1800: 1972 pv1800es

[Othen]

Originally Posted by john.wigley

Sounds a good day's work, Alan. Dodgy fuel gauges seem to be something of an Achilles' heel on old Volvos. We ran our last 745 for years by brimming the tank, zeroing the 'trip', and refuelling after 250 miles. We also carried a gallon can as the 'braces', but never needed it ourselves, although it did help a few folk out over the years.

Regards, John.

I'd been carrying a spare can - just as well. Unfortunately the speedo doesn't work either at the mo, so I can't even use the mileage method John :-)

Alan

[c1800]

“ I removed the 6 machine screws and took it out: what a horrible sight! Stuck in place and covered in rust (I suspect the car had been stored empty of gas for some years)”

Volvo said they were good for 11 years...

Following with interest!

[Othen]

Originally Posted by c1800

“ I removed the 6 machine screws and took it out: what a horrible sight! Stuck in place and covered in rust (I suspect the car had been stored empty of gas for some years)”

Volvo said they were good for 11 years...

Following with interest!

Really? I rather suspect the item was 50 years old, but amazingly still seems to work fine after a good clean up and freeing off the fulcrum. Unfortunately I forgot to take a photo of the float/sender unit, but it was horrible: covered in surface rust and I'd say it had not moved for about a decade.

It will be a real win if this fixes the problem at no cost (I like free or cheap fixes). It will be a huge bonus if the feint whim of petrol is cured by the new gasket I made to replace the fossilised one :-)

Alan

[Othen]

A question: At start up the fuel pump in the back of the car operates properly - when one switches on the ignition it spins for a few seconds to pressurise the system. When driving Delores back the barn in which 'Janet' stores it yesterday I thought I heard the pump operating continuously. I don't know whether this is correct, or whether perhaps there should be some sort of control system that regulates it.

Before I go looking for a problem that may not be there, would someone let me know whether the fuel pump should operate all the time when the engine is running?

Many thanks,

Alan

[Laird Scooby]

Originally Posted by Othen

A question: At start up the fuel pump in the back of the car operates properly - when one switches on the ignition it spins for a few seconds to pressurise the system. When driving Delores back the barn in which 'Janet' stores it yesterday I thought I heard the pump operating continuously. I don't know whether this is correct, or whether perhaps there should be some sort of control system that regulates it.

Before I go looking for a problem that may not be there, would someone let me know whether the fuel pump should operate all the time when the engine is running?

Many thanks,

Alan

Yes Alan or the engine would stop. There is a Fuel Pressure Regulator (FPR) under the bonnet which adjusts the line pressure according to load. As the ECU alters the injection duration proportional to engine speed this covers the fueling needs across a wide range of situations.

The reason the pump primes the system when cold is to restore the pressure so the engine can start. If the pump didn't operate while the engine was running, this pressure would soon drop resulting in no fuel being injected.

I can't remember the figures for a D-Jet so i'll give those for the later LH-Jetronic, line pressure is 43.5psi (3bar) with no vacuum/WOT/engine stopped. At idle, typical vacuum would be ~20"Hg or ~-10psi so the pressure drops to ~33psi (~2.3bar) reducing the amount of fuel injected.
As the throttle is opened, the vacuum drops causing a pressure increase on the FPR which allows the injection pressure to rise to increase the fuel for the extra air coming in. At WOT there is little or no vacuum so the pressure rises to 43.5psi to give full fueling for full load.

I'm fairly sure the D-Jet uses different figures but i can't remember them just now, i think it ranges from 30-36psi but might be wrong.

[Ron Kwas]

Alan;

Some D-Jet clarifications:

FuPu is under control of the D-Jet ECU, by way of (ECU Pin 19) and FuPuRel...but to answer the question...it runs on initial Ign ON (which charges Fuel Rail to allow Starting), but if Starting process does not immediately follow (which results in "engine running pulses" from Distrib contacts to ECU), it times out and shuts OFF FuPuRel and consequentially FuPu (this is a crash safety requirement).

Once Engine is running, FuPu is powered continuously, charging Fuel Rail, with FPReg keeping rail pressure at a constant 28-30PSI (independent of demand, with no thermal or Manifold Vacuum/Boost input or bias like in some later FI systems), dumping whatever in not being needed/used as a function of engine demand, back to the Tank, but is typically quiet enough not to be heard over engine noise...

If FuPu is noticeably loud, it can be due to a FPReg operational failure in that the Tank Return is not functioning normally (including blocked), such that the (positive displacement) FuPu is "dead-headed" or pumping into a blocked tube or system where no fuel is allowed to flow, the overpressure Bypass Valve integral to FuPu opens and bypasses the blocked path, and this results in an unusually noisy FuPu. As the FPReg normally does all the regulating and fuel circulating, this Bypass Valve is normally not functioning...its' noise typically indicates something is amiss.

Ref: http://www.sw-em.com/bosch_d-jetroni...Wiring_Diagram

Good Hunting!

[Army]

Might also be worth mentioning

On my Mercedes (much newer) KE CIS system the fuel pumps often get louder when they are grinding rust and crud from the fuel tank through their internals (!)

I assume the D-jet set up is similar where the fuel filter only protects the parts "north" of the pump - the pump has to fend for itself.

#####

@Othen

CIS - continuous injection system (in English?!) is only really a small step away from a carb. It doesn't "inject" much like many people imagine either a modern injection system or diesel injection system works...

...all CIS is really doing is supplying a kind of calibrated spray of fuel into the intake manifold.

The impressive thing with Bosch CIS is the cleverly designed conical shaped air mixing unit which uses geometric "wizardry" to balance the amount of air being drawn into the cylinders with a plunger than allows more or less fuel to the injectors.

That's all there is to it (!) - EXCEPT - for all of the additional stuff that was bolted on to get the system to behave in the real world. That's where the trouble with CIS begins and why so many people (I think wrongly) think of CIS as a total disaster...

[Laird Scooby]

Originally Posted by Army

CIS - continuous injection system (in English?!) is only really a small step away from a carb. It doesn't "inject" much like many people imagine either a modern injection system or diesel injection system works...

...all CIS is really doing is supplying a kind of calibrated spray of fuel into the intake manifold.

The impressive thing with Bosch CIS is the cleverly designed conical shaped air mixing unit which uses geometric "wizardry" to balance the amount of air being drawn into the cylinders with a plunger than allows more or less fuel to the injectors.

That's all there is to it (!) - EXCEPT - for all of the additional stuff that was bolted on to get the system to behave in the real world. That's where the trouble with CIS begins and why so many people (I think wrongly) think of CIS as a total disaster...

The CIS is most closely related to the later K-Jetronic, purely mechanical except where Lambda control is employed for emissions when an electronic interface alters the fuel pressure to correct the emissions, mainly at idle.

[142 Guy]

Originally Posted by Army

Might also be worth mentioning
I assume the D-jet set up is similar where the fuel filter only protects the parts "north" of the pump - the pump has to fend for itself.

.

Mostly correct!

The very first 1800E had the main filter located on the suction side of the pump which protected everything; but, on the 1971 142E and I think the 1971 or 1972 1800E the filter was relocated to the pump discharge. A plastic strainer / filter sock was added to the tank suction line when the filter location was changed which strained out large lumps.

The plastic filter sock invariably disintegrates with age. I always cringe when I read about people trying to fire up any D jet equipped car that has been in storage for a long period of time by adding fuel to the tank and 'giving her a try'. Sediment in the tank gets sucked into the pump contributing to the early failure of the pump motor and resulting in a rather hefty expense if they want to retain the original style pump. Draining the tank and ideally removal of the tank and flushing with mineral spirits is the correct path.

As an observation, the original Bosch D jet pumps and I think the original K jet pumps were positive displacement pumps. The rollers in the pump heads probably did not enjoy solids being included in the fuel resulting in abrasion and loss of pumping efficiency. However, I suspect that the brushes & commutator disliked solids even more with the solids contributing to accelerated wear on the soft copper commutator and graphite brushes. Modern pumps are typically turbine / centrifugal design so the mechanicals may be slightly more tolerant of abrasion; but, the commutator and brushes are probably still adverse to solids in the fuel.

[c1800]

“Really”. Alan, an attempt at humour, maybe a poor one. Not intended as criticism. There were several ads on the theme of 11 years.
Still following with interest. Keep up the good work.