4.3L Intake work

So, the S10 has been having a lot of trouble starting recently.  It’s only an issue in the morning, after sitting for many hours.  Once the truck fired, it ran like a top.  Plenty of power, no hesitation or stuttering, so i was pretty sure the fuel supply was good to go.  Just to be sure, several months ago I replaced the fuel filter.  No change.

There were two options.  It was either the Fuel Pressure Regulator, which is known for failing and allowing fuel that is in the lines to drain back through the fuel return line to the fuel tank when the machine sits overnight.  There’s also a check valve in the supply line that could be leaking allowing the fuel to drain back down that path to the fuel pump.

Now, because I could prime the pump by turning the key on (not start), and I could do this five or six times without improving the starting capability, I was pretty sure it was on the return side of the fuel meter body rather than the supply.  SO, I bought a fuel pressur eregulaqtor.

Guess what?  The FPR is INSIDE the intake manifold.  Yup.  Not on the firewall like a normal car, but underneath the “upper  intake manifold.”  To get there, I had to pull the entire harness off, plus a bunch of other crap.  IAC, TPS, A/C clutch and control lines, EVAP valve, PCV line, crankcase vacuum.  Coolant temp sensor line, three brackets, 10 bolts and studs.  Three more to pull the throttle body off.  That’s after the two sensors on the intake tube (MAF, IAT?) and the entire intake system.

Okay, so I got it all pulled off.  Then the six injector/poppet nozzles come off, and the fuel meter body itself, complete with six injectors and fuel pressure regulator.

What the crap kind of fuel injection system is this, anyway?  Ridiculous.  Little tubes that go to the intake runners.  I can’t WAIT to get the fuel rails from the LT1 on there.

Anyway, you pull that monster (spider) off, and pull the FPR off of it.

Here’s lookin’ down the barrel of the FPR.

Here’s the spider:

And here’s the inlet to the fuel meter body.  At teh top is the fuel inlet and return connections (where the NUT KIT on the older system is installed):

Okay, so you get the FPR out, the new one in, and you reassemble, no problem, right?  Yeah…

After I had reassembled everything, I had to prime the thing like ten or fifteen times again.  Once I got it fired, I had all kinds of idle issues.  It would slow down, almost die, cough, sputter, then shoot up to 1500 RPM or so.  Something’s not right.

That was last week sometime.  Tonight, I fired it up, and had to prime it a bunch again.  Once it was running, I realized that there was a pretty loud sucking sound, and a really bad vacuum leak would behave that way.  So…

I pulled it all apart again.  Sure enough, the seal on the Fuel meter body.  I pulled as much out as I could, but I’m not sure if I got it all.  There might be 1/8″ or so left in the intake runners somewhere….  Nothing I can do now.  It’ll either combust and blow out, lodge in an intake valve, or I already got it.  Who knows.  Ran to the auto parts store, got a gasket kit, tossed the new meter body gasket on.  SWince it only came as a kit (30 bucks), I swapped the UIM and TB gaskets too, and coated everything with a liberal slap of carb cleaner as well.

Add beer.

NOM NOM.

Here’s what I pulled out:

Eeep…hope most of it came out.

So it fired up on third or fourth crank this time, which is AWESOME.  There will be some air in the lines when you start it the first time, so I’m not too worried about it.  True, I had it fired earlier in the night, but I also relieved the pressure when I broke the fuel connection.  Ran great, nice little purr idle.  So either I’ve got it fixed, or I need to upll the fuel pump.  Which is in the tank.  Which is beneath the bed.  I sure HOPE it was the FPR….

Meh..I need to put a Walhbro in it for the LT1 anyway.

I’ve had a couple guys ask me why I’m bothering.  Eventually, I plan on selling this 4.3, which is in great shape for 140K miles.  The tranny is freshly rebuilt.  I’d hate to have something like this be a problem for whoever buys it, and it’s relatively easy to fix so that I can say, “Ran great when I pulled it!”

I’m going to let it sit tonight and get completely cold, and see if it cranks as easily in the morning.  Wish me the best!

Some more pictures!  Here you see my GOGO juice, along with everything I’ve replaced so far.

You can see both temperature senders (one for the gauge, the other for the PCM), the old FPR, screen, O-ring, the UIM gasket, and TB gasket.  I did NOT replace the exhaust header gaskets.

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9 Responses to “4.3L Intake work”

  1. Jason Says:

    I have a question when you removed the fuel pressure regulator was there a vac hose connected to it and where did it go to I have the same engine but I can’t find this so called vac hose thats supposed to connect to my fuel press. reg, I hope you can help Thanks Jason

  2. Jason, I didn’t have any vacuum lines in there. Why do you think there should be one?

    From what I understand, the FPR controls the fuel delivered based upon intake vacuum, and so if you’ve got an FPR mounted on the firewall (like most engines), then you need to drive it with a vacuum line. This is also true for forced induction engines.

    With THIS FPR however, since it’s mounted on the fuel metering body, the “downspout” looking thing on the FPR is INSIDE the upper intake manifold, which is at the correct vacuum. The whole FPR, actually, resides at engine vacuum, so you don’t have anything to connect it to. As vacuum changes with engine RPM, it delivers more or less fuel.

    If anyone knows any better, by all means, post up. This is partial speculation on my part.

  3. Stephane Says:

    Thanks for the picture and procedure.
    The 4.3L on my 1997 Sonoma is having the same issue (won’t start when cold, and terrible fuel economy).
    I’ll replace the fuel pressure regulator in few days, and I’ll keep you informed !

    Stephane Fontaine

  4. Stephane,

    Let me know if I can help at all. Please note: it was actually the fuel pump that was going bad on my truck. After I replaced the FPR, the problem got a LITTLE better, but by no means was it solved. It wasn’t until I replaced the fuel pump with a AirTek/Walbro that the truck started up on every crank. Runs like a champ now though!

  5. Stephane Says:

    Hi L-T.
    I must tell you that english is not my native language, so I’ll apologize for any mistakes I’ll make !

    I did remove the upper intake manifold (plenum I think ?) without any problem.
    I was supprised to see how much dirty it was inside. A lot worst than your picture !
    I tried to clean the outside of a poplet by removing the plastic case at the end, and I broke it. So I asked the price for a complete “spyder kit” at my local GM dealer, and it was more than 1k $ (the regulator itself is 142.50$, ridiculus !).
    I was able to pick up a used one at my local scrap yard (not sure of the exact english name) for 100$. I had to remove it myself from a blazer, and the inside of the upper intake manifold was dirty too, but not like mine (let say between your’s and mine). So I asked myself: could it be normal that the inside of the upper intake manifold gets dirty with time ? They’re must be “residual vapor” of fuel when the engine is turned off, and those vapor could rise up from the intake to the upper intake manifold where it will eventualy dry, and leave a sticky black stuff ?

    Anyway, I was around 12 MPG before, and I’m 17 MPG now with the new “old” spyder assembly, so it was not a bad move !

    Unfortunatly, the truck is still not starting “perfectly” when it’s cold. I was able to start it yerterday without adding “quick start fluid”, but it was difficult.

    I looked for a fuel pump replacement, and the best deal here was a new fuel tank with the pump already installed inside (380 cdn$). Is should cost me around 550$ installed.

    I’ll keep you informed ! I want my truck to start like a champ too because I bought it this summer, and it’s eqquiped with a snow plow. And a snow plow truck MUST be able to start in the winter !!!!

    Stéphane Fontaine

  6. Stephane, your English is just fine. There are plenty of Americans who can’t communicate as well as you can in the only language they know, so don’t worry about it!

    Yes, the intake plenum can be quite dirty. If you look at the intake I pulled off of my LT1, it was filthy. This is due, I believe, to the EGR system–exhaust gas is sent back into the intake manifold to be reburned for cleaner emissions. This brings soot and other combustion products into the intake, which coats the insides of it. Surprisingly, it’s the usually right under the fuel pressure regulator or the injectors that is the cleanest in the 4.3L from what I’ve heard–the clean fuel coming in from the tank cleans the system if it just drips down after the engine is shut off (or as it sprays and isn’t immediately burnt). Also, if you use quick start fluid often enough, it can be damaging–it causes a very hot burn, and can remove protective oil film in the engine prior to engine start. It’s fine to use on occasion, but if you use it as often as you start the truck, it may cause damage. Of course, the only solution is to get the truck running, so…you do what you have to do!

    Fuel pump replacement is quite a pain. I went with a Walbro because I was eventually going to the V8; even if you get an original equipment/Chevy replacement, you won’t save that much money. Be very careful removing the old one, because if you can save the fuel basket (what the pump sits inside), you can only replace the fuel pump itself. I’ve seen those go for much less–about $150, if I remember right. Unfortunately, as I was removing the fuel basket from the tank, I broke one of the fuel line connectors (stupid plastic!), so I had to replace the basket as well.

    Strangely, I have no pictures posted. I’ll see if I can find some tonight. Relevant posts (1) and (2)

  7. Yeah, also?

    S10 with a snow plow: VERY awesome.

    a snow plow truck MUST be able to start in the winter !!!!

    So true, so TRUE!

  8. Stephane Says:

    Hi L-T !
    I had my tank & fuel pump replaced last week, and it did cost me a lot of money !
    380$ for the fuel & tank, and more than 250$ of labor !
    But it was worth it !
    My truck is starting like a new one now !
    I’ll send you some picture of it with the snow plow if you want !
    stfontaine @ hotmail dot com if you want pics !

    Thanks !

    Stephane

  9. email sent! Glad it got running, even if it did cost so much. That’s the problem with shops–they want to earn money for their work!!!

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