Switches back to petrol

[allante]

I have a problem where when the car switches to gas, as soon as I put my foot down there is a flat spot and it goes back to petrol like it's run out. If I keep switching it back and don't put my foot down it eventually runs fine on gas, Like it's needing to build up pressure.
1998 Cadillac Seville
Zavoli multipoint.
It used to work fine but seems to have become worse.
Any help appreciated

[classicswede]

2 possibles that spring right to mind

sticking vapouriser solenoid
gummed up injectors. The matrx injectors are very well known for getting a bulild up of heavy ends and struggle to work untill they have fully warmed up.

[allante]

This problem never really went away, I will describe the symptoms a bit better.
I start the car on petrol no problem and it changes to gas with out a problem, I stop at the shops buy some milk, get back in the car, starts on petrol, just as I pull out into a busy road switches to gas and no power, I have to switch it back to petrol to save my life.
I then turn to gas and it is like it has run out, no power and switches back to petrol if I put my foot down, this goes on for about 30 seconds and then runs OK.
I have the software and link cable but couldn't see anything strange there.

[john_d]

has it ever been serviced? you say u have the cable and software and nothing seems strange - what have you looked at that seems normal?

you've put up with this problem since january at least, why haven't you had someone look at it? think of the money you've wasted on petrol since the problem started.

[Tubbs]

It does seen to be exhibiting signs of a sticky solenoid. When this happens what is the 'press gas' reading ?

[allante]

The car was off the road for a lot of the time, Also once it goes over to gas it's fine, for example If I leave my house and drive on a big long trip it runs on gas all the way, it's a bit annoying on the small start stop trips. I will have a look at the pressure when this happens.
Thanks

[Tubbs]

My hypothesis is this :-
Stick solenoid/solenoid coil.
First thing in the morning it will get up to temp and drive fine. If you do a long journey it's fine as the coil is energised all the time.
Stop/start energised/de energised coil = low gas pressure. System beeps as if it's run out of gas and switches back to petrol. It's got gas in it. Just not able to open pull the plunger up the tube and hold it there. Either due to a gunk on the shaft or the solenoid coil breaking down. Now the system (depending on how old it is) should be able to diagnose a coil problem. But not necessarily a sticky solenoid plunger. However they don't always diagnose a solenoid problem either.

[rossko]

Gummy reducer (regulator) behaves similarly to gummy solenoid, but with added possibilities of going overpressure sometimes. Using your diagnostic software by monitoring pressure would be useful. Identify the reducer model.

Pressure sensors can go wonky with similar effect. Identify the sensor model.

Gummy injectors are I feel less likely - they would indeed run pants, but not usually tip the system back to petrol

[allante]

Hi, I connected the software and monitored the gas pressure. It was around 1.5 before and after the switch over although it did pop up to 1.9 for a second twice. Now when I turned it back to petrol and then back to gas it would stay at 1.5 until I put my foot down and then it would plummet right down to around 30, and of course there was no power like when it's running out, If I continued to push the accelerator it would switch back to petrol, but if I just continued to ease off the power for a few seconds it would go back to normal. I switched back to petrol and then to gas around 5 times and it behaved the same each time. However on my 4 hour drive across the country it was fine.

[rossko]

No answer to "ever been serviced", so clagged filters are on the suspect list. That can include a vapour filter awash with wax, which will give temperature related efects.

[allante]

It's not been serviced while I have had it but it's been off the road most of the time.

[Tubbs]

I would change the filters before going any further.