Hesitation at 4k [Solved]

nut3y · 2024-03-20T09:29:36+00:00

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...

nut3y

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.

dmc

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.

nut3y

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.

jamesinc

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.

Ex850R

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!)

nut3y

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

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.

nut3y

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.

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Different ground strap shape and insulator thickness.

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Different size of platinum tip.

At least it's had a proper tuneup now.

dmc

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.

nut3y

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?

Ex850R

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

nut3y

Ex850R It shouldn't be running anything over stock boost, haven't played with this one yet. There is a good chance that the gauge is out a PSI or two as it's been dropped.

Ex850R

Any change in cylinder pressure surely needs a change on when to spark ?

nut3y

Ex850R At higher than stock boost levels it would need to be changed. The ecu maps should have everything in their tables depending on the current load/boost situation. You would think that the flame propagation would be slightly slower in denser air so I don't understand why you need to retard timing when increasing boost unless it has something to with cylinder temps.

Ex850R

nut3y

Yeah i dont know , but i guess proper measuring is the way with this stuff so exhaust gas analyser etc etc.

nut3y

Just thought I'd add some findings on here.

Get some name brand coil packs Delphi, NGK, Bosch etc. The cheap ones either don't last or experience issues at high boost/lower rpm. You buy cheap, you buy twice.

Replace the injector seals. The old ones become flattened at the edges and don't seal properly with age, this has helped with some minor boost fade issues I was having and has sorted the occasional rev dip after coming off the accelerator.

Pack out the hole in the wastegate actuator rod with something that won't melt, not so much that it can't pivot but enough so there isn't a bunch of slop. The hole becomes elongated and that minor amount of play seems to affect things.

Drivers side engine mount has a little piece of plastic that can be removed with the mount out of the car. Solved heavy steering wheel vibrations at idle. I'm sure it's important for something but I haven't run into any issues yet.

Edit: Posting this in case there's anyone else running into the same issues I did and desperately searching forums for months. Thought the spark plugs resolved the issue but they had not.

The issue appeared to be the the FPR mounted by the fuel tank. The little screen on this had had become clogged with gunk despite being after the fuel filter. Cleaning this I believe has resolved the issue for good. The car didn't show a lack of pressure at the rail surprisingly but she goes how she should now.

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