# '98 Z71 power drop, terrible gas consumption



## aubbie (Apr 25, 2011)

I have a 1998 Silverado Z71 with a Vortec 5.7, or 350. I bought it last year and didn't plow much with it...It was mid winter when I bought it. I had it all done over, painted, etc. It works good but I have noticed for a 350 it doesn't have a lot of power, and the $30 worth of gas will get me down the road not too far, and I can see a big difference even since I've had it. I'm putting my plow on it this weekend but would like to get this problem solved before that. I mean it seeks to work OK other than the low power and terrible gas mileage. A friend suggested it might be the catol. converters, and maby they're plugged. I put my scanner on it..it reads emmissions which lends me to think that as well. Has anyone else had that problem? I don't know when it's had a tune up last, but it's not skipping or hitching, it works like it should except for these problems. Please help, and thank You


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## dieselss (Jan 3, 2008)

One thing you can do is feel the exhaust pipe for flow. You could also use a I.r. temp scanner before the cat and after. Last you could try a back psi tester that goes into the o2 ports


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## Snowzilla (Oct 24, 2009)

How many miles on engine? You could also do a compression test on the cylinders to determine if is within specs. A worn engine would have less power and not as efficient.


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## aubbie (Apr 25, 2011)

Thanks dieselss, I'll get my mechanic to try those things...snowzilla pretty sure the engine is not worn out. I have had many 350's, plus this truck had more power last year when I bought it. It purrs like a kitten, doesn't smoke, oil looks good. I'm going to try a few things before I start pulling plugs...I DO have a compression tester though. Thanks Guys...Dieselss, I'm going to have to start paying you! Thanks for the help with the lighting also


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## grandview (Oct 9, 2005)

What's 30 bucks bucks up there,about 5-6 gals of gas,so yea,you won't get to ear with that little amount of gas. Also don't drive with the plow on it you don't have too.


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## aubbie (Apr 25, 2011)

Yes $30 is 6us Gallons, and 22 Litres which is the standard we in Canada go by, don't ask me why. We changed to the metric system around 40 years ago but to me 65 MPH is still 65MPH, and not 110KPH which is kilometers per hour. It's funny though, the young people here don't understand miles per hour, they learned the metric system in school. It would be so much easier if both countries went by the same system. I mean we have the longest commen border in the world, and what you do, we soon will or you Guys will come up in the middle of the night and take over; and pretty soon we'd all be speaking American!


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## grandview (Oct 9, 2005)

Eh? Couldn't hear you.


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## aubbie (Apr 25, 2011)

Couldn't hear me? I must have missed somethimg...anyway yes, $30 is 6 gallons of gas. I just meant that I am burning a lot of gas, a lot more than I used to, so I think I'm having some sort of engine trouble. And I don't normally drive the truck with the plow on unless I'm plowing....costs too much to haul all that weight around


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## dieselss (Jan 3, 2008)

Do you short trip the tk as well? Or do you take it out and cruze so to speak? 
Just stop the check in the mail lol


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## aubbie (Apr 25, 2011)

I'll get that check in the mail in the morning, no problem! I have to ask you something.....what is the tk? Can't figure that one out!


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## Snowzilla (Oct 24, 2009)

Well the 5.7 is a usually potent long lasting engine. But head gasket / intake gaskets have been known to fail.


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## aubbie (Apr 25, 2011)

Yeah who knows...I'll find out when I get it to my new mechanic early next week. By the way the engine has 150,000 miles on it


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## Mister Plow (Jan 21, 2009)

I thought you Canucks wrote cheques.


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## aubbie (Apr 25, 2011)

Mister Plow, I see you've been chequeing out our national news....something to do with a $90,000 Cheque perhaps?


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## dieselss (Jan 3, 2008)

Tk.....truck 
Pwr.....power
Gnd......ground


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## woodchuck2 (Dec 4, 2010)

I am going to say start with replacing the coolant temp sensor and i think you may have a problem with the fuel "spider" in the intake which are noted for cracking and leaking fuel. This will cause loss of power, poor running and excessive fuel consumption.


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## aubbie (Apr 25, 2011)

Have to say I've never heard of the fuel spider in the intake....where in the intake is that?


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## road2damascus (Apr 26, 2010)

spider fuel injection: http://i657.photobucket.com/albums/uu297/eemann1mmckin/DSC01514.jpg

If you are going to check for puddles of fuel in the intake plenum, buy a new gasket ahead of time. The gasket it self can be faulty causing a drop in vacuum readings to the computer. Faulty readings leads to poor fuel management by computer.

The spider fuel injection system is a main cause of many fuel issues. Rock auto has remanufactured ones and you get money back when you send your old one back.

Other things
Clean all sensors with mass air flow sensor cleaner from your local parts store.
Clean egr valve 
Check vacuum lines. Diagram is under hood.
How do your brakes feel? A problem with the vacuum system would cause the brake booster to not work as well. This would make it feel like you no longer have power brakes.

If exhaust smells like rotten eggs then your cat is working over time meaning the engine is dumping way too much fuel in there. Doesn't necessarily mean cat failure but could be the case.

That should keep you busy.


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## aubbie (Apr 25, 2011)

Yeah and now that you mention it, I have been getting a bad smell....smells like a combination of gas and rotton eggs but I just brushed it off. I;m not a mechanic but I'll get someone to do there things....doesn't sound too expensive is it?
Thanks a lot


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## carkey351 (Oct 18, 2010)

*fuel pressure regulator*

Given the year of truck, its not a super high pressure system, but they all have a fuel pressure regulator. Once the diaphragm goes in it, it will start hoovering (sucking in through vacuum line) fuel. if it gets bad enough it will fill the crankcase with gas. (bad, bad washes oil off bearings, etc.). All you need to do is pull the vacuum line off of it, start engine. usually they will spray gas out of the regulator if bad. I've replaced a couple of them, and each time that was what caused the high fuel consumption.

2. the other cause could be a throttle position sensor that is sticky/bad. I don't know if that model is new enough to have one of those, but on my 97 neon it caused it to go from 30mpg to 10mpg, a huge drop. You can usually OHM/voltmeter them out to determine if faulty.

everyone else mentioned stuff that doesn't seem like it matches the symptoms quite right.


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## aubbie (Apr 25, 2011)

Thanks Carkey, I will check both those things Monday. I might have to find out how to perform these functions on utube.....would you suggest that? I can change starters, alts, stuff like that but that's as far as it goes. I rely on you Guys a lot! I'm going away overnight....taking the 2.8 30 valve Passat 4motion.....I should have a plow on front of that.....great in snow!


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