little better what problems you are having