This is a new chapter in the hair-tearing-out saga here: https://www.brickboard.com/RWD/volvo/1594228/740/760/780/powerloss_heater_core_replacement_pulling_hair_power_loss.html

1990 740 with a 1992 -560 ECU turbo and w/egr

Sooooo... After replacing my heater core, I've found my car drops injector pulses, and I lose engine rpms as a result. The problem is pronounced when warm and between 1300 and 3200-3500rpm. Outside of those ranges, there is no noticeable problem.
I figured out that I'm losing injector pulses by backprobing an LED into an injector while the engine was acting up. I had an inline spark tester, and the spark was flawless.

So, my logic is that is must be either the ECU, ICU, Wiring between them, or a fault between the ECU and injectors (maybe the RSR wiring, but I just replaced the RSR and the wiring pigtail to it).

So. I've got the greenbooks, but I am getting confused on what pins on what control unit should be hot. I've tried 3 pairs and all of them show 0V, but if that were true, the car wouldn't be running. I must have the wrong pins.


Here are my burning questions:
What pins is the signal from the ICU to the ECU on?
What does the signal look like? Is it a steady voltage or is it pulsed?
What is the "signal generator" referenced in the ignition greenbook? (The 700 ignition book starting on page 61 in the pdf and 59 on the text says ICU pin 17 sends a signal to ECU pin 1, but gives no description of the signal.)

I'm getting close to figuring this out... I think.
Cheers

FIXED!!!

https://www.brickboard.com/RWD/index.htm?id=1602774&show_all=1

Sooooo after looking at the wiring diagrams and seeing that pretty much every affected system relies on the main/fuel relay, I pulled the "known good" main relay and was planning to make it into a bypass test relay, and then looked at it.....

Cracked solder leads! Lots of them. I don't know if this is the problem, but maybe it is. They relay wasn't clicking while I was driving, but that doesn't mean power was getting through all the pins.

So, once I get a new (used) turbo installed, we'll see if that was it.

Hello Will,

Does your car have ODB? I think 1990 cars onwards have this for turbo and non-turbo version. I may be wrong though.

Amarin.

1990 740 with a 1992 -560 ECU turbo and w/egr

Will; I am positive that a 92T did Not have a 560 ecu. My 92T/egr had a 939.
Also, is it a pink label? These are famous for problems/failures.

My 92T had greentops, with a ballast resistor. If you put in resistor type injectors without a resistor, the ecu may be blown. There is a current thread on exactly this issue on TB.

Hrm. I'm beginning to wonder about it being from a 92. I guess I should forget the year and go with the -560 designation with a red label. The -561 I know had both white and pink label versions. It's been running without problems for about 14 years, so I don't think the injectors are to blame, but I'll check their resistance and color. They might be greentops, I don't really remember. Are those resistor types?

I found a wiring diagram at And it shows the main/fuel pump relay being energized through pin 20 and then going on to power the injectors, the IAC valve, the AMM, and pins 9 and 21 on the ECU. I'm not sure what those do, but so far, I've had false codes thrown for a bad AMM, a code thrown for too-rich/lean at idle while cruising down the highway, and I'm losing injector pulses. As far as I can tell, the IAC is working fine.

Next to check:
Injector/ballast resistor supply power when running and losing injector pulses.
Main (fuel pump) Relay, pins, and wires into the back of the relay tray are secure and fiddling with them doesn't cause problems.

ECU ground again for the heck of it.
ECU ground pin to body has 0 ohms resistance.
That ECU pin 20 has power at all times while engine is running.
AMM pin (not sure which one) has power during missing pulses.
That pin 18 has power and that the wire feeding pin 18 has power in the engine bay.

560 pink/red label is the single most cited one for problems.

I thought it was only the 561 pink label. I had no idea the 560 or red label were suspect.

Most of the colored non turbo ECU's had the problem but I do not know if it was an issue with turbo ECU's? If you have a LH 2.4 maybe you should look for a LH 2.4 940 turbo ECU.

Dan

Hello Will,

Ok...I've re-read your previous post and you've had false codes before. Sorry.

The turbo injectors should be the green tops. They are peak and hold type hence the need of ballast resistor pack to prevent ECU damage.

Regards,
Amarin.

Well... I'm not sure the codes are truly false. There might be something else causing the main relay (runs fuel pumps) to shut off and that feeds both the AMM and TPS. The ECU might be seeing bad signals from them as a result. Maybe I should buy a brand-new relay for it.

Though, my diagnosis is on-hold right now.... my turbo's blown bearings turned into blown oil seal, and it's not a good idea to run it.

I've never tracked down this kind of problem, but I have read the ignition part of the green book. Do you have that one? It explains the theory behind the EZK and all the sensors (maybe that's what you and lucid are referring to).

I've got the greenbooks for 740s on DVD (adequate but wish I had paper version).
Anyway, there is a page showing what circuits are activated when the key is position I, II, and III, its one of the general wiring books. This could be useful to see what circuits are hot during ignition.

If my memory is good, the Injector circuit is out of ECU, So maybe track backwards:
All the injectors fire at once but there could be a problem with that circuit going from injectors to ECU. Then check circuits from ECU to ICU that control injectors.

In the back of my mind, I wonder if it could be an ignition problem, not an injector problem, because I think the computer calculates ignition before fuel. Fuel is just constant pressure and on-off signals to injectors, about as simple as it gets.


--
I own a Volvo or Does Volvo Own Me? Try the easy to search Expanded Style FAQ Index http://40mph.com/Brickboard_700-900_FAQ_Expanded_Index_Version/

I'm sure it could be a problem with the ignition computer, but the spark never even hesitated at all during my tests.


I checked the RSR today, and all 4 pins had steady power to ground during the episodes. I think it's down to the ECU, ICU, or wire between them. Hopefully.
I'll look over the greenbooks and wiring diagrams again to see what exactly triggers the injectors.

Just a guess. Do you have a ballast resistor in your setup?
--
Post Back. That's whats makes this forum work.

Hmmm. Yes. Yes, I do. And they're a lot cheaper than a used ECU.

I verified that the ECU is getting a constant 7.0-7.5V signal from the ICM. I tested the "signal generator" by probing pins 10 and 23 on the ICU. It says the resistance range should be 215-265ohms. Mine measured about 180ohms with the connector attached. That's out of spec, but I didn't see any variance in the voltage to the ECU pin 1 (measured at ECU-1) nor any dropouts - neither with the Digital nor cheapo analog meter.


So, I'll check that the ballast resistors are still getting power and the injectors are still getting power. Hmmm. So long as the injectors have power, that means the ballast resistors are working.

If the injectors have constant power and they're just not being grounded, I'm going to blame the ECU. I've never heard of another ECU failure like this though, other than seemingly random error codes.

Hi Will, aka Car Surgeon, as in Weird Al's spoof...

In Big Harry's thread on the 200 forum you asked me to put my two cents in on this. I try to stay out of stuff I don't know, and as much as some think 700s are like 240s, I will step ignorant into the differences every time.

For instance, the question about the ballast... I thought only turbos had those injector resistors. Well yours may indeed be a turbo. Just an example where I can't offer real experience. My turbos are k-jet 240s -- the ignition is ballasted, not the fuel injectors. :)

But what Amarin suggested is exactly what I think about this "missing injector pulse" red herring. Not that red herrings are not valid learning experiences, but lets consider putting the horse on the other side of the cause-and-effect cart: Your noid light quits because the car is in rapid decel. And, if you were to measure vacuum at the same time, I bet you'd see it drop too as the IAC tries to keep decel vacuum from sucking all the oil past the valve guides.

When I watch your video, or more importantly, listen to it, I think the fuel computer sees airflow cut off. I wonder why: Does it see a suddenly dropping AMM voltage, or does it see TPS closing. Try monitoring AMM voltage at the fuel ecu, which you can actually do with a multimeter. Check what happens at your noid light if you ground the TPS closed throttle contact while you have it running a couple thou rpm (throttle obviously open). Again, convenient at the fuel ecu plug.

Anyhow I have put a scope to 16 and 17 on EZ116K ICM outputs before -- 16, the one that drives the spark includes the dwell (width) information, and 17 is simply spark timing, which is enough to give the fuel computer what it needs to know about engine speed. I believe you won't see it disappear in sync with your noid light going black. It is 8 which tells the ICU what it needs to know about ignition advance from what the ECU learns from your AMM about engine load.

None of this is going to be conclusive to you without being able to see the timing and waveform. Maybe if your multimeter has a duty cycle function along with its frequency scale, and you get some experience from a correctly working system. That's what I was shooting for about 8 years ago, testing a few ICUs and ECUs in Mrs. B's 245 -- a baseline. I was following the oft heard advice to keep spares, especially AMMs and ECUs. Much cheaper at the junkyard before you really need one fast.


--
Art Benstein near Baltimore

First Guy (proudly): 'My wife's an angel!' Second Guy: 'You're lucky, mine's still alive.'

Hey, Art. Thanks for stopping by! I really appreciate it, and your level-headed meticulous thinking is something I don't entirely have nailed down. Plus, I'm not that familiar with the ECU. Most problems are things people have encountered before. This one seems like a real nut to crack.

I think that checking things at the ECU is the way to go - that verifies entire circuits at once. On that note - is it Pin 8 on the ECU that is the input voltage from the AMM? I see there are 3 pins into the ECU from the AMM.
Is "It is 8 which tells the ICU what it needs to know about ignition advance from what the ECU learns from your AMM about engine load." referring to pin 8 on the ECU?

And yes, I ran across ballast resistors in different systems trying to search RWD for ballast resistors. The vacuum does drop off, though the throttle plate is still open the same amount. I can see if I can feel the IAC move/click when it cuts out.

So many things to verify, but at least it's a finite list now!

Hello Will,

Since you have a voltmeter why not measure the resistance of each injector first before blaming the ECU. And compare the reading to those in the greenbook. They should be the same all of them. I'm guessing here that one or more injectors may be faulty rather than ECU issues and ECU is cutting power to save itself.

Also check that the injector connections are secured. There's a small square rubber seal within each injector electrical plug. Without this seal the connection may vibrate.

Just a suggestion,
Amarin.

Amarain's idea to check the injectors is good. In the original diagnosis, they were back probed so either the wiring or injector could be causing a problem. Ruling out worn injectors is a good idea, and worn injector connectors.
--
I own a Volvo or Does Volvo Own Me? Try the easy to search Expanded Style FAQ Index http://40mph.com/Brickboard_700-900_FAQ_Expanded_Index_Version/

Here are my burning questions:

1-What pins is the signal from the ICU to the ECU on?
• ICU 17 to ECU 1

2-What does the signal look like? Is it a steady voltage or is it pulsed?
• Pulsed, derived (I believe) from CPS pulses to ICU 10 and 23

3-What is the "signal generator" referenced in the ignition greenbook?
• Probably special test equipment to simulate the "signal" referred to here ==>(The 700 ignition book starting on page 61 in the pdf and 59 on the text says ICU pin 17 sends a signal to ECU pin 1, but gives no description of the signal.)

That's about as deep as I go.


--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Looking at this again, and at the greenbook, I get the impression there's a signal generator inside the EZK unit that can be tested. It says "test between pins x and y..." and gives a spec of 225-260 ohms for it.

Be that as it may, that's exactly what I needed to know.

I tried probing ICU 17 to ECU 1 last night, but saw no voltage, amperage, or anything at all on my cheap little analog meter. I'll try it with my more expensive DM and try running it on the Hz setting. That picked up the CPS feed directly.

Thank you!

The only 700's I ever owned were both Regina, but it seems that folks that had Bosch's with ignition power stage grounding issues said it got worse when warm and the corrosion-induced resistance between the power stage and the chassis increased. Have you tried pulling it loose and cleaning the mating surfaces?

Removed, replaced with a good used one, applied new thermal paste to the heatsink surface.