Missing In Low Revs In 1St, 2Nd And 3Rd After Fuel Pump Install

[rondofj]

Hi all,

Just installed my Walbro GSS342 in tank pump now in the dark, and I can tell u its no 1 hour job, I'm no noob, have done my own FMIC install, spark plugs etc, and I can tell u the fuel pump job I found almost as hard ..

I have a problem - it is missing - like hesitating in low rpms below 2000rpms in 1st, 2nd and 3rd, havent driven long enough to see if it misses in 4th and 5th, its just small misses and once the revs go up, it feels way more responsive than my stocko pump, revs to 7000rpm very freely, cleanly and quickly where the stock one took a while.

Why is it missing in low revs only (dosen't miss in idle at all - idle is now sort of 1000rpm, before it was 800rpm). I did a thorough job and didnt miss anything, does it need a re-tune??? I will take it to be tuned the coming weekend, it is running nistune at the mo but hasnt been tuned at all..

Please help fellas, I'm stoked AND hugely disappointed too... thanks

[rondofj]

current mods are - 3" turbo back zorst, boost controller set at 12psi, pod in cold air box, FMIC, nistune (not tuned yet) - running stock r34 maps..

Any thoughts on why its missing after the pump install?? Its not major, just a few hesitations/ jolt kinda thing then goes hard after that to redline..

I'm thinking it needs a re-tune or the pump is not able to push enough pressure at low loads..

[eightsixboy]

It wont have anything to do with the tune, does sound strange if its only lower revs and not through the whole rev range.

What pump was in the car before?

I've installed the same pump in my old hr31 and a mates r33 and never had any problems.

[rondofj]

it was the stock UNISIA JECS pump- almost the same size as the Walbro by a few millimeters, yeah mate, high rpms after 2500-3000 all the way to 7000 is much cleaner and freer to rev now no misses at all, can feel the difference and I know its not my mind playin games..

[rondofj]

Had a discussion with my flatmate, he said if its fine above 2500rpms and revs much quicker and makes more sharply noticeable power, then that has got to do with the tuning which is what I think - ie why its missing in low rpms..

[Thelen]

If the old pump had some issues keeping proper pressure for some reason then maybe it is the tune, but I'm fairly sure the old pump would have problems keeping pressure once you got on the gas even more so than low down.

TBH sounds like air bubbles or something like that, whereby lowdown the restriction is noticeable, but up high not so much. Lastly, what happens if you turn on/off music/AC/headlights, that should narrow down if it is electrical supply issue (possible if the alternator is on the way out).

Ultimately, just pay your mechanic $50 to diagnose it properly before something breaks

[SiR_RB]

get it tuned first dude then see if it still does it

[Moodles2]

Could it be the switching curcuit running the Walbro pump at 6v at low load (these are meant to be ran at alternator voltage)

[rondofj]

I was also thinking about voltage issues - man it is frustrating, was expecting it to run smooth, but yes, compared to the stock one which had dangerously high a/f of aaround 13.7 and up, I can feel a good amount more power now in the mid-high rpms and very much free to rev now - revs quick n smooth to redline - just the low rpm stutter/hesitation for 1-2 seconds which was never there..

[rondofj]

If the old pump had some issues keeping proper pressure for some reason then maybe it is the tune, but I'm fairly sure the old pump would have problems keeping pressure once you got on the gas even more so than low down.

TBH sounds like air bubbles or something like that, whereby lowdown the restriction is noticeable, but up high not so much. Lastly, what happens if you turn on/off music/AC/headlights, that should narrow down if it is electrical supply issue (possible if the alternator is on the way out).

Ultimately, just pay your mechanic $50 to diagnose it properly before something breaks

Ummm, what do u mean before something breaks - I hope nothing is goin to break with this minor? issue!

[rondofj]

btw, I had to use my old sock as the walbro didnt come with one, it has a bit of play sitting against the bracket - I'm just worried that the sock to pump connection is not nice and firm - ie there is some play as I also used the stock isolator rubber cap, can the pump operate without the sock? By play I mean u can pull the sock nozzle away a bit and see a bit of the pump inlet.. worried about this

[DVS JEZ]

That shouldnt affect it. Just means theres a chance it might suck a bit of un filtered fuel.

Do a 14volt rewirr 1st then see how it goes. Check the DIY section

[rondofj]

thanx man will try that if the tune dosent fix it, all i can say is that I am completely stoked with the positives of the fuel pump install - I expected a 0rwkw increase, but it FEELS like it has gained at least 30-40rwkw, completely different beast now, apart from 1-2 misses/ gasps below 2k rpms, after that it pulls like a train all the way to 7krpms - the response is very sharp and whack-in-the-back-strong throughout and doesn't taper off at all, now i know that the previous stock pump wasnt supplying enough fuel for my current application..

just cant wait for the tune, that should get me roughly 20rwkw or more hopefully.. love it..

For all those doing stage 1 mods - exhaust, intake, boost, FMIC, an aftermarket fuel pump is a MUST. I had always thought it was a stage 2 mod.

[89CAL]

Yeah you never said if you actually did the rewire as this is the main problem with walbros. And he means you

Might break something if there is air in the line as in it will lean or and detonate etc

Confirm you've done the rewire and it is getting 14ish volts on idle etc

[rondofj]

no rewiring done mate, mite have to do that later, but will see if the tune can yield anything goood... as i said it is only missing below 2k rpms, above that it is so MUCH better than before

[Thelen]

Sounds like you have a good plan, good luck

[rondofj]

cheers, hope it turns out well

[89CAL]

simple fact. If youve only change the fuel pump, the tune should be fine (SHOULD be not WILL be)

Do the rewire first, as it will cost next to nothing to do. Tunes are not cheap especially if you do that then find out its the pump not getting enough voltage

Or youll end up spending just as much as it would have cost for a Nismo/Tomei pump like I suggested in the first place. FYI I installed mine and the car ran no different afterwards.

Do the re-wire first

[rondofj]

thanks, I'm only getting a tune cos I just got nistune installed a coupla weeks back and havent had a tune yet, so fuel pump problem or not, I am getting a tune regardless, and will see about re-wiring - saw a write up, but theres no pics, also someone suggested I should ground the fuel pump control modulator to the chasis or something - have no idea where or what that is he he

[boostn0199]

Just putting a fuel pump doesnt increase the power in the car it just enables it to run more power just like a front mount,you will however make more power when you combine it with such mods as turbo injectors where you require more fuel to be pumped out so not sure what your talking about there.

The problem does sound strange as it is missing then working fine, would have thought it was surging from maybe mounting the pump to high but your saying it in low revs and then its fine.