1997 tahoe, shuddering at highways speeds - Page 2 - Off-Road Forums & Discussion Groups
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post #11 of (permalink) Old 02-01-2004, 08:59 AM Thread Starter
 
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Re: 1997 tahoe, shuddering at highways speeds

Hey BigRed,

the plug wires are right, an the firing order is correct.

it did it before and after replacing them.

besides, it wouldnt pull hard when you stomp the throttle like it does now.

I think I will drive it a bit today, and then pull the plugs in order and see if I can narrow it down to one plug that looks different.

otherwise im at the mercy of someone with a better scan tool than the autozone junk..

thanks for the help!


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post #12 of (permalink) Old 02-01-2004, 09:24 AM
 
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Re: 1997 tahoe, shuddering at highways speeds

I dont often put all of my eggs in one basket like this, but I would bet my ass your problems lie in one simple little unit....



If your experiencing an intermittent and random cylinder misfire, there is one of two things wrong.

1. Your fuel injectors or pressure regulator are plugged and/or leaking. Common problem, most trucks your age need these things right about now if not sooner.

2. Your 'new' fuel pump is not delivering the proper pressure to the poppet nozzles to make them open enough to do any good. I just did a write up on poppet valves over at MCT.com. Heres the link if you would like more info and another picture of your manifold with the meter body in it. Poppet Valve Writeup

Like I said, normally I would suggest other things first, but this seems to make sense to me considering all other things you have already done. Knowing that you had a new pump just put in also throws up a red flag to me. One last question... what brand pump did you put in there? Just curious.
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post #13 of (permalink) Old 02-01-2004, 10:23 AM Thread Starter
 
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Re: 1997 tahoe, shuddering at highways speeds

the pump was an autozone special, the only place in town that had the pump in stock, the day before thanksgiving, 500 miles from home.

I bought the entire assembly, $180ish.

if it isnt delivering enough pressure how come if you floor it the truck never skips a beat? and pulls smoothly to 100+ MPH?

as bad as I would hate to replace that fuel pump I would be happy to solve the problem, but I am not following your logic there.

thanks for your advice, Im off to read the link stuff you posted.

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post #14 of (permalink) Old 02-01-2004, 11:07 AM
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Re: 1997 tahoe, shuddering at highways speeds

Well anything auto zone sells is a piece of junk!!!
post #15 of (permalink) Old 02-01-2004, 12:40 PM Thread Starter
 
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Re: 1997 tahoe, shuddering at highways speeds

like I said I didnt have much choice, I could have ordered one from another shop, and waited a couple of days, but it was raining and cold there, and I had plans for 2 other family gatherings in 2 other states.

its easy to say its junk, but how do i prove the fuel pump is the culprit?

I just drove the truck again, it drove perfect for about 10 minutes, and the SES light even went off.

then on the way back home it started missing again.

I checked the coil again thinking maybe it changed as it warmed up, it still tests within spec ( almost the same as tested when cold).

I found this coolant leak on the top of the manifold also, could this somehow be related to my problem?
check photo.

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File Type: jpg 1256432-leak.jpg (49.9 KB, 18 views)
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post #16 of (permalink) Old 02-01-2004, 10:30 PM
 
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Re: 1997 tahoe, shuddering at highways speeds

Ozark that leak appears to be coming from your water heater hose in the center of the pic. I just fixed mine 2 days ago. I bought the entire fitting from Autozone (I prefer Autozone) for $13.00 and replaced it. I didn't have time to see if only the innards were available so I bought what they had. When taking off the old fitting, it broke on me and I had to use an EZout to get the rest of it out. The only way I can see that leak causing your issues is if the coolant was getting down to the spark plugs and grounding it to the engine block. It's possible, just 2 weekends ago, I cleaned a friends engine in a Nissan and after I started the vehicle, it started missing. I found water in the holes where the plugs are at. I dried it out and all was fine after that.

That's all I have for you. Good luck with your issue.
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post #17 of (permalink) Old 02-02-2004, 06:36 AM
 
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Re: 1997 tahoe, shuddering at highways speeds

I'm with krayzie on this one. after all the ignition is taken careof then you're looking ata fuel issue. and my susposition is that its i nthe fuel delivery system. and the quality of scanner means nothing. the snap-on scanner we use at work does about the same thing as the autozone scanner. it'll say random cyl. misfire too.
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post #18 of (permalink) Old 02-02-2004, 07:45 AM Thread Starter
 
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Re: 1997 tahoe, shuddering at highways speeds

ok, so IM driving it this morning, wife wasnt back in my car yet, so Im taking kids to school in her tahoe.

its missing all teh time, barely move out of its own way, even when I mash the gas its not 100% now.

the check engine light came back on for a while, then started flashing then stayed on steady.

I hate this truck.

SO If I goto GM and have them diagnose, I am going to pay $79 for them to tell me its a random multiple cylinder misfire?

How do I fix the fuel delivery problem?

is it the cheap fuel pump? dirt in the poppet valve(s)?
are there any of those pour in the tank cleaners that do any cleaning at all?

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post #19 of (permalink) Old 02-02-2004, 10:42 AM
 
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Re: 1997 tahoe, shuddering at highways speeds

To to autozone again, they'll check the codes for free, and you can look at the repair manual codes on their website [img]images/graemlins/40BEER.gif[/img]
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post #20 of (permalink) Old 02-02-2004, 10:52 AM
 
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Re: 1997 tahoe, shuddering at highways speeds

yup, verify once again that its a random cyl misfire. then to test the fuel pump you'll need to borrow or purchase a pressure gage. you can then test the pumps pressure at the fuel rail. there is a schrader valve on the drivers side of the intake and a bit towards the firewall. that can rule our or confirm the fuel pump. after that, fuel pressure regulator. as far as the intanl cleaners, the only one that ever seemed to do anything for my vehicle was the valvoline synpower in tank cleaner. costs about 4-5bucks.
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