Engine stutter under heavy load

on Cabriolets 84.5 and below have a 10 gallon tank full sized spare, and a single fuel pump.

On 84.5-93  They had 2 fuel pumps and a 13 gallon tank which caused the use of a space saver spare tire.

On 84.5 and above they have a in-tank pump as well as a external pump  The 84.5-89 over here have a 75 psi pump external where as the 90's had a 45psi external pump as well as EFI vs the earlier CIS.

both the 84.5-93's had a 45 psi in-tank pump  (also called Lift Pump), this pump can fail, which can cause the external pump to over work and when that happens it can whine more than your child at bed time or a teenager.  

The 84.5-93 had an external filter ( swirlpot) on the right side of the fuel tank where you can only see the clip, while this can fail, I have never had one fail or get really fouled up.  

Now with a car that is 40 something years old, fuel lines can go bad as well as the Vent lines that return to the tank.  e10 or e15 can wreck havoc on the fuel lines that return to the tank as well as vacuum hoses for the fuel system.  Gurgling isn't a good thing, and could mean that your intank interconnect hose has failed, holed which can cause the intank pump to blow fuel to the tank versus the filter (swirlpot which acts as a feed for the primary pump, it is a sump) and can cause the primary pump to do all the lifting of fuel out of the tank.

The first time that I heard gurgling in my tank the lift pump to sender had failed (still OEM) it had holed and wasn't totally filling the swirlpot.

I have a link to a how to in the archive section on how I replace my in-tank pump.

The link is in the engine section of my how-to's link at signature line, or the link itself.

1984.5-1993 mk1 How to change your in-tank fuel pump | Volkswagen Owners Club Forum

Gurgling isn't a good thing, and could mean that your intank interconnect hose has failed, holed which can cause the intank pump to blow fuel to the tank versus the filter (swirlpot which acts as a feed for the primary pump, it is a sump) and can cause the primary pump to do all the lifting of fuel out of the tank.

As its an 81 tintop gti, I'm pretty sure it doesn't have an in tank pump, just the main exterior one near the rear wheel. I think I'll pull the rear seat and visually inspect the inside of the tank (although the tank and fuel lines were replaced in recent years). I have a new main pump I've just bought and will likely fit a simple inline filter between it and the tank. Any other suggestions?

81 tintops have 1 external pump, the tank has an internal swirlpot whose screen can get plugged up with rust.  I would also suspect your return lines for air leaks at the connections. or hoses that may have ruptured.
 but the pump could be going south and needs replacing.

Been a while as was working on another (wifeks) project.
Anyway did a visual check and look what i found. Main feed pipe from tank to pump. Looks very… kinked.
So gonna replace that and pump at the same time…

Oh that's not gonna help things.

Doesn't look like the right pipe, think some has been cutting corners, literally!

Changed the fuel pump and the badly kinked hose from tank-to-pump today.
When I turn the car over I can hear the new pump running (which is much quieter than my old knackered humming one) - but the car won’t start.
Cracked off the fuel filter and as I suspected, no fuel is getting there despite cranking it for ages.
So pump is running but not pushing fuel to the engine bay…
Now I’m Confused!


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Have you pulled the sender unit and inspected it? My Cabrio had corrosion and pin holes in the pickup pipe , part of the sender unit.

Also, have you tried cracking off the fuel line at the  fuel pump outlet, to prove it is actually pumping?

I'd consider jumping the fuel pump relay (have a search on here for how to do that) so you can run the pump constantly and then see if you are getting fuel through to the filter. You can also check as jazzydog said to see if you are getting fuel out the pump.
Is it an orignal tank? If you can drain the fuel out, remove the sender and have a look inside. If it is an orignal tank there is an in-tank filter. It is a challenge but it can be pulled out. Mine was pretty gunked up. If it is really bad it could be stopping fuel flowing out the tank at a sufficient rate.
Pump is wired up the right way isn't it?? You never know!

[mention]paceman [/mention] i turned the ignition on/off a dozen times to keep getting the pump to run to try and prime the system but no joy

I haven’t try crack off the line off to see if amy fuel is actually coming out of the pump. But before i do that, your comment about wiring - is it possible i got the wires the wrong way round? Would that make it pump ‘backwards’ (into the tank as opposed to pulling out of it). From memory it was brown wire on positive, red/yellow wire on negative.

Its a replacement tank so should be pretty clean and its a ‘81 tintop so no tank lifter pump.

I think you have the wires on the wrong way round so the pump is running backwards.

Brown wires are earth/negative and coloured wire are power/live wires.

Yes i think so too! Will try swapping and let you know. Ta very much

I looks at the picture when I replaced my accumulator but I can't see the + and - signs on my old fuel pump.

It's worth trying it 1st as the pump should twist in the holder but you may need to loosen the clamp on the fuel hose and banjo bolt so the hoses don't twist.

I happen to have a print out of the wiring for an 81 gti with me (don't ask). Having checked it red/yellow is positive, brown negative.
As Mark said on VWs brown is generally earth.
Orginally the pump wiring had different size ring terminals to match the different size terminals on the pump so you couldn't wire it up wrong. If its not the original wiring then there is nothing to stop it being wired wrong.

Thanks both. I’m fairly sure in my haste to finish I may have wired it the wrong way round (forehead slap). Busy working for a couple of days so will take another look later this week and let you know!


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You may award me Muppet of the Month.  Yes i’d got the wires round the wrong way.
Bit fiddly as id reinstalled the pump and cradle but did it.  Started straight away and new pump is basically silent compared to the old one! Did the fuel filter at the same time, although when i took it out and examined it, it did look pretty clean - which is promising.
So hoping the new pump, filter and new non-kinked tank-to-pump hose will solve the OP of stuttering.
Only a nice test drive on bank holiday monday will tell! Thanks for the advice chaps and will let you know!

It happens!
I'm equally happy to have remotely guess the problem  

gregpank said

You may award me Muppet of the Month.  Yes i’d got the wires round the wrong way.

Well glad to see you joined the crowd with the rest of us that have had less than stellar experiences repairing our cars or things.  Usually it is one of those "How could I have been so Stupid…" times over the last 60 some years of wrenching on everything from Airplanes to Zebco-rod and reels. Unlike some I readily make fun of myself, and admit to my errors, well sometimes.
 

It was sunny today and couldnt wait to see if the new pump solved the stutter. Went out for a good 30/45 mins (as it normally begins to play up after 30 mins) ... and seemed ok! Needs a bit of a tune on a rolling road but no stutter. Lets hope it stays that way! Thanks again all.

Fingers crossed it worked..