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Old 08-30-2019, 06:46 AM   #26
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Here ya go: https://greenbook-archive.s3-ap-sout...3a5daba875006b



Courtesy of https://ozvolvo.org/archive/

Also, you can measure the resistance on the MAF itself to make sure it's in good working order.

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Old 08-30-2019, 07:08 AM   #27
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Something about that green book troubleshooting drawing doesn't sit right. The wire color codes look to me like pubs grabbed them from a 7-series maybe. The interior drawings in the green books are rife with this sort of error. This one manages to have the correct wire colors and pin numbers for a 91 240:



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Old 08-30-2019, 11:09 AM   #28
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Armed with the wiring diagram, how does one diagnose the MAF circuit??
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Old 08-30-2019, 02:06 PM   #29
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Saved the ozvolvo website. Takes some getting used to the organization of stuff on there. Thank you Art and Ogamer. Checked the resistance across pins 2 and 3 on the MAF to measure 3.6 Ohms (within spec)
Checked voltage at pin 5 of the MAF wire harness with respect to ground -> 12.1V
Checked the voltage between pins 1 and 5 on the MAF wire harness -> 12.1V

Seems like the MAF checks out? What can I check next? Could a bad ECT be causing this?

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Old 08-30-2019, 03:20 PM   #30
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Default AMM Troubleshooting -- Have a Known-Good Spare

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Armed with the wiring diagram, how does one diagnose the MAF circuit??
About all you can do with a multimeter is check for some very basic faults in the wiring, and some not very common faults in the AMM itself. I prefer calling the Bosch hot wire air mass meters AMMs and leave the GM terminology "Mass Air Flow" sensors to the later film-based units. The resistance check is a lame attempt by Volvo's early tech writers to check for a broken wire. In actuality, there's a temperature-dependent resistor across those terminals which ordinarily reads within the specification given for both together, so, unless you're using rather sophisticated resistance measuring equipment, the "ohm check" is useless. Just look at the wire.

Most LH2.4 air mass meters fail just out of range of the adaptive capability of the ECU, when they fail, whether from overcooked electronics (the airbox tstat culprit) or from heavily contaminated platinum. My opinion is that a certain number of Air Mass Meters are put in their graves by enthusiasts wielding cans of "Mass Air Flow Sensor Cleaner" or so it seems reading the stories here and elsewhere.

So what can you do with a wiring diagram and a multimeter? You can prove one either suspect or bad, but you can't prove one good.

Check the output voltage at rest -- that's the white/red wire. Turn the ignition key to KP-II without starting the motor. Slip the boot back and probe the rear of the connector. Measure the voltage from the negative battery post to the white/red wire. While doing so, also check to be sure the black/brown wire has a good connection to ground as evidenced by less than 200mV on the plug pin. And like the OP did, make sure the battery power is good at the orange wire (1991) or red/black (92-93).

I like to see the output of the AMM at white/red above 1.400V, with no air movement. Yes, I've seen them working well even down into the high 1.290's, but with some ECUs and not others. This is hairy edge territory in my opinion. Make sure the hot wire responds by tweaking the corrugated hose a tad to see the meter fluctuate upward. No need to disassemble the plumbing.

You can start the car and see how the output responds to the throttle and where it is during idle, but the airflow/temp conditions vary so much, there's no number you can assign that will discriminate between a good and bad unit in all cars. The response is non-linear.

But bottom line, the only definitive proof, without a temperature controlled flow bench, is to substitute a known-good unit. My advice for 20 years has been to acquire at least one good spare before it is needed and keep it on hand for troubleshooting. Junkyard AMM with a day spent in your car is good insurance.

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Old 08-30-2019, 09:11 PM   #31
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^ I appreciate the very detailed write up.
The AMM in the car now is a replacement used Bosch unit that I got from a member over here.
The symptoms are the same whether it’s the original AMM or the replacement one (both are Bosch016 and not aftermarket).

I can try the output voltage test that you mention above next week.
Out of curiosity, could a faulty/malfunctioning ECT be causing the troubles?

Again, appreciate everyone’s insight into this so far.
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Old 08-31-2019, 03:25 AM   #32
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Quote:
Originally Posted by 240-FAN View Post
^ I appreciate the very detailed write up.
The AMM in the car now is a replacement used Bosch unit that I got from a member over here.
The symptoms are the same whether it’s the original AMM or the replacement one (both are Bosch016 and not aftermarket).

I can try the output voltage test that you mention above next week.
Out of curiosity, could a faulty/malfunctioning ECT be causing the troubles?

Again, appreciate everyone’s insight into this so far.
It is possible both units are defective. It's uncommon, but not unheard of. If it was shipped, it is possible it was damaged during transport. They are kinda delicate.
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Old 09-04-2019, 09:56 AM   #33
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I checked the resistance across both units as well as did a visual inspection. The "filaments" inside both of them are intact.
The fact that it struggles to start and idle smoothly on really hot days has me suspecting the ECT. I should be able to conduct the output test Art outlined above hopefully tomorrow or the day after.
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Old 09-05-2019, 10:24 PM   #34
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Ok so did some checks. Here are the numbers measured at the ECU:

Injectors - pins 9 and 18 is 4.4ohms
Idle valve - pins 9 and 33 is 8.2 ohms
Cold start valve - pins 9 and 32 is 11 ohms
AC compressor - pin 14 and ground - 4 ohms
Voltage at red/white wire on AMM with key in KPII - 1.53V

Interestingly, I can’t get any reading on pin 13/ECT at the ECU. It just shows the default “1. “ on the DMM. What does that even mean?
I would think a bad ECT would still read a value out of range?

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Old 09-05-2019, 10:42 PM   #35
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That means the reading is out of the range of the setting you have it on.

Do you have a good MAF reading, backprobed at the ECU?
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Old 09-05-2019, 10:47 PM   #36
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Not sure if I ever measured it at the ECU.
I’ll take a look at it tomorrow - pin 5 and ground correct?

Anything else I can check with the ECT?
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Old 09-06-2019, 06:16 PM   #37
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So I went back and measured the resistance across pins 6 and 7 on the ECU -> 3.6Ohms (within spec)
ECT at the ECU pin measured 2321Ohms on a cold engine. With the block measured at 86C, I measured resistance of 276Ohms (DMM registers 0.276 with the dial set to "2k") So what gives?

Edit: the past 3 times I have driven the car, when I start her, she shakes and stumbles for a few minutes before settle down. Also, when I give her gas to merge onto the street the first time, she will bog down for a few seconds and then catch up. Not quite sure if that points to anything at all?

Last edited by 240-FAN; 09-07-2019 at 07:47 AM.. Reason: Vehicle behavior added
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Old 09-07-2019, 03:09 PM   #38
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Quote:
Originally Posted by 240-FAN View Post
So I went back and measured the resistance across pins 6 and 7 on the ECU -> 3.6Ohms (within spec)
ECT at the ECU pin measured 2321Ohms on a cold engine. With the block measured at 86C, I measured resistance of 276Ohms (DMM registers 0.276 with the dial set to "2k") So what gives?

Edit: the past 3 times I have driven the car, when I start her, she shakes and stumbles for a few minutes before settle down. Also, when I give her gas to merge onto the street the first time, she will bog down for a few seconds and then catch up. Not quite sure if that points to anything at all?
Sounds like an air leak of some sort. Are you able to measure AFRs? Or exhaust temp?
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Old 09-07-2019, 06:43 PM   #39
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Is there a simple way to measure/DIY to get the AFRs? Also, for exhaust temp, is it just using a hand held thermometer and pointing at the tail pipe?
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Old 09-07-2019, 10:05 PM   #40
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Quote:
Originally Posted by 240-FAN View Post
Is there a simple way to measure/DIY to get the AFRs? Also, for exhaust temp, is it just using a hand held thermometer and pointing at the tail pipe?
AFAIK, exhaust temps are measured with some sort of test probe that gets stuck up your cars tailpipe. I would imagine that a hand held thermometer would work, just not sure how accurate since there are specific measuring instruments made specifically to measure exhaust gases that range in excess of 1000-1200F (diesels).

AFR gauges are nice because they allow you to monitor the AFR during driving.

Kits aren't too bad, price wise. I just bought and installed this one recently:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

I've bought this exact kit before and it works great. With my car, since it is KJet, I kept the existing narrowband o2 to keep the KJet brain happy. With yours I am not sure since it's LH. If I were you I would just keep both.

Installing an AFR/wideband o2 does not take but a half an hour. Just weld in a bung (usually supplied with the wideband o2) somewhere on the downpipe, if it's turbo be sure it's AFTER the turbo exhaust. Then feed the o2 harness through the firewall and wire in per installation instructions.
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Old 09-09-2019, 09:39 AM   #41
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Dang! I can give the infrared thermometer a shot on the exhaust temp gases. I am assuming I measure once the engine is at operating temperature?

Welding the bung for the AFR is a bit...ughhh...daunting for me given that I have no access to a welder and the last time I welded anything was in college a few years ago

Engine does have decent amount of blowby. The intake has oil in it....
FPR is new as of last year - replaced with a new Bosch unit as the old one had constant smell of raw gasoline. Would it be worthwhile to check the fuel lines on the sending unit?
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Old 09-11-2019, 10:31 PM   #42
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I was able to check the exhaust gas temp after taking her for a drive. It was about 110.3C
Is that within the normal range?
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Old 09-13-2019, 09:08 AM   #43
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Drove the car yesterday again. Guess what? Shaking, stumbling and shuddering from take off.
I'm planning on doing a compression test this weekend. Are there any tips on what I need to take into consideration?

Do I need to pull fuel pump fuse to prevent flooding while doing the compression test?
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Old 09-13-2019, 02:17 PM   #44
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I'd string a new circuit from the MAF to ECM with new terminals. Then replace the ECM.
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Old 09-14-2019, 01:52 PM   #45
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All 4 spark plugs are white and crusty - running lean I suppose?
The compression test results are as follows:
1. Cyl 1 - 164.5psi
2. Cyl 2 - 174psi
3. Cyl 3 - 179psi
4. Cyl 4 - 176psi

The test was run with the engine hot and throttle held wide open.
Also, when I pulled plug from cylinder 1 it smelt like raw gasoline.

Are any of these pointers to what the problem could be?
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Old 09-14-2019, 02:28 PM   #46
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That is an acceptable test. The main issue is probably elsewhere. Probably just got a bit of gas in there from the fuel being in the rail. Make sure you didn't change the plug firing order with all this checking stuff.
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Old 09-15-2019, 09:38 PM   #47
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Kinda late to this party but when was the last time you replaced the plug wires? Had a similar issue a few years ago. New Bougicord wires to the rescue.
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Old 09-16-2019, 09:00 AM   #48
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Good to note on the compression test results dl242gt.
The wires were replaced about in mid 2014, about 15,000 miles ago. The wire for cylinder 1 is super old though as that was first time I had changed spark plugs ever on any car and I messed up the grommet that sits over the spark plug on cyl 1. So the wire on cyl 1 is old.
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Old 09-17-2019, 04:31 PM   #49
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Quote:
Originally Posted by 240-FAN View Post
Good to note on the compression test results dl242gt.
The wires were replaced about in mid 2014, about 15,000 miles ago. The wire for cylinder 1 is super old though as that was first time I had changed spark plugs ever on any car and I messed up the grommet that sits over the spark plug on cyl 1. So the wire on cyl 1 is old.
Sounds like you know what to replace next. Report back.
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