740 & 760 740 turbo poor idle / poor start

Hey im trying to figure out how to fix or improve the engine issue on my 87' 740 turbo. its hard to start and struggles to idle at all really, if you warm it up by keeping it running it will idle aroun 500-600rpm unhappily, also has a missfire until you rev it out a little. Seems to drive fine throughout the rest of rev range, makes boost and power.

The car has a hardswitch installed for the fuel pump which you need to flick on and off to start the car... fuel mixture related? when i pulled the plugs they were destroyed by fuel carbon build up. I also investigated and noticed my b230ft engine is missing the IACV valve

btw new here 1st Volvo and I love it to bits

Comments

  • With the engine off remove the vacuum hose from the fuel pressure regulator on the end of the fuel rail.
    If fuel comes out you need a new one.
    There are a couple of different ones, pretty sure all the turbos are the same. Good Bosch one will be $200 new. Good second hand one will be $80 or so.
    The fuel pump switch was probably installed due to a failing fuel pump relay. May be prudent to have it looked at and the relay, assuming it is broken (they all brake) replaced.

    3oMhK6Lh.jpg
    xl9kVPXh.jpg
  • If your idle air valve is missing, the idle won’t be controlled by the computer so you’ll get what you get...odd that it was removed. I’d suggest trying to find a used one and fit it up like factory. Also if plugs were fuel fouled, it would be a good idea to check fuel pressure.
  • Thanks for replies.

    I checked the fuel pressure reg for leaks out the vacuum port. All good there,


    I rigged an adjustable fpr with a guage inline directly after the stock fpr. With engine off (pump on) its reading 39-40psi .

    2wncmlw.jpg

    212ybk4.jpg
  • Things I've done so far
    - redone the mechanical engine timing to stock spec tdc...
    - replaced the oil sensor wire that runs under engine with fresh wire ( it was earthing causing oil light on dash )
    - cleaned throttlebody and tps ( not sure if set tps perfect - just so it clicks as soon as you twist throttle )
    - replaced rad coolant sensor wires that were earthing.

    I plan to keep checking for exposed wires as there has been a few now. Is there a way to reset the ECU ? I don't have diagnostics either in my 87 ' as far as I know
  • I’m a bit confused by how your gauge is hooked up. It should be on the feed line from pump to fuel rail. Are you measuring it in the return line from the FPR to the tank? I can’t tell from the pics. Also I see a T in the vacuum line from the FPR...what’s that going to? Sorry for the questions but hard to see what’s going on in the pics.
  • Also cleaned oil seperator box
  • @carnut222 yeah it is in the return line in between stock fpr and fuel tank. That vacuum line goes to the aftermarket reg I temporarily installed to measure pressure . will it read correctly like this
  • Hmm, OK, if you’re reading the fuel pressure between the FPR and the tank, I’d be a bit concerned it’s so high (possibly indicating a blocked return line?) Really you need to measure the fuel pressure at the feed line between the pump and the fuel rail, but sometimes that can be difficult due to the fittings. I cut up an old fuel rail and that allowed me to make up a T that I could hook my fuel gauge up to.

    Based on your observations, I would disconnect the return line from the FPR and see if you can blow air through it easily. If not, there must be a blockage or pinch point?
    stig_helmer740
  • Ahhh OK. I can install my aftermarket fpr before the rail if need be, it just has barb fitting in and out of it. Hmm so I just took off the fuel return line to tank and tryed blowing air.. Seems blocked like you said ??
  • Ahhh OK. I can install my aftermarket fpr before the rail if need be, it just has barb fitting in and out of it. Hmm so I just took off the fuel return line to tank and tryed blowing air.. Seems blocked like you said ??

    I could be wrong but should be able to blow through it. Try removing fuel cap as it may be that if there’s no vacuum to the charcoal canister the system is sealed up.
  • Can hear bubbles at back of car near tank , blowing with fuel cap off .
  • Can hear bubbles at back of car near tank , blowing with fuel cap off .

    Well that’s a good sign. So now if you can just check fuel pressure at the input line as discussed that would be a good next step, and if you’re not doing it with the car running I guess it would be good to have fuel cap removed to get a more accurate reading. It probably won’t make much difference though if the return line isn’t blocked...
Sign In or Register to comment.