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K30 TBI problems solved!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BadDog, Jan 18, 2002.

  1. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    I found out what was causing all the whacked out problems I've been having with my TBI. The fuel pressure was too low because the rubber isolator line in the pickup had a hole in it. I don't have a test gauge so I checked when I first got it together by cracking a line open and seeing that it had quite a bit of pressure and that it held pressure when the key was off for at least 30 minutes or so. This was all part of pressure testing my hand made hard lines. Well, it looked good when I put it together but, apparently the rubber line was weak. When I looked at it today, it was soft, spongy, split all around the ends, and had one nice little hole in it that you could not see unless you flexed it a little bit. While in there, I changed the pump, sock, and the filter. Something else I've never seen before, the filter was broken loose INSIDE! Just flopping around in there not filtering anything.

    With a new pump and filter, I no longer have the surging, backfiring, OR the EGR problems. Man, wish I had gone on and gotten the under hood pressure gauge that goes in-line rather than waiting and trying to find a cockpit mounted gauge like I want. Sure would have saved some time.

    So, lessons learned from my wasted time. If your gonna mess with fuel injection, you MUST have a pressure gauge!

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  2. Hossbaby50

    Hossbaby50 3/4 ton status

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    Congradulations. I am happy to here you found the source of your problem, and hope to see you on the trail again sometime. It was nice meeting you and your kids. Good luck with the rest of the project.

    My Chevy isn't broken, its just out of gas.
     
  3. thatK30guy

    thatK30guy 1 ton status Premium Member

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    I know what you mean, Russ.

    There's nothing like that feeling of figuring out something that makes your truck run better. [​IMG] That feeling of accomplishment is very self-rewarding. [​IMG]



    <font color=red>Only real men drive K30's!!!</font color=red> [​IMG]

    <a target="_blank" href=http://coloradok5.com/gallery/thatK30guy>The K30 Collection</a>
     
  4. Greenblazer-AZ

    Greenblazer-AZ 1/2 ton status

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    Hope to se you on the next AZ run!

    If you knew the truth, you too would be against marijuana prohibition!
    Blue '74 K5 Blazer Topless W/ 35 BFG Muds (See profile for pics)
     
  5. DesertDueler

    DesertDueler 1/2 ton status

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    Glad you got it figured out. Let me know when you want to take it on a "small" run to check everything I will be more than happy to go out. BTW check your e-mail or PM.

    86Jimmy 4"&35"MTRs,87 burb 4"&33"MT,69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  6. TheGeneral

    TheGeneral 1/2 ton status

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    Just what is the pressure for a 350 TBI. I have an 89 350 and going to do a new pump filter screen and in-line pressure, wondering the pressure range? Debating going to in-line electric pump for secondary, good idea or not? THanks.

    If you ain't hurt, you ain't playin' hard enough.

    The General
     
  7. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    The line pressure at the throttle body should be between 10 and 13 PSI for a TBI 350.

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
    <a target="_blank" href=http://coloradok5.com/gallery/project_T2> tRusty pics...</a>
     
  8. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    12-15 psi generally. I'm told the TB can deal with pressures up to about 20 psi to give a bit more fuel (to handle hotter cams, headers, etc. without swapping injectors) but that it should never go above 20 psi to avoid popping things. I'm new to TBI so I can't say exactly how that over-driving the pressure works out, I've just seen references to it on several web sites, you know how that goes...

    As for the in-line pump, I prefer in the tank because they are cheaper and, I am told, they have a longer MTBF (mean time between failure). Only problem is that swapping them is a pain unless you make some body mods to get at it without dropping the tank (that's what I would do). As far as a *secondary* inline pump, I have no idea how that would work out. The only way you would need an in-line regulator is if you go to a higher volume/pressure pump that will go over 15 psi (up to absolute max of 20).

    There are several here who have much more knowledge than I do about TBI, and EFI in general. Maybe they can help. Hehe, my level of TBI/EFI/ECM knowledge right now is at about the same level as the GM 4x4 knowledge of the guys who keep asking if a 35" tire will fit with a 4" lift... [​IMG] Hey, ya gotta start somewhere! [​IMG]

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  9. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Actually, I should have said, 12-15 is the stock max. One of the repair manuals I was reading lists those values as a check point, "if it is higher than that, you have a bad regulator or restriction in the return system" kinda thing. I just looked in my brand spanking new GM EFI book which says that the recommended target pressure is 9-12 psi. So, Rene's info is closer than mine. Like I said, I'm an EFI newbie. [​IMG]

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  10. Twiz

    Twiz 1/2 ton status

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    Glad you got that sucker figured out..Kinda' odd problem.

    Now whats next?

    <font color=white>.</font color=white>Eric
    <font color=white>.</font color=white>Twizted
     
  11. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Next, lift and tires. Just got to get all the pieces together. Then, I gotta get the main body/cage/bed/frame stuff done. That may take a while. Tank has to move to make way for the shorter wheel base. Thinking about just turning it sideways across the rails as a first stage. Then I can shorten the wheel base and fab a simple flat bed behind the tank and battery. I would kinda like to put the tank (or tanks) at the extreme back, between the rails, to get some weight on the rear axle. But, that requires more fabrication than I have time or equipment for right now. Right now I'm just focused on getting some tires on this thing and doing a short local "test run" with some of the guys out here.

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  12. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Oh, and talking about "odd" problems. The "N" EGR that I have will hold a vacume just setting there. I bought 2 EGRs new (both "N"s) and they would not hold a vacume at idle. If you remember though, I didn't think to check either one until it was mounted and I thought they had both blown right away (or both defect, what are the odds?). Anyway, I got another one from Doug (AZBlazer) which was also an "N" and would not hold vacume at idle. I put that one on, just for grins, and it didn't help the surging problem (which of course turned out ot be the fuel pressure leak). That one is still on there now and working fine, even though it won't hold a vacume. I was wondering if that had to do the "N" (negative exhaust back pressure bleed valve) being "normally open". However, Doug also looked it up in his book which said that it should be able to hold a vacume and lists a vacume test as part of the test procedure for "N" valves. I have no clue what was up with the EGR story...

    All I know is that I replaced the pump and filter (the real problem was the leaking rubber line on the pump) and it runs like a champ. If I get real energetic, I might switch my old "holds a vacume" EGR in there just to see what happens. All I can say is that, what appeared to be an EGR problem earlier, and seemed to be cured by plugging the vacume to EGR line, must have been the early warning signs of the fuel pressure getting low. That's my best guess anyway. I can understand the surging being low pressure, I but the EGR has be baffled. Heh, I had almost convinced myself that that the surging was the IAC because of the really high IAC counts I was getting. Or maybe the ECM was bad/confused (WinALDL showed the other sensors to have reasonable values as best I could tell) and giving the IAC bad commands.

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     

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