1990 740 GLE motor warming-up problem (long)

[Tomca]

Hello everybody,

my Volvo 740 GLE B200E gasoline motor, Bosch K-Jetronic system has problems after start-up. I would like to find the error myself - but with minimal tinkering in the car - and for this, I will need some help to understand the warm-up controlling system of the motor.

Symptoms are the following:
- The car starts properly, after a 2-3 seconds of cranking.
- The motor starts with an increased RPM, as it is expected. The starting RPM depends on the outside temperature (as it is expected). I can see that at winter, it goes up to 1500 for a while, in summer it is only 1000.
- After about a minute, the RPM decreases down to 500. This is too small. The motor starts to shake, and that is not too good. Nowadays, during this time, I press the gas pedal to increase the RPM to about 1000, until the RPM increases back to about 800.
- This state holds about a few minutes long, until the motor warms up. It is quite annoying to regulate the motor RPM for 5 minutes long with my leg.
- I could see that the motor behaves better, if I use premium gasoline.

I would like to eliminate this problem and for this I would like to know exactly, how the warm-up regulation works. This is what I know until this:
-After start, an additional valve opens at the cylinders and injects extra amount of gasoline to make the mix rich. This valve will be open for a few seconds long, depending on the outside temperature. (I think this part works properly in my car).
- A warm-up regulator is bound on the gasoline pipe before the injector. This is a membrane-based gasoline-pressure regulator. This membrane is regulated by a bimetal that is driven by the motor microcontroller.
- An exhaust-gas recirculation system is used in the motor: part of the exhaust gas is circulated back before the air-filter via a hose. The feed-back is driven by a valve near to the exhaust pipes.

My first questions are the following:
- How does the warm-up regulator work? Does it measure the motor temperature, or simply, switches off after a minute, whatever happens? If it is temperature driven, then the problem could be here. If it is time-driven, the problem could be at the EGR.
- How can I figure out that the EGR works? If I pull down the EGR hose at the air-filter and start the motor, will I smell the exhaust gas going out from the hose? And after a while the EGR valve closes and the smell decreases?
- What do you think about injector cleaner fluids? Do they really work? And can they clean the membrane of the WUR? Can they really maintain the motor?
- And what about lead-replacement fluids? Does it worth to buy them? Is it good for the valves and pistons? Or they do not worth their price and it is better to tank premium gasoline?

Thank you all answers in advance,

Tamas

[93Regina]

1990 740 GLE B200E...Bosch K-Jetronic system

My, my....1990 K-Jet....I have no idea about specifics of your system.

In this thread, see my post (6th or so).

Cold Start Injector - Just used when engine starts, and yours appears to be working

Auxiliary air valve or idle air motor - This device is what causes an increase in engine RPM when a cold engine starts, and it appears to be working fine.

Exhaust-gas recirculation system - This system's function is to by-pass exhaust gases when engine is warmed up, and at higher throttle RPM. The purpose of by-passing gases is to cool down cylinder head temperature. When engine is not running, the EGR-valve should be closed so no exhaust gas passes thru to intake manifold. You have stated, "exhaust gas is circulated back before the air-filter via a hose," as such, this EGR system is not related to your current problem.

Warm-up regulator - Older Bosch WURs could be taken apart, and cleaned up. See my post in that other thread about testing fuel pressure. With K-Jet, system fuel pressure, etc., must be known.

Lambda-Sond Emissions Control System - I suspect yours is similar to this system.

Overview - Gasoline Fuel-Injection System K-Jetronic

Older Green Manual

O2 sensor Test

Your Vehicle - It is most likely running lean; it could be due to WUR or to Primary-pressure
regulator (page 21 in Gasoline Fuel-Injection System K-Jetronic book), but you need pressure tests to confirm. I assume your WUR has an electrical plug on it...try disconnecting it, and then do a cold start.

There are several people at another forum who know more...I could send a PM, and explain more.

Regardless, pressure tests must be done.

[93Regina]

RE: And what about lead-replacement fluids?

Your O2 sensor will foul out....not good.

Do not use these "lead-replacement" fluids...not needed.

RE: What do you think about injector cleaner fluids?

Yes, they can clean up injectors...good for CIS injectors.

[Tomca]

Thank you for your help,

I forgot to tell you, my car does not have catalyser, so I could pour even leaded fuel into it and no O2 sensor will be fouled

Exhaust-gas recirculation system: I have heard that this part has a temperature sensor, which switches off EGR, until the car warms up. If the EGR starts to work, when it should not be, it can be seen as power loss, and low RPM. Therefore I thought that this sensor also can be wrong and/or the EGR valve could be stucked.

WUR: thank you for the tip. I will try that.

Tamas

[93Regina]

car does not have catalyser

Lead substitute is only for older vehicles which do not have harden valves/seats. Harden valves/seats have been installed on USA vehicles since 1975 when unleaded fuel was introduced.

O2 Sensor - Yours did not come with one?

Exhaust-gas recirculation system - Double check, I do not think exhaust vapor goes to air cleaner, but exhaust gas goes directly into intake manifold. When exhaust goes directly into intake manifold, then vehicle can have issues when system is not functioning correctly.

All EGR system does is to reduce combustion gas temperature....if there is an issue, don't allow EGR valve to open.

[Tomca]

O2 Sensor - Yours did not come with one?
I don't know. I have two repair manuals but they don't talk about it. I know only that I can set the gasoline-air mixture manually with a little screw and a 3 mm Allen key.

EGR: your right, this valve is between the intake and outtake manifolds.

And last but not least, I found and repaired the problem! Thank you for the documentations and also for your hint about WUR plug. I think, I wouldn't find the error without them.

So, I executed the experiment your mentioned and pulled out the plug of the WUR bimetal electric heater then started the car. The result was surprising. I thought that the car will behave a bit better, since it gets more gasoline but not: the car stalled! Which means that the mixture was not lean but too rich. And the reason of it that it did not get enough air during idle. Therefore, I removed the idle air valve and cleaned it thoroughly with carb cleaner, a tooth brush, some ear sticks and even with a tooth silk. It was extremely dirty. After re-installation, the car starts without any problem.

Than you again, you made my day !

[Tomca]

One more thing: I think, I really don't have O2 sensor in my vehicle, because this was the last Volvo type in Europe, which was still able to go with leaded fuel as well.

[93Regina]

EGR:

Just repeating; if that EGR valve gets stuck open, idling and running issues will exist.

O2 Sensor

Good to hear....

Injector Cleaner - Do use it from time to time, especially if your fuel stops do not add an additive package. Since EFI vehicles, if your fueling station did not add a cleaning additive, with time, your injectors would foul up, especially on K-Jet.

I would suspect in your country there is a government mandate for resellers to use some type of injector cleaning agent. If your fuel reseller has a good cleaning additive, then there is no reason to buy a cleaning agent.

Harden Valves/Seats - It would make no sense for Volvo not to have installed them; so, there is no need to buy a lead additive.

Your Welcome!