85' 760 endless starting nightmares

Wilfy

hey all, I've recently fixed the fueling system on my 85 760 (B28 something) and its not wanting to start.

for some background. I have done the tank pump, fuel relay, and had to fix a heater core hose leaking. That last part required me (maybe it didn't but it made it easier) to take off the fuel distributor. The previous owner has put a new distributor, coil, plugs and wires.

After doing all this, it appears to be flooding. I get fuel to the distributor, and on pushing the sensor plate, I hear injectors. With all this working, it doesn't start. I blew out any fuel from the system by taking the relay out, where it ran for probably 10 seconds, before it died again.

My thoughts are either the auxiliary air valve, cold start injector, or leaking injector. I can't say I know much about these engines, but the consensus from the redblocks leads to that.

I'm aware this engine is poop generally speaking, but I don't have the shop to do anything fun like an engine swap (not even a good tree to block and tackle it out with)

any info would be appreciated.

Ex850R

Even a good Volvo spanner twirler can have problems diagnosing some of the vagaries of K-Jet and the V6 (D-Jet?)so find a good whisperer and hand it over as parts throwing isnt a good thing.

Wilfy

Ex850R I'd argue I'm not throwing parts at it, hence the reason I'm asking here instead of just pulling shit off and finding out on that way. If you know anyone local to Victoria who has time to look at it, it would be appreciated. I haven't found anyone nearby that knows the K-Jet system but I'm sure people know people.

jamesinc

The aux air valve won't be your issue. If the car runs with some pedal but won't idle, then maybe it's something to think about. But not running at all? Won't be your aux air valve.

Leaky cold start injector, or leaky injectors generally, is the right place to start. It is relatively easy to diagnose, you pull the injectors and put them in bottles. 390ml coke bottles are a good size. Then you lift the air flap with the motor off, system springs to life, and you can check the fan pattern and opening and closing of the injectors. You want to see a nice even fan from very low airflow all the way up to max airflow.

It's also I think possible to reverse the wiring between the aux air valve and the cold start injector, so you should also attach 12V test lamps across the Aux valve plug and the cold start plug. You are wanting to see the aux valve powered at all times. You want to see the cold start valve illuminate for a few seconds at most when you first switch the car on, then go out and stay out.

If you are wanting a very convenient tool for testing the wiring connectors in KJet, I recommend one of these: https://www.australianonlinecarparts.com.au/gm-pfi-bosch-2-noid-light

Ruling out electrical issues and injector issues, you'd next want to get a KJet fuel pressure tester and check your pressures (control, system, rest).

If your system pressure is off, you have a fuel delivery issue. If your control pressure is off, you have a problem with the control pressure regulator a.k.a. warm-up regulator. If your fuel pressure needle doesn't sit still but vibrates constantly, that's a faulty fuel accumulator, the vibration is the pulsing of the fuel pump (it can cause really bad running if the pressures aren't stable).

If your pressures are correct, you maybe have a mixture issue but KJet has a good reputation for holding its calibrated mixture even after 40+ years of use, so that's not super likely. You'd need a CO tester to tune it anyway, it is very sensitive.

Otherwise it would have to be a motor timing or ignition timing or some other ignition issue.

Wilfy

jamesinc Thanks for the info, I'll get to checking asap

jamesinc

No worries, and if you want the Volvo specs and diagnostic procedures they are on https://ozvolvo.org/archive just search for "fuel", all the CI fuel system manuals are for K-Jet.

dano

It sounds like you've got a K-jet system. One of the critical parts for starting in a K-jet setup is the warm-up regulator. It adjust the control pressure in the fuel distributor so that it increases fuel delivery when the engine is cold. Low pressure = more fuel, high pressure = less fuel. If the pressure is wrong, then you will get too much fuel and the engine won't start, which sounds like what you're experiencing. In order to diagnose your setup, you need a fuel gauge with the correct fittings. This is the kit I used on my saab: https://www.ebay.com.au/itm/314345140806

You can also make your own noid light from an LED and a 600 ohm resistor. With a bit of heatshrink you can make it so that it plugs directly into the junior timer socket.

Image description

Wilfy

dano aha, sketchy and simple, love it.

I'm definitely going to test the pressures soon, I've just found some more dire issues that I'll get too first. thanks for the link to the pressure gauge set.

Wilfy

Quick update for anyone that's curious.

Couple of days ago now I got some extra free time, so I checked the injectors. All of them, including the cold start, work just fine, no leaks, good spray, etc. Using an ancient test light to the cold start injector and aux air valve resulted in whats expected too. With the last of the time I had I decided to check the spark. it's never given me any issues, and I had no concerns, but why not.

No spark.

did some further digging today. No power at the coil. No power anywhere in the ignition. Smelled like a birthday party though, or that time my stove caught fire.

the ignition ECU (?) had caught fire. specifically a pair of aluminum flat wires melted. I'm not 1000% sure of the name of this part, however I searched the part number (0 227 100 007) and that was what sellers were calling it.

The plan at the moment is to fab up some replacement wires and solder them in. I don't want to put down the seeming 400 dollars for an engine I'm not particularly in love with, however I'm confident in my ability to fabricate and solder these parts in.

before I do though, does anyone have any experience with these blowing like this? I'm guessing these wires blowing comes from either a voltage surge or a broken resistor, but I can't identify any areas where that has happened.

Also, if anyone has one sitting on their shelf, I'd be happy to relieve you of it, just not for the asking price of the car 😆

Major Ledfoot

0 227 100 007.... Pretty sure it was @1971_144GL who had a module with that part number floating around somewhere? It was a while ago, and we were looking at various ignition modules' part numbers trying to work out what they're from, and if they'd fit a K-Jet 240. Do you know if the coil is original? IIRC these ignition units are quite 'coil sensitive' meaning aftermarket ones won't gain you anything (the opposite in fact).

Wilfy

Major Ledfoot coil seems original as far as I remember. I'll have to check for a date/model on it tomorrow. Tbh I should have seen electrical like this coming seeing it had a lawnmower battery in it when I bought it. 500 dollar car things.

jamesinc

I'm pretty sure the B28 version of the ignition module is hard to come by. The 4-cyl version is plentiful, and tbh I don't even know why the 6-cyl one would be different, unless the signal from the distributor is different somehow, but from what I've heard it can be a hassle dealing with the B28 ignition modules.

Wilfy

jamesinc Do we have electrical diagrams of the 4 cyl? I could totally compare them and try to find out

dmc

Pretty sure I had one of them and gave it a way a few weeks back. Try @DCW242 as he has the box of K-jet bits I gave away and also has a few of these engines.

jamesinc

The only thing I could think of is that the number of cylinders might affect the circuitry that governs dwell time.

From ozvolvo.org/archive:

Image description

The circuits look the same externally. Someone on Turbobricks years ago fully reverse-engineered the ignition module's internal circuitry, there's a hand-drawn schematic somewhere but I have so far been unable to find it.