Volvo 164 73' horrendous fuel economy!

Hello i am new to the forum and have a Volvo 164 '73 b30e djet from Australia. The engine is freshly rebuilt with a slight port and mild camshaft (K). it has 8000km post rebuild and has been running well aside from horrendous fuel economy upwards of 21L/100km.

I have followed the trouble shooting steps on this website and unfortunately still have been unable to trace the problem. i have verified the temp sensors appear to show the correct ohms. i have only tested within one temperature range at the ECU and it appears to match the ohms at the sensor. MAP sensor presents the correct ohms and using a vacuum pump it just comes within spec of the vacuum leak test (this however is right on the line).

I have installed a wide-band sensor in the exhaust and this sensor tells me that the AFR mixture is 14/1 or about after the cold start valve shuts off and it progressively gets richer as it warms up aprox 12/1 at idle and cruising. logic would dictate that this is the opposite of what should happen. this is also set with the CO idle screw turned fully to the left.

i have posted in the intro and Thankyou to Volker for welcoming me. To answer your question Volker, yes the sensors to appear to be reading the correct values at both i have not tested the at the wiring connector at various values just after the car has been sitting so i will need to test once warmed up to confirm wiring is not the issue.

i also have a significant warm start issue which i have overcome by adjusting the fuel pressure above spec to 34-38 psi

Cheers

Hi Al,

well warm start problems normally occur if either injectors, restrain valve on fuel pump or fuel pressure regulator are leaking. How quickly is fuel pressure dropping after you switch off ignition? You should not try to compensate by increased fuel pressure as this increases fuel consumption in all operating conditions.

When I look at your MAP sensor, it has rivets and potting on this picture looks original. Did you verify that it is the correct Bosch no. fitting also to your ECU and engine? You have compatibility tables in my compendium in chapter 3 and 4. On the other hand 10s leakage is on the border of a failing unit. It means that your diaphragm has started to tear. The trouble is that it is hard to say how far. In the beginning it opens just a little, especially in idle-run. This tear increases day by day and it is hard to say how far it will open during operation.. So if there is nothing else you can find, I would recommend getting it repaired by Bosch in your country.

I have checked and it appears the fuel pump will retain pressure for at least 15 minutes if not longer. with the b30 its a non cross flow head and i wrapped the manifolds which i believe may be holding more heat in and causing vapour lock issue.

yes i have verified it is the correct number for the car i have also swapped another ecu in as a tester and verified they both are designed for the vehicle and it changed nothing.

yes i may try source a known working MAP sensor however it seems to work although the mixture does tend to lean out at the top rpms possibly due to the extra air flow from the camshaft.

i am perplexed as to how a faulty map sensor would cause the mixture to get richer the engine warms (unless as the sensor warms the diaphragm leak gets more noticeable). i will test the resistance at operating temperature at the ecu terminals to see if it reads correctly.

to have the MAP fixed by bosch i can imagine id be better off fitting a new engine management system haha

Hi Al,

well it seems your injextors and retain valve are then okay. But then warm start should not be a problem. MAP sensor will NOT VARY its resistance by temperature. And resistance is not important . It is a linear transormer that varies voltage peaks from ECU depending on vacuum applied.

But what does

Al wrote: yes i may try source a known working MAP sensor however it seems to work although the mixture does tend to lean out at the top rpms possibly due to the extra air flow from the camshaft.

mean? Did you change bore or manifold?

Hi Al,
are you sure the speedometer counts the distances in the metric system?

As far I know, Australia changed from imperial to metric system in the seventies.
Is this a RHD car?
Maybe this export car (Commonwealth) was equipped with an imperial speedometer...

Just an idea

Regards
Norbert

Hello Al,

do you know this VOLVO Service Manual?

2 (24) Trouble shooting
Fuel injection engines
TP 10812/1

Chapter 6 - Excessive fuel consumption

Kind regards

Jörg