Hesitating under load/WOT

[Stian_P 0 1 Cars]

Hi.

I have a 90` 1,9 GTI with Motronic injection and a cat, 120 hp version. The problem I have is it hesitates a lot when trying to accelerate at speed, it`s also a bit more jerky off the line than it usually is.

If I try to accelerate it goes OK to about 3k RPM, if I floor it it really struggles to get past 3k RPM. It feels like it is loosing power if at WOT, compared to part throttle. It feels like a fueling problem to me, as it dosen`t misfire and the rev counter is stable.

My spark plugs are new, I changed them to se if they were a problem. Also my coil is new.

I  have a Walbro 255 pump that is about 5 years old, tested it today and it gave allmost 0,5 l in 10 sec turning the engine over. That seems a bit low to me, as it equates to about 180 l/h? The FPR is standard.

What do you guys think, do I have a fuelpump issue, or maybe the FPR is on its way out?

[PhilNW 40]

Have you checked the pump for pressure as well as flow?

 

Needs to be giving around 3 bar pressure

[Stian_P 0 1 Cars]

No I haven`t. Any tips on how to check it?

[PhilNW 40]

Tee a proper pressure gauge direct to pump outlet in first instance and run engine to see how pressure varies with engine revs.

[Stian_P 0 1 Cars]

Do you know what threads the fuel rail have? I'm gonna have a look and see what I can find, maybe a local shop have what I need. 

[PhilNW 40]

My test gauge came with tee piece/lengths of fuel hose and jubilee clips to fit push fit connectors.

[pug_ham 240 3 Cars]

What condition is your distributor cap in? 

 

I had a similar issue to this, albeit on a jetronic car, fine under light load but if you tried to accelerate hard, it spluttered like mad.

 

g

[Richard309Sri XU5JA 205GTi 7]

removed posting - misunderstood postings above 

 

 

 

 

Edited September 24, 2021 by Richard309Sri XU5JA 205GTi
mistake in reading the post

[Stian_P 0 1 Cars]

36 minutes ago, PhilNW said:

My test gauge came with tee piece/lengths of fuel hose and jubilee clips to fit push fit connectors.

Ok. I'll see what I can find next week. Thanks for helping, I'll report back when I know more. 

[Stian_P 0 1 Cars]

28 minutes ago, pug_ham said:

What condition is your distributor cap in? 

 

I had a similar issue to this, albeit on a jetronic car, fine under light load but if you tried to accelerate hard, it spluttered like mad.

 

g

It looks fine, No signs of wear or any other damage. My plugs look like New still, but they have not been in the car for Long. Maybe a bit early for signs of lean running. 

[DamirGTI 323]

Fueling/pressure problem or dirty injectors .. sounds like .

 

Simple things , fuel filter good ?

 

Is the check engine ON ? if so , run self diagnostics test .

 

D

[Richard309Sri XU5JA 205GTi 7]

5 hours ago, Stian_P said:

Do you know what threads the fuel rail have?

I have this measurement I think of the threaded connection - if that is needed 

[Stian_P 0 1 Cars]

1 hour ago, DamirGTI said:

Fueling/pressure problem or dirty injectors .. sounds like .

 

Simple things , fuel filter good ?

 

Is the check engine ON ? if so , run self diagnostics test .

 

D

I had the injectors ultrasonic cleaned 5 or 6 years ago, the fuel filter was changed about 10-12000 km ago. So I think they should be ok. No check engine light So far at least. 

The fuel pump is a pretty cheap walbro pump, dont know if they are any good? So I am thinking either fuel pump or fuel pressure regulator. Any thoughts? 

[DamirGTI 323]

Might be fake/knock off Walbro , there's fake ones all over the webshops/ebay and the likes need to shop around carefully .. obviously fake ones don't last long .

Or there's pressure/supply leak somewhere in the pump-to-housing connection .

 

Early OE Bosch roller cell pumps often last for ages (if not left unused in the stale fuel) and supply well over needed fuel volume for 1.9 engine , later Ph2 turbine style pumps not as good as early ones .

 

If you still have working spare OE pump , try it out instead that Walbro ..

 

Press. regulator - unlikely from my personal experience , they rarely go bust and also last for very long time trouble free .. just the vacuum hose/line from the manifold to the reg. , tends to split/crack/deteriorate due to age so yes check that one if it's still fine .

 

D

 

 

Edited September 24, 2021 by DamirGTI

[Stian_P 0 1 Cars]

12 hours ago, DamirGTI said:

Might be fake/knock off Walbro , there's fake ones all over the webshops/ebay and the likes need to shop around carefully .. obviously fake ones don't last long .

Or there's pressure/supply leak somewhere in the pump-to-housing connection .

 

Early OE Bosch roller cell pumps often last for ages (if not left unused in the stale fuel) and supply well over needed fuel volume for 1.9 engine , later Ph2 turbine style pumps not as good as early ones .

 

If you still have working spare OE pump , try it out instead that Walbro ..

 

Press. regulator - unlikely from my personal experience , they rarely go bust and also last for very long time trouble free .. just the vacuum hose/line from the manifold to the reg. , tends to split/crack/deteriorate due to age so yes check that one if it's still fine .

 

D

 

 

It may be a fake, I remember it was quite qheap. I guess I'll have to buy a new one then, I have found Bosch pumps for sale. Do you know if those are any good? 

[DamirGTI 323]

Certainly , Bosch pumps are well known for quality/durability they're OEM suppler/factory fit pumps on a lot of cars .. can't go wrong with them .

 

But , take the current pump out and have a look .. if the hose connection between the pump and pump housing is maybe split/leaking , also check if it's real or fake Walbro by this info : https://www.driven2automotive.com/blog/spot-fake-walbro-gss342-fuel-pumps-2017-18/

 

D

Edited September 25, 2021 by DamirGTI

[Stian_P 0 1 Cars]

I'll order a new Bosch pump, and hopefully that will fix the problem. Not sure if I have a fake Walbro, but there is no pressure in the fuel lines after I shut of the engine. Probably a fake one, considering the low price I paid. 

Thank you all for helping out, it's much apreciated. I'll let you know how it goes. 

[Stian_P 0 1 Cars]

Turns out I have a real Walbro pump after all. And of course the bosch pump diameter is bigger, about 3 mm. So it dosent fit the adaptor I got from Allenallen. So I am considering drilling the hole bigger, Just need to find a place that can do it for me. 

But the bosch pump I got, could it be for a phase 2 maybe? I have the phase 1 Black housing. 

[Stian_P 0 1 Cars]

Today I tried another standard pump I had in a cabinet, thought I'd give it a go. It made a tiny squeel when I startede cranking, but after the engine came to life it buzzed away quite happily it seemed. And best of all, it cured my problem. No more hesitation at acceleration.

I Just hope the pump Will keep working, and it Will be happy days from now on 

 

Thanks for youre input guys, much apreciated.