Cold start problem

1970 Volvo P1800E.  Cold start system does not use a thermo-time switch but rather a thermo-relay in the ECU which grounds the cold start relay. Relay test good and power present while cranking to relay.  Coolant temp. reading verified at ECU and accurate.  ECU is not grounding the cold start relay.  

Has anyone seen this?  Common?  Internal ECU fault with thermo-relay?

Thanks
 

Hi Unknown,

please have a look at our Netiquette .

Depending on version of your ECU it has this electronic thermo time switch or not. So what is your ECU no?

Hello,
Apologies for my blunt entry. My name is Kurt and I am an owner/operator of a Volvo specialty shop in Santa Fe, New Mexico, USA. I have enjoyed this forum and its well of information in helping with various shop work.

My ECU has a sticker that shows it to be a remanufactured unit by Bosch Volvo of America Corp with the following numbers on it:

5-243315
0280 000 034 094
224705

I am referencing the Robert Bosch D-Jetronic workshop manual for Volvo.

Hi Kurt,

that is what I feared. If you look at my chapter 3.9 of ECUs you will notice that there are various ECUs for Volvo. Column "Coldst" shows that your ECU 0 280 000 034 is without electronic thermo time switch. It is for cars with external thermotime switch. You need 0 280 000 017 or 009 with 0 280 100 010 MAP sensor. Or you install a VDO thermotime switch and ensure 0 280 100 035 MAP sensor.

Hi Curt,
the 0 280 000 34 ECU is a newer type without the cold-start-function and without the shut-off at decelleration.
It doesn't fit the car...
Look a the ECU - section of Volker's compendium and you will find the unit that fits the car.

Regards
Norbert

edit: Volker is faster than me...

Hi Norbert and Kurt,

correct 0 280 000 034 does not have overrun-shutoff. But that does not matter a lot - only in fuel consumption. But missing electronic cold start feature lets the car start badly when cold. And combination with MAP sensor must also fit.

Wow! This is very interesting.

What would be my option to get the cold start to work without changing the ECU? Adding a thermo-time switch? Or adding a momentary grounding switch that the driver can push while cranking?

I wonder if this also would account for another problem that I have had with this car.

About a year ago, I tried to convert this car to the 123 electronic distributor without success. After much testing of two different 123 distributors, my findings found that the switching signal is opposite of what the 123 distributor creates. I don't remember which way it was, but the 123 distributor would not trigger the injectors. The original points distributor works fine and is still installed because of this.

Thanks all for this help.

Kurt

As a side note, the current MAP installed is 0 280 100 010.

Any help or ideas locating the correct ECU for my application would also be appreciated. I would like to give my client the option of getting this put together with the correct parts.

Thanks,
Kurt

Hi Kurt,

easiest way is to install 0 280 000 017 ECU. I will check whether I have one. I am not sure. Otherwise you have to modify wiring harness, install VDO thermo time switch and find a 035 MAP sensor. And you loose over-run shutoff. I think I once compared 017 and 034 ECU and found that they are very similiar.

And just forget 123 ignition. Use Pertronix / FullMax / Powerspark to replace ignition contact with a transistor. That is best solution. 123 has a very interesting way of double firing trigger contacts (on Volvo - thats where i measured it). I have contacted them for an explanation but I could never get one.

Hi Kurt,
the 0 280 000 017 is available in the U.S.A. This would be the easiest way... the ...009 seems to be available only in Australia <high-priced>.
www.ebay.de/itm/234206710490?hash=item36...a:g:QM4AAOSwZm5hQPna

Regards
Norbert

Hi,

I would not recommend 009, it has no idle-run rheostat.

Thanks for the help and advise. Let me know if you can source the correct ECU for my application. I will be looking into some of my more local sources as well as the web.

Kurt

Hi Kurt,

Norbert has linked to the correct ECU. Just buy that one. If I find my Volvo ECUs (which I have not on first sight), it will be too costly with shipping and currency exchange. So I will only search again if I find my ECU.

Hello,

I have sourced several correct ECU # 0 280 000 017. One from Ebay and one from a local source.

Any advise on what to look for or what should be tested to be sure the replacement ECU is in good working order. Is there a way to test the internal MAP sensor?

It appears the Bosch Classic repair service is not available for the North America market. This is from the Bosch Electronic Service website:

Dear customers,

due to the “Brexit” we are only able to process orders and new registrations from customers from UK and Northern Ireland if you enter a valid EORI number.
The EORI number (only valid for GB) will start with ‘GB’ followed by 12 numbers, for example GB123456789012.

If you have any questions, please contact our customer hotline (tel: +49 (0)5121 49 5720)

Your Bosch Electronic Service Team

Thanks,
Kurt

Hi Kurt,

well just install and test it. Normally a Bosch Service should locally hande your service request and forward to Bosch Classic in Germany. That should work. But yes Brexit has unnecessarily complicated life. Even if I wanted I ould not be able to offer help as I would not be able to import and export an ECU with all customs formalities. So I undestand those difficulties.

On MAP sensor you can do resistance, ground and vacuum leakage test. If it is from 70s (date stamp on rivet upper right or on housing back) x2x or x3x it should be trustable. But of course the devil lies in the details.

I now have a correct ECU and the cold-start problem is mostly resolved.

At temperatures above 4 degrees Celsius (40 degrees Fahrenheit) the engine will crank and run and warm up normally. Below this, it will crank, run, and then stall. After 2-3 more key cycles it will stay running but rough and then begin to smooth and run.

During the colder starts, and once it does stay running, the idle will now surge until it gets a bit warmer. This is a new condition with this ECU. Before, the cold idle was always high until the engine warmed up and then the idle would drop to normal. A bit erratic, but functional.

I think I have a faulty Auxiliary Air Valve and now with the correct ECU installed, I am seeing the over-run function working. Does that sound like a correct assumption?

Did the re-manufactured ECU that was installed have the over-run function? Please reference the beginning post for that ECU number.

What are my options for the Auxiliary Air Valve if it is needed?

Thanks again,
Kurt

Hi Kurt,

its all in my compendium

List of ECUs also contains their features.

Thanks. Found it and also realized this information was given earlier in this thread.