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Old 02-20-2021, 03:44 PM   #51
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Originally Posted by OldCarNewTricks View Post
The suggestion for use of a test lamp was very helpful, thank you. It simplified the process.
I'm glad that you got one and have been using it. "Batteries not required".


Post back when you get the thing running.
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Old 02-20-2021, 08:54 PM   #52
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Oh, I was thinking it was a little resistor, instead of a bigger wire wound resistor. I'd guess that the colors are yellow, violet (instead of grey), silver, gold, which would be 0.47ohms. This is still a pretty tiny resistance to be used in old designs. 4.7ohms (yellow violet gold gold) would be more common. I'd still get another ECU, and make the original a spare if you want to repair it later.
I took another look at it. I was wrong. The "grey" is actually the second ring that is discolored from heat. This resistor must have split open from heat. It's burnt. On the other side, what's left of ring #2 seems to be sandy brown colored. It seems to be about the size of a 3 watt.
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Old 02-23-2021, 05:14 PM   #53
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Woohoo! It runs. Turns out the ECU was the issue. Thank you to 2manyturbos for getting that replacement to me so quickly. Sounds to run a fair bit better than before, as well.
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Old 02-23-2021, 05:49 PM   #54
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Cool. Your test results pointed to the ECU. I'm glad you have it running now.
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Old 02-23-2021, 08:56 PM   #55
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Sounds to run a fair bit better than before, as well.

Might have the ECU for B23F higher compression engine:-)
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Old 02-23-2021, 11:23 PM   #56
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Drove it home finally. Bit sketchy with all the guage cluster lights out and the blower motor that died on me. But its home now, so time to get to work on all those smaller issues.
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Old 02-23-2021, 11:23 PM   #57
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Good diag. Glad to help. Thanks for posting back.
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Old 02-25-2021, 07:00 AM   #58
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Might have the ECU for B23F higher compression engine:-)

LH ECU is the same for high and low compression. 1983 is a 503 number, 1984 is a 510 number, I'm assuming because of the added circuit on 1984 cars for the heated O2 sensor. OP's car is an Aw70 car, if I remember correctly, so it's already a flat top piston B23F engine in there, unless swapped.



Ignition box is different on low compression engines. More aggressive advance curve.
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Old 02-25-2021, 10:32 AM   #59
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LH ECU
ECU table suggests 503 is for NA 1983/1984, but I've wondered if engine program was twitched between AW70 and stick versions...since engines mated to AW70 were higher compression on 1984 (on engine I own).

Increasing the compression ratio changes the mixture density, but knock sensor may compensate so lower/higher compression engines work ok with 503 LH ECU.

I do know a rebuilt 1984 B23F that was mated originally to AW70 works just fine when installed in a 1993-940 with Rex-Regina, using Bosch 0 280 155 746 injectors ; of course, a CPS was installed on B23F.
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Old 02-25-2021, 01:35 PM   #60
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ECU table suggests 503 is for NA 1983/1984, but I've wondered if engine program was twitched between AW70 and stick versions...since engines mated to AW70 were higher compression on 1984 (on engine I own).

Increasing the compression ratio changes the mixture density, but knock sensor may compensate so lower/higher compression engines work ok with 503 LH ECU.

I do know a rebuilt 1984 B23F that was mated originally to AW70 works just fine when installed in a 1993-940 with Rex-Regina, using Bosch 0 280 155 746 injectors ; of course, a CPS was installed on B23F.

Suggests is a good term. That ECU table is a crap shoot. Here is just one example of what I mean.

LH 2.4 -016 0 280 000-556 B230FD 1989 (EGR) 1989-1990 (EGR) - California / EGR Model: -937, -967 and -954 are suitable.

The B230FD didn't appear until 1993. A 556 is an NA 240-740 ECU with EGR. The suggested replacement ECUs are all 740-940 Turbo ECUs. The 937 and 967 are both non-EGR turbo ECUs. Suitable replacements would be a 933 or 946 NA ECU with EGR function. John is correct. 1983 US market NA 240s got the 503 ECU and 1984 got the 510.
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Old 02-25-2021, 09:56 PM   #61
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LH ECU...1983 is a 503 number, 1984 is a 510 number
Picture of LH ECU that came with my 1984 Volvo....not being used I assume whoever marked on it knew interchange aspect. Click on pic for enlargement.

OEM wiring diagram for 1993 shows O2 gets power via fuel pump circuit. I don't have a OEM wiring diagram for 1984, but it does not show a heated O2, just a single GRN wire going to ECU. I suspect this "1984" wiring diagram was not updated from 1983.

Logically, the fuel pump circuit would be used. Without tracing the wires, I suspect the "added circuit on 1984 cars for the heated O2 sensor" was most likely done via fuel pump circuit's hot side. So, 503 & 510 might interchange..Or at least 510 can do both years.

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Old 02-25-2021, 11:33 PM   #62
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510 works with 1983. That's what 2manyturbos sent me. So, you are correct! :D Also, the auto trans was swapped into the car, along with the rear end. The B23F is the lower comp, unfortunately. Doubt it makes a HUGE difference, though.
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Old 02-26-2021, 12:30 AM   #63
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510 works with 1983. That's what 2manyturbos sent me. So, you are correct! :D Also, the auto trans was swapped into the car, along with the rear end. The B23F is the lower comp, unfortunately. Doubt it makes a HUGE difference, though.
The higher compression 83s are slightly peppier. A very scientific term, I know.
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Old 02-26-2021, 01:03 AM   #64
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I wonder if it would be worth skimming the head before installing my A cam then...
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Old 02-26-2021, 09:12 AM   #65
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B23F
1984 Specifications

In-line, four-cylinder, B23F-LH Lambda engine with cast iron block, light alloy "crossflow" cylinder head, overhead camshaft, electronically-controlled fuel injection and closed-loop Lambda Sond emission control

Horsepower, SAE net:111 @ 5400 rpm (manual)
Horsepower, SAE net:114 @ 5400 rpm (automatic)

Torque, ft./lbs., SAE net:136 @ 2750 rpm(manual)
Torque, ft./lbs., SAE net:133 @ 3500 rpm(automatic)

Compression Ratio 9.5:1(manual)
Compression Ratio 10.3:1(automatic)
============================

Want more instantaneous power?

My 1993-940 (AW71L: B23F: Bosch 0 280 155 746 injectors; Rex-I/Regina) in a slow rolling start could leave many higher horsepower red-block turbos in my rear view mirror for a short while. None of my 240s had/have this amount of acceleration. Why...I suspect the MAP sensor (Regina) was a better sensor than AMM (Bosch)

Note - My B23F's head was shaved to max allowed, so I have a pinch higher compression, but I would not shave a good head...might be thinner head gasket out there.
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Old 02-26-2021, 12:28 PM   #66
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Want more instantaneous power?

My 1993-940 (AW71L: B23F: Bosch 0 280 155 746 injectors; Rex-I/Regina) in a slow rolling start could leave many higher horsepower red-block turbos in my rear view mirror for a short while. None of my 240s had/have this amount of acceleration. Why...I suspect the MAP sensor (Regina) was a better sensor than AMM (Bosch)

Note - My B23F's head was shaved to max allowed, so I have a pinch higher compression, but I would not shave a good head...might be thinner head gasket out there.
I actually have some of the newer style yellow body injectors to install in my 242. I've heard that the 4 hole nozzles can make for a good upgrade in the redblocks.

Do you have a B23F or B230F in your 940? I wouldn't be surprised if the better technology gave it the upper hand. You also have a lockup converter, which is probably pretty nice on the freeway.

Yeah, I probably shouldn't turn the drivetrain into too much of a project for this car. I'd rather be driving it than having it sitting idle in my garage for who knows how long.
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Old 02-26-2021, 04:31 PM   #67
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newer style yellow body injectors to install in my 242.
....B23F or B230F in your 940?
Those newer Bosch injectors run rich at cold startup on 240...I have to increase RPM for about a minute...then they are OK. On 1993-940 Rex/Regina, they work just fine on cold startup.

In this picture, it shows I had to fix CPS's mount to engine-block with flexplate below. A feeler gauge was used to measure distance from CPS to flexplate's teeth. Then, I center punched both holes, drilled it without CPS mount there, and tapped it. To drill holes, drill must be perpendicular to engine block...which means this was not done via hands, but a mounted drill, like this. One person on TB took block to a machine shop to do this.
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Old 02-26-2021, 05:34 PM   #68
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Those newer Bosch injectors run rich at cold startup on 240...I have to increase RPM for about a minute...then they are OK.
Good to know. I'll keep my old injectors around if I end up disliking the new ones.

Does the Rex/Regina system offer any advantages over the Bosch/Chrysler system? I know both are pretty reliable if well kept, and it sounds like the ignition curve is might be a bit more aggressive on the Rex/Regina.
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Old 02-26-2021, 10:42 PM   #69
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Bosch/Chrysler system?
Price wise, a map sensor is much cheaper than a Bosch AMM; and I've never had one fail on three different high mileage vehicles (2 Berettas, and one 940). I suspect sluggishness in Bosch's LH is due to an aging AMM, and/or a knock sensor not working.

MegaSquirt with a map sensor might be a better way than Rex-Regina long term. If I went down this path, I would firmly understand this topic: Spark Timing Myths Debunked.

RE: "ignition curve is might be a bit more aggressive"

I recall there are ECU/ECMs that can adjust spark timing for an individual cylinder that starts knocking. On Bosch's ICU (ignition control unit on LH 2.4), the LH 2.4 manual suggests it retards all cylinders if a knock is detected, and if this is not enough, LH adds more fuel. But, in service manual TP 31397, on page 31, its says "Retardation of the ignition in each individual cylinder is a feature of all systems equipped with knock sensors dealt with in this manual." Since this manual was published in 1989, I suspect Rex-I can vary ignition timing in each cylinder.

Volvo has used several different knock sensors, with a later version being a better design so a mechanic does not over-torque the bolt. Needless to say, if knock sensor is not operational, timing will be retarded some 10°
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Old 02-27-2021, 03:39 PM   #70
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Originally Posted by 84B23F View Post
ECU table suggests 503 is for NA 1983/1984, but I've wondered if engine program was twitched between AW70 and stick versions...since engines mated to AW70 were higher compression on 1984 (on engine I own).

Increasing the compression ratio changes the mixture density, but knock sensor may compensate so lower/higher compression engines work ok with 503 LH ECU.

I do know a rebuilt 1984 B23F that was mated originally to AW70 works just fine when installed in a 1993-940 with Rex-Regina, using Bosch 0 280 155 746 injectors ; of course, a CPS was installed on B23F.

Zero difference in performance. Took a M46 510 ECU from an '84 245GL and installed it into an Aw70 equipped '84 245GL. Ran the same as it did with the original box. The M46 car ran the same with the box from the Aw70 car, as well. 503 is the 1983 only box. 510 is the superceded part that replaced the 503 and added the circuit to run the heated sensor, as I suspect. Both like to fail, just like the pink label 556 and 561 boxes found in 1989-90 cars.


The ignition boxes are different, though. Early 1983 M46 cars with the "802" engine and all Aw70 cars received the 1317295 Chrysler box. Late 1983 and 1984 M46 cars received the 1346105 box, which had a more aggressive advance curve, which helped to counteract the lower compression and provided a B230-like 136 foot pounds of torque at 2750 rpm, instead of the 133 at 3500 for the flat-top piston block.


I also know that a factory rebuilt 1984 B23FT that was mated originally to Aw71 works just fine when installed in a 1982-242 with K-Jet, using Bosch 0 437 502 015 injectors; of course, a Bosch breakerless distributor was installed in B23FT.

Also, the early 1983 engines with the white cap distributor apparently have 107 hp, instead of 111-114 hp. Torque may be less, too.

Last edited by John242Ti; 02-27-2021 at 03:47 PM..
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Old 02-27-2021, 05:58 PM   #71
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more aggressive advance curve
Scanning advance specs sometime ago, yes, a wider advancement was used on some engines; off-hand, it would not be usual to see this on police type vehicles or special 'hot rod' versions.

But, premium fuel would generally be suggested/required, and if a knock sensor existed, it would kick butt when a knock is heard. IIRC, the owner's manual in 1984-244 with AW70 I drove suggested to use premium.

ECU/ECMs that can control knock in each cylinder can produce most power.

Last edited by 84B23F; 02-27-2021 at 09:16 PM..
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Old 02-27-2021, 06:02 PM   #72
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Footnote - Years ago on a policed based GM vehicle used where elevation differences ranged from sea level to 10,000 feet, there was a switch on the dash to change advancement; as altitude increases, fewer oxygen molecules, which means advancement change is required for peak performance.
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Old 02-28-2021, 01:27 PM   #73
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more aggressive advance curve
Article cited above explains how timing is related to fuel/air mixture, and compression. I highly suggest reading it.

RE: LH ECU...1983 is a 503 number, 1984 is a 510 number

I've not examined O2 sensor used, but its possible that O2 is grounded "actively" by ECU or via a grounding point elsewhere...chassis ground. If ECU is used to either ground or supply 12v, then an extra ECU circuit. But, based upon this generic 3-wire O2 sensor, no ECU design change was required...just a wiring loom change for hot and ground side for O2.

Bosch, like other companies, have changed part numbers on the same part design. Sometimes, its just a minor modification...better component design, etc. It could be the same part, but with a different program.
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