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Old 03-01-2018, 08:36 PM   #1
bluemoose
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Default off-idle stalling/hesitation saga

So I have pretty much reached the end of the internet, and my wits, plus wasted a bunch of time and money trying to figure out the problem with my car. I'm finally giving up and creating yet another "stalling volvo" thread. The car is a 1990 740GL with Regina.

Symptom:
Issue gets worse when the car is warm. If the throttle is blipped quickly while sitting at idle, it will often stall, or hesitate and then rev up. If it is cracked open slowly the engine will rev up. In either case if the throttle is closed quickly and it falls back to idle it will try to stall or will successfully stall. Often the stalling behavior becomes dieseling behavior and the engine will run 'backwards' and blow vacuum hoses off. After it stalls it is a little hard to start again.
If the vacuum hose is pulled off the FPR idle speed will increase, but the same behavior persists when you blip the throttle. Reconnecting the vacuum hose results in idle decrease and sometimes stalling.
If I drive the car, after it gets warm, it will hesitate or seemingly start misfiring off-idle on acceleration. Once cruising it will usually run OK, but then at a stop when it falls back to idle it will try to stall. Sometimes just letting off the throttle is enough to make it stall.


What's been checked:
Everything I could think of.
-Compression was good.
-fuel pressure, inconclusive due to gimpy equipment. I have not yet tried again.
-ignition, everything is working fine as best I can tell
-timing was steady and advanced predictably at higher rpms.
-spark plugs look fine "brown toast" color.
-engine vacuum is good
-fuel relays work fine
-No OBD codes except the 3-2-1 code (supposedly caused by a dealer bulletin fix years ago?).
-IAC functions as best I can tell. It buzzes when I do the DTM test, and I cleaned it. Beyond that, hard to tell?
-All injectors fire during DTM test
-voltage steady 14.3
-TPS works fine

Parts/Money I've thrown at it:
-New battery (it died and wouldn't hold charge)
-Crank sensor (replaced as the culprit of an earlier stalling problem)
-MAP sensor
-Intake tube (had a big tear in it, but since Regina has no MAF sensor, it probably wasn't causing a problem. It was just unfiltered air, not unmetered)
-AC Delco Fuel pump, soldered into the original assembly
-Fuel filter
-short line between filter and tank hard line
- -4AN braided fuel line from filter to fuel rail (with a couple of hard to find fittings). I F'd up the original line trying to test the fuel pressure.
-spark plugs
-fairly fresh plug wires and rotor cap, but original ignition module

I've always felt like this was a fuel issue, and still do, but after replacing the entire fuel system it seems unlikely unless I did it wrong. At this point I'll take any ideas or suggestions, this has been going on several months and I haven't been able to daily drive the car for the last 3 months.

Last edited by bluemoose; 03-02-2018 at 01:53 PM..
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Old 03-02-2018, 05:10 AM   #2
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How are the valve clearances looking? My older 740 was having all kinds of weird stalling problems that I believe were likely caused by my neglect of valve clearances.

I recently did a head job on mine after a nasty overheat. Had similar issues prior where everything fuel, ignition and relay related checked out. But, it would stall at lights and turns where I had to stop.

The only thing I found when fixing up the head was that the valves had basically zero clearance. Once I got those in spec, the stalling seemed to go away and power returned.
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Old 03-02-2018, 01:49 PM   #3
bluemoose
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I have never checked the valve clearance on this car, thanks for the idea! There is no telling if the valve cover has ever been taken off this car. The dieseling behavior sometimes when it stalls led me to suspect some type of timing issue, which might make sense if the valves were out of spec. However I could just be remembering my days of trying to tune carb'd Chevy small blocks with a solid state ignition .

Last edited by bluemoose; 03-02-2018 at 02:02 PM..
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Old 03-02-2018, 03:57 PM   #4
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I just did the valve lash in my girlfriends '77 Nova. The hydraulic lifters in the small blocks are a real treat to adjust compared to the Volvo shim design. One socket and about 15 minutes of my time.
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Old 03-04-2018, 05:13 PM   #5
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So the car has now refused to crank at all. With only running it in the garage a handful of times recently, the condition has gotten worse. I pulled the fuel line, ran it into a jug, and had my wife turn it over. It squirts fuel just fine. Checked the spark at the coil and at the #1 plug, both have a spark. Pulled the spark plug after cranking, and it is wet and smells like gas, so I'm definitely getting fuel. I'm getting fuel and spark, and I'm pretty sure the air has oxygen in it , so why the hell won't it start, and why did it suddenly go from starting to not starting at all?!? Somethings stinks in Denmark and I don't think it's the cheese.
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Old 03-04-2018, 06:40 PM   #6
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Quote:
-timing was steady and advanced predictably at higher rpms.
You checked ignition timing.
How about timing belt timing?
Might have jumped a tooth or 2?
Easy enough to pop off the upper cover and check that the cam mark lines up at the same time as the harmonic balancer mark (assuming the balancer ring hasn't shifted).
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Old 03-04-2018, 09:57 PM   #7
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I checked the timing belt this afternoon, it's lined up correctly as far as I can tell. At least the timing marks line up with cylinder #1 at TDC. It has a relatively new belt and tensioner, maybe 20k miles on them. Camshaft turns with it too. I'm not sure about ignition timing. I've watched it with a timing light but I don't know that the numbers on the timing cover really tell you that much. I could see where it sat at idle, and it advanced at higher rpms, but beyond that I'm not sure about specific numbers.
I took the spark plugs out and they were all pretty wet, so I turned it over a few times with no plugs and I'm letting it sit overnight, in case it was just flooded too much to start.
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Old 03-07-2018, 01:36 PM   #8
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well, letting the cylinders 'air out' and the plugs dry seemed to solve the no-start condition, I got it fired back up and back to the original issue now.
Spent some time searching for possible vacuum leaks, to no avail. Now that I converted to AN fuel line I may look at getting an AN fitting to insert for easy fuel pressure testing, although by all other indications I am getting plenty of fuel. A vacuum leak somewhere would make more sense.
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Old 03-12-2018, 04:12 AM   #9
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If there's a lot of flooding, it would be wise to pull the dipstick & give her a good sniff. Does it smell like fuel ? If so it might be a good idea to change that oil, eh ?

Did you verify that the harmonic balancer is not slipping ?
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Old 03-12-2018, 12:36 PM   #10
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it definitely needs an oil change, it needed one before this started. One thing I had not yet considered was the O2 sensor. This weekend I did some reading and tried various tests, both in the car and on my workbench, and no matter what I could not see any voltage produced by the sensor. My understanding is that it should produce between .1-.9 volts if it is working, depending on conditions. It has an open loop between the green wire and ground no matter whether it is heated or cold, and if I'm correct that's where I should see the voltage or test resistance (the other 2 wires are for the heater?). Seems like it would have to have a closed circuit in order to get any reading there, so perhaps something is shot inside the sensor. The red and black wires have a closed circuit, but no voltage is produced there either, and I believe that is the heater circuit.

I've ordered a new NTK sensor from the parts store, and we will see if that helps.
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Old 03-13-2018, 02:39 AM   #11
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Quote:
Originally Posted by bluemoose View Post
One thing I had not yet considered was the O2 sensor. This weekend I did some reading and tried various tests, both in the car and on my workbench, and no matter what I could not see any voltage produced by the sensor. My understanding is that it should produce between .1-.9 volts if it is working, depending on conditions.
Nope. Ours (Regina systems) use Titania sensors (Wiki link), which produce a varying resistance, not voltage. Completely different than the "normal" ones used with the Bosch system.

Quote:
It has an open loop between the green wire and ground
That's the signal wire. The computer sends a voltage down the wire, and measures the resistance.

Quote:
The red and black wires have a closed circuit, but no voltage is produced there either, and I believe that is the heater circuit.
Correct, red (dark pink) is power from fuse 11, black is ground.

Quote:
I've ordered a new NTK sensor from the parts store, and we will see if that helps.
Hopefully number 25002 (Rockauto link)
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Old 03-13-2018, 02:44 AM   #12
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Originally Posted by bluemoose View Post
If the vacuum hose is pulled off the FPR idle speed will increase, but the same behavior persists when you blip the throttle. Reconnecting the vacuum hose results in idle decrease and sometimes stalling.
Was (is) there any fuel in the vacuum hose when you pulled it off? A ruptured diaphragm in the pressure regulator can let the engine suck unmetered fuel up the hose, and you might also see fuel dripping from the nipple with the hose off.
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Old 03-13-2018, 03:45 AM   #13
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Quote:
Originally Posted by bluemoose View Post
If it is cracked open slowly the engine will rev up. In either case if the throttle is closed quickly and it falls back to idle it will try to stall or will successfully stall. Often the stalling behavior becomes dieseling behavior and the engine will run 'backwards' and blow vacuum hoses off.

The o2 gives a signal(volts or resistance) to the compuker when the motor is warmed up to lean the mixture. What does a failed o2 have to do with these oddball symptoms ?
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Old 03-13-2018, 12:13 PM   #14
bluemoose
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Quote:
Hopefully number 25002 (Rockauto link)
Yep!

Quote:
Nope. Ours (Regina systems) use Titania sensors (Wiki link), which produce a varying resistance, not voltage. Completely different than the "normal" ones used with the Bosch system.
I did test resistance too, having read that some O2 sensors vary resistance instead of voltage. However, mine has "infinite" resistance since it was just an open loop between the signal wire and ground. I tried testing it on the car after running, and I took it out and tested it on the bench just using a torch to heat it up. No matter what I did, I got an open loop. Seems like something must be busted inside the sensor? Either that or I'm doing it wrong.

Quote:
Was (is) there any fuel in the vacuum hose when you pulled it off? A ruptured diaphragm in the pressure regulator can let the engine suck unmetered fuel up the hose, and you might also see fuel dripping from the nipple with the hose off.
No, no fuel or even smell of fuel coming from the hose or regulator. Also it is a new regulator.

Quote:
The o2 gives a signal(volts or resistance) to the compuker when the motor is warmed up to lean the mixture. What does a failed o2 have to do with these oddball symptoms ?
Well, my symptoms seem, at least to me, to be related to air/fuel mixture just off-idle when throttle is applied, when RPMs fall after throttle is closed back to idle, or sometimes other random times like driving up a hill. If it is assumed that the fuel and ignition system is working fine, and no vacuum leaks have been found, the O2 sensor seems like a possible cause.
I'll find out, I think my new sensor arrives today or tomorrow.
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Old 03-20-2018, 10:29 AM   #15
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I believe my saga has finally ended! Despite the old O2 sensor failing every test I tried, replacing it made absolutely no difference. I bought a $15 ignition tester and hooked it up to the Regina ignition coil. At idle the indicator light was very weak, and when I reproduced the stumbling or stalling the light would go very dim and erratic. I tested the resistance across the terminals on the coil, and was getting about 2 Ohms. It is supposed to be .5-.6 Ohm based on what I could find online.
So, I threw more parts at it. I couldn't find information on testing the Regina ignition control module, and mine was still the original Volvo/Bendix unit, so I bought both a new coil and ignition module. Installed it, hooked up the test light again, and the light was strong and steady. No stumbling when I cracked the throttle. Took it for a drive to the local ethanol-free gas station and it did well. Today I drove it the 40 miles to work and it ran fine. I still think I had more than one contributing factor even though I probably replaced some things that did not need it, but the weak ignition coil and/or control module seems to have been the main problem.
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Old 03-20-2018, 03:51 PM   #16
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Reading though your post (I haven't seen the other ones) it would be nice to have a quick summary of if and when the last time it worked normally. I have been supervising engineering troubleshooters for some years and I always ask a person why they want to replace something. 99% of the time I get the answer that, 'well, the part is in stock'. Sorry you spent lots of money replacing good parts. Some of your tests all made sense to do, but you did not do sufficient work to get a yes/no answer. For example, your ignition test should have been done on an analyzer (or scope if you have one). A shop analyzer would also pick up worn out spark wires...another common source of problems.

Now that you found the problem, it won't be of interest that many of the older Regina ignition modules fade away like yours did. The only reason I can think of for that type of failure mode is that racing the engine heated up either the coil windings, or the switch transistor in the primary and caused a momentary failure until it cooled back down.

These cars really respond a multi-spark ignition if you can re-arrange a few parts under the hood. The ignition trigger signal needs to be inverted to be used with standard MSD and other like products. A hotter and more reliable coil is required. Just FYI.

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Old 03-20-2018, 06:43 PM   #17
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Reading though your post (I haven't seen the other ones) it would be nice to have a quick summary of if and when the last time it worked normally.
I do think some of my failure to diagnose this quickly was a lack of good diagnostic tools, and a lot of difficulty trying to find information about Regina. There is tons of very detailed troubleshooting and specification info out there for the Bosch systems, but relatively little for Regina. Also I had to weight the cost and time of trying to set up proper diagnostic tests and obtaining the right tools, vs. just buying relatively cheap parts.

I'll try to summarize the troubleshooting process when I get a little time later.
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