dancer52 Posted December 11, 2004 Report Share Posted December 11, 2004 I have a 98 chevy 3/4 ton truck, every now and then when you start the truck it will act like it is out of gas... I have the smart chip in the truck, it will show the fuel trim pretty much off the chart... 25% or more during these episodes... I can not read fuel pressure (with chip) but I have replaced the pump twice with same results. After the truck clears out it runs perfect, just acts up when I start it(sometimes) the only error code is a vane error... I could use some help.... could it be the MAF sensor (has been replaced in the past) or still a fuel pump problem... thanks in advance... AJ Link to comment Share on other sites More sharing options...
sean-accstudent Posted December 13, 2004 Report Share Posted December 13, 2004 AJ, Does it feel like it is spuddering? You may want to check the fuel pressure coming out of the Injectors. Sometimes those aftermarket chips send a false reading and can cause injectors to either not have enough pressure or flood the carburator. You may also want to check the fuel filter to see if it clogged. Link to comment Share on other sites More sharing options...
dancer52 Posted December 13, 2004 Author Report Share Posted December 13, 2004 The smart chip just reads everything, it plugs into the odbII output. The truck only does this on start-up...sometimes, most of the time it runs great. Lately it has backfired thru the intake... when it does this the truck instantly runs better, kinda make me think the MAF might be the problem... who knows... thanks for the reply. Link to comment Share on other sites More sharing options...
sean-accstudent Posted December 13, 2004 Report Share Posted December 13, 2004 aj, Test it with ohm meter, look for any resistance. You might be right. Let me know what u find out. sean Link to comment Share on other sites More sharing options...
KISS_Racing Posted December 13, 2004 Report Share Posted December 13, 2004 Check the hose between the airbox/mass air meter and the throttle body. Make sure clamps are tight and plastic hose isn't cracked. Had a 2000ish chevy truck acting weird Sat. this is what was wrong with it... If your having issues with the MAF (MAP?) sensor, you should see something on the ODBII Scantool... Although sometimes you need an O-scope... Oh also disconnect the connection to the mass air meter and make sure there is no moisture... Probably not since it's only on start up. My big bet is something to do with the mass air meter since it controls the fuel mixture based on what air it is seeing... May be throwing some weird info at the computer (on key on)... If there is no mass air meter please disregard the above gibrish! sorry I didn't see this part " Lately it has backfired thru the intake... when it does this the truck instantly runs better" I really think it's something to do with the mass air meter... Sounds like it's leaning it out for a second... Although backfiring is normally a timing issue?!? Either way your computer is getting a momentary glitch... When you run the scantool, your not cycling the key off are you? Another words your not turning it off and then back on?(the truck) Link to comment Share on other sites More sharing options...
Tim Posted December 14, 2004 Report Share Posted December 14, 2004 What about your 02 sensors? For the first 2 minutes of startup (cold) these should be in a closed loop causing a rich condition. Fuel filter, plugs, plug wires, cap, rotor, air filter, etc? Link to comment Share on other sites More sharing options...
97car Posted December 14, 2004 Report Share Posted December 14, 2004 I don't know if you have tried it but use some carb cleaner and spray the mass air flow sensor also look at the tiny wires on the sensor to make sure they are no broken,the cleaning should help some,I have seen it heeelp on a 98 I recently worked on and I didn't think it was that dirty. Link to comment Share on other sites More sharing options...
97car Posted December 14, 2004 Report Share Posted December 14, 2004 You might try the air inlet temp sensor also I believe it is about $12,and is your chip setting the timing up too high?In the manual it says you cannot adjust timing like most newer ones,we tried and it haad to be set at the dealer due to the computer. Link to comment Share on other sites More sharing options...
KISS_Racing Posted December 14, 2004 Report Share Posted December 14, 2004 I have a 98 chevy 3/4 ton truck, every now and then when you start the truck it will act like it is out of gas... I have the smart chip in the truck, it will show the fuel trim pretty much off the chart... 25% or more during these episodes... I can not read fuel pressure (with chip) but I have replaced the pump twice with same results. After the truck clears out it runs perfect, just acts up when I start it(sometimes) the only error code is a vane error... I could use some help.... could it be the MAF sensor (has been replaced in the past) or still a fuel pump problem... thanks in advance... AJ Would you clarify something... When you say smartchip are you referring to the "VAT" chip in the key? Or are you referring to an aftermarket chip? The VAT (vehicle anti theft) chip has nothing to do with how it runs once it starts. It only acts as an anti-theft device... If you are referring to an after market chip, then remove it and see if it fixes your problem... I agree with 97Car, try some carb cleaner into the mass air meter... Link to comment Share on other sites More sharing options...
dancer52 Posted December 15, 2004 Author Report Share Posted December 15, 2004 No, the chip I am talking about plugs into the odbII outlet... it is just a passive monitor, I put it in to try and figure this problem out. The truck acts the same (when it is messing up) either both cold or hot... it usually happens after I am getting gas. I dont think a dirty MAF (Mass Air Flow) is the problem because it runs good after these episodes. I might look into the inlet temp. sesnsor... thanks everyone for the help... dont stop.. AJ Link to comment Share on other sites More sharing options...
hray Posted January 12, 2005 Report Share Posted January 12, 2005 AJ, Check the fuel pressure regulator. It is located on the left side of the throttle body. Pull the hose loose. If gas comes out the diaphram is broken. Unclip the regulator and replace it ($30). Be sure to get the small "O" ring out (there is a big one and a small one that rarely comes out with the regulator). Link to comment Share on other sites More sharing options...
dancer52 Posted January 14, 2005 Author Report Share Posted January 14, 2005 Thanks for the help, (did not know about the regulator) but I found the problem.... there was a small tag, like a paper price tag that was in the air intake tube, I am guessing when I started the truck sometimes it would block one of the MAF sensors. Well at least it was cheaper than a maf... sad part is this has been going on (off and on) for about a year...AJ Link to comment Share on other sites More sharing options...
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