Technical Boost levels, sensors & solenoid issues!

[PETR0LHEAD]

Hi all

having done some minor servicing, i came across some boost pipe that appeared to be hanging free, and hopefully these were replaced properly as in my other recent thread "where to stick this"

however, the car drives crap, very poor acceleration, and at over 3000rpm, i get engine warning light and limp mode.

this is diagnosed as the Overboost Sensor receiving very low signal, which figures because i then plotted a graph to measure desired boost against actual boost, and i'm always down by around 40-50% according to multiecuscan readings as pictured.

something clearly isn't right!

 

[widemouthfrog]

I mentioned in the other thread that I had had a problem that turned out to be caused by one of the short pieces of rubber tubing that the hard plastic pipes push into. Well, the symptoms you now describe are exactly the same as the problem I had. You can clear the engine fault with MES, but if you put the engine under load, it comes back on again at about 3000rpm and puts you into limp mode. I had the MAP sensor replaced (as that was what the fault was, I was told) & it made no difference. Cleaned the EGR - no change. Took it back to a local specialist & whilw he was digging around, he noticed one of these shortvbits of rubber tube looked a bit tired. He replaced it with a piece of fuel pipe off an old carb and it was problem solved. On closer inspection, the old bit of tube had perished and got a split in it that ran about a quarter inch from one end. That was enough for me to lose vacuum apparently.

I know that one of your pipes was open to atmosphere, so the circumstances are a bit different. Perhaps someone pushed somethingbdown it to block it up? Whatever - I'd check all the small-bore pipe connections. Make sure the rubber pieces aren't perished & that all the rigid plastic pipes are pushed well into them.

Something that would be very useful for this is a diagram of all the vacuum pipes showing what-connects-to-what.

 

[PETR0LHEAD]

yes that diagram would be excellent, but the best there is was what you posted from eper i fear?

the boost pipes down to the solenoid valve and actuator were my mornings target, weather permitting!

i'll try to add some pictures and findings tomorrow if i can get an hour on it.


thank god my multiecuscan is back to behaving, best money i've ever spent that is!

 

[PETR0LHEAD]

first findings, no vacuum present at the boost control solenoid

second findings is that the red vac line down from the solenoid to the vnt actuator is sound, and just mouth applied sucking pulls the vnt rod down and holds down, so the vnt is free and there can't be a leak in that line.

thirdly, the vac line that was T'd straight from the large vac pump hose that was hanging free and disconnected does have vac on it, so pump is working.



its got to be something to do with the connections round the back of the engine, probably on that Vacuum Tank, but i'm buggered if i can find an adequate routing and connection picture!

 

[PETR0LHEAD]

ok, a little deeper and im slowly learning whats what.

see here, item number 2, is Flow Modification Valve, and is linked to the throttle potentiometer circuit. Disconnecting it brings up this fault P0638


it is attached to the Vacuum Tank, and i believe looking at the eper picture, it should be linked by hose to Flow Modification Valve by the short rubber elbow
pipe.

i'm not sure yet how the vac lines interact via this valve with the boost levels, but i'll keep going.

i wonder if im not getting vacuum back to the boost solenoid from the return pipe because the vac tank is damaged and leaks it out?











finally, on the throttle body, there is a diaphragm looking device, with a vac/pressure line on it, do you think this should have either vacuum or pressure on it, right now it has nothing?

 

[PETR0LHEAD]

Ok, we are back to running again, and with full Choo Choo boost that follows the desired boost very well plotted on multiecuscan.


after checking everything else, there was only one thing left to do, and that was to inspect the Vacuum Tank mounted at the back of the engine. What a ball ache, but proved to be the clincher.

There was a historic broken spout repair (bodge!) that must have been leaking vacuum, hence the returning line to the boost solenoid had none. You can see the brake pipe sticking out the hose elbow and the glue that was supposed to hold it in there!

once i'd got the tank out, i re-plumbed it temporarily in the hope that someone could possibly compare the routing and connections to their own, just to see if mine was correct in the first place, so here it is very roughly mapped out

There was no way i was going to put the tank back with a dubious repair on the back of the engine, so i decided to repair it as best i can, but make it accessible, but if the repair fails, vac drops, boost falls, then the boost sensor trips limp mode and the miss's gets pissed at me! ha ha!

so i relocated it to the front and totally re-plumbed it in a far more reliable manner, by making the boost control side independent of the vac tank, and supply the boost control solenoid directly from the T'd vac pump line. The wiring for the Flow Mod Valve was extended to come around the front too.

The throttle body diaphragm now feeds the vac tank, which is enough to keep the Flow Modification Valve happy, and that is all it has to do now.

and this is the tank taking care of just the Flow Mod Valve.

Running like this the car is back to normal, in fact it may actually be boosting a little better than before which lets face it, they could do with a little help!

I've done around 50 miles so far with this set up, mixed driving and so far so good,

fingers crossed for the future

 

[widemouthfrog]

Crikey, you don't mess about!Great post PH. What type of tubing did you use to extend things?

Though problems vacuum_related are often posted here, I think this is the first time I've seen mention of the vacuum tank.

 

[BikeDoc]

Nice work!
If it's not too much trouble, do you think you could draw up a simple schematic for this?
Would be handy to have this topic 'Stickied' as well, for future reference.

Thanks.

 

[glowplug]

What year is your car ??? My 2003 JTD doesn't have any of that.