The car doesn't want to rev out under load, pretty much bang on 4k in second gear and above it starts to hesitate pretty badly. I can get it to 5k if I back off a little. Other than that car idles and drives fine, although it's occasionally a bit slow to respond if I floor it from a standstill.

Things I've tried:

  • New cheapie ebay fuel pump, thought this was the issue so I replaced it with below
  • New fuel pump GSS342 255LPH purchased from TI automotive.
  • New plugs BOSCH FR7DPP seem to be the closest to OEM I can find.
  • New fuel Filter
  • New plug wires; not OEM/Bougicord but swapping back to the originals changes nothing
  • New timing belt + All acc re-timed with the special tool
  • Full tank of 98
  • Checked fuel pressure sits around 36-37 with FPR connected to vacuum at idle, Disconnected jumps to 40-42PSI
  • Flushed injectors out of the car with carb cleaner
  • New NTK MAF, no difference from OEM siemens so have siemens installed currently
  • New OEM upstream O2 sensor
  • New OEM TCS
  • 18-20"hg vacuum at idle no load
  • Boosts around 13-16PSI
  • Ebay Ignition coil - I am a bit suspicious of this
  • Ensured 12V connections at coils are firm.
  • No codes in VOL-FCR

I have noticed there is a second FPR mounted above the fuel filter next to the tank, I haven't bothered with it but is it possible this one is the issue? I would just like to replace both of them however I can't actually find any to purchase.

It feels like a fuel delivery issue but nearly everything has been replaced. I am once again scratching my head with my empty wallet in hand.

  • So in my journey I found out I had yet again made a problem to my solution.

    The fuel smell was the seal not being seated properly between the tank and fuel pump assembly causing fuel to seep out when the tank was over half full.

    The hesitation issue turned out to be the plugs. I thought that the FR7DPP30X plugs were just a 0.03" gapped version of the FR7DPP+ plugs. Turns out they are quite different and yet again I've done a silly.

    Image description

    Different ground strap shape and insulator thickness.

    Image description

    Different size of platinum tip.

    At least it's had a proper tuneup now.

Put a scope on it

See what it does (ignition) at 4000rpm

What year/motor is this one? I take it that if you rev it out in neutral, it goes past 4k no problem?

    jamesinc 1999 B4194T

    Haven't revved it out in neutral but it will climb passed 4k in first gear.

      When you say it “hesitates” what exactly does it do?
      Does it bang and cough?
      Does it misfire like a machine gun?
      Does it have a light stutter?
      Does it just run flat, so a passenger might think you have just lifted your foot off the accelerator pedal?
      Something else?

      When you get it above 4,000rpm does it run properly, or does it continue whatever the problem is?

      Have you checked the fuel pressure while driving?
      My first guess is that you might have a partly blocked fuel supply that allows enough fuel for low RPM running but can’t keep up at higher revs.

      I would describe it as a pretty severe stutter/buck, it'll fall flat then surge repeatedly but won't accelerate. No backfiring or any of the sorts and doesn't vibrate like a misfire would. It really does feel like it's running out of juice.

      I do need to check the fuel pressure under load just don't have a line long enough yet.

      Ex850R

      I have removed the internal filter basket in the pot as it would not fit on the new pump with its smaller offset inlet. The main basket on the bottom of the pot is a bit brown but didn't seem clogged at all. I did give it a good spray with carb cleaner before reinstalling it. Maybe removing the internal basket is causing issues? The other pump I removed has the correct setup with both baskets installed and it still have me grief.

        could be one of a dozen things.

        (which i realise is not helpful)

        best options are air/fuel ratio and a scope for spark. it feels like failing high tension spark, though that is just a feeling. do you have a wideband sensor available? a workshop will have one, a dyno shop is the best option.

        I do have a wideband sensor out of an old Mazda, no way of reading it though. Driving it today can definitely feel it misfiring now has that classic vibration. Checked the spark on all cylinders while cranking and cylinders 2 and 3 have a noticeably smaller spark, still blue but just not as strong. I'll order another coil pack for now but if that's unsuccessful I'll take it to a shop with the proper tools, don't have an oscilloscope or any way to measure the afr under load.

        It does sound like a fuel delivery issue to me, it could be metering but I think given it's behaving normally below 4k, fuel is more likely.

        I think get your pressure gauge extension, confirm you're seeing a drop in pressure, then go from there.

        I agree brown filter sock is nothing to be concerned about if it's clear of debris, but it's best not to assume anything, just start at the tank and work your way towards the injector until it clears the issue.

        If you start running out of ideas, it may be debris in the lines, cutting the filter open might reveal something, but as it's a new filter maybe leave that for later so you don't waste money.

        Check the plugs anyway. If they are all firing ie. all same colour. maybe colour is an indicator too if not correct. Can at least show if leaning out etc. Id ask Berry's as well , they are a font of knowledge. (Please buy something in future from them as they are always on the phone helping and so busy they dont have the time for everyting everyday!)

        5 days later

        So the coil didn't fix the issue and have to wait for a new Schrader attachment, the one I used previously was not fuel rated and the rubber has gone bye bye. Two things that I've noticed:

        1.The issue becomes more apparent when the car is hot

        1. Smell of fuel coming from rear passenger wheel well.

        Doesn't seem to be coming from the filler cap or neck so I'll check that out. I have a funny feeling it's from that second FPR mounted above the filter but I still have no idea what purpose it serves on this car as the vacuum line appears to go to the top of the tank.

        19 days later

        So in my journey I found out I had yet again made a problem to my solution.

        The fuel smell was the seal not being seated properly between the tank and fuel pump assembly causing fuel to seep out when the tank was over half full.

        The hesitation issue turned out to be the plugs. I thought that the FR7DPP30X plugs were just a 0.03" gapped version of the FR7DPP+ plugs. Turns out they are quite different and yet again I've done a silly.

        Image description

        Different ground strap shape and insulator thickness.

        Image description

        Different size of platinum tip.

        At least it's had a proper tuneup now.

        nut3y changed the title to Hesitation at 4k [Solved] .

        Well done finding it. i bet it was a relief to drive it and have it push past the 4k mark.

        The reason for the suggestion of high tension spark was your mention of the hesitation being throttle related, you said "I can get it to 5k if I back off a little." This suggested that there was not enough spark to push through the fuel/air mix with an open throttle (more air/fuel in the chamber) though it was Ok when less air/fuel.

        Now it is stable and working I would look at some genuine coil packs.

        Also those plugs are odd, I cannot find them in any cross reference to NGK - all of my books are NGK and was attempting to look them up.

        Gap should be about 1mm, factory was likely 1.1 though you have wound the boost up (more air/fuel) so a little less will probably work better.

        What was the gap of the old plugs vs. the replacements? You may find the old plugs work with a smaller gap.

        It sure was a relief

        I believe the stock gap for the OEM plugs plugs is 0.7mm with the funky ones being 1 or 1.1mm. I did gap the plugs to 0.7mm after I purchased them but they were clearly still causing problems.

        The car runs a lot better overall, a lot more responsive down low in the revs and it seems to get better fuel economy. I'm wondering if the resistance of the plugs is any different? That never seems to be specified anywhere and would be the only major difference other than the size of the electrode.

        Which ones are you referring to being odd?

        Just a thought, would timing need to be changed for the boost as well?

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