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I'm trying to help a buddy with his '92 740T. Here lately, the car will suddenly have a skip for an instant and then continue running fine, although when this happens at idle, often the engine will die.
When this happens, the tachometer dips, so I know it has something to do with the ignition system. I've swapped out the powerstage, coil, and crank position sensor with known good units and it hasn't made any difference. I checked all of the engine grounds on the car and they are good.
The only other thing that I can see that would maybe have an effect on the ignition system would be the knock sensor and I haven't tried unplugging it yet, but honestly don't believe that's the problem.
That leaves the EZK computer. Do these units go bad frequently? I've got an EZK from a '91 940T that I can try in it tomorrow.
This is driving me slightly mad...
I read through the FAQ and thought for sure that the CPS would fix the problem, but it didn't. BTW, he has the newer, white-banded sensor.
Any suggestions for something else that I might check?
Thanks!
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Any progress or new ideas? How's driving it with the new EZK?
Best Regards
--
1990 740 Turbo, on its way to stock specs, maybe beyond
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If you find it, let me know what the @#$% it is! Please :D
That's the whole reason I didn't take my 740T to college with me. An undiagnosed miss that wouldn't go away. (And then I lost the lower radiator hose, which I should have replaced, while going over a mountain >.< )
Does it only happen when the car's warm?
I replaced my CPS, to no avail - but it's not necessarily the same problem. I replaced the power stage, RSR, and the CPS because its wiring was split. The RSR should be jumpered to eliminate it, or replaced with a new relay - likewise the power stage should be either cooled down when the miss happens as a diagnostic test for heat-related issues, or replaced with new. One member said he carefully cooled it with running water. I would favor something like liquid nitrogen, or an upside-down can of computer duster, over water.
Can you check the timing? Mine dramatically improved when I disconnected the knock sensor, but didn't go away entirely. Checking the compression wouldn't hurt either.
If the new EZK box helps, I would be eternally grateful for the info. How many miles on your buddy's car? Mine's looking at 285009, but the EZK may not be original.
Best of luck!
--
1990 740 Turbo, on its way to stock specs, maybe beyond
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This car has about 250K.
Checking the RSR won't help from what I know with an ignition issue as the RSR is on the fuel side, nor will a compression test.
I verified battery voltage at the coil, but I do need to figure out which fuse is connected with the ignition system for power and make sure it's not faulty or is making a bad connection.
I have not checked timing, as on 2.4, timing is set. Again, being out of time slightly wouldn't cause the glitch that I'm seeing on the tach.
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I didn't know the RSR had anything to do with ignition either, but I've been told it can instantaneously cut off injector power, causing the car to miss a couple beats - and I think that would be enough to make the tach drop for a second.
Does it drop to the bottom, or just show an rpm reduction that would be expected with a significant misfire?
When I checked my timing, I was looking for weird things like way advanced or retarded timing at idle, timing moving when it shouldn't, and completely missing sparks.
I replaced my cap/rotor, but not my aged wires. It would be nice if it were that easy of a fix.
I also swapped in my coil from my 240 long enough to see if it made the miss disappear.
Grounds are important. Cleaning the one specifically for the coil wouldn't hurt anything.
Good Luck
--
1990 740 Turbo, on its way to stock specs, maybe beyond
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Have attacked this problem on my 1989 that landed in Boston for 12 years before moving to CA. FWIW
The grounding block in the bottom picture shows little bite, that is, scarring from the female spade lugs that would show up as gouges in the metal insuring a good metal to metal bonding. The tab on the left shows a possible indication or the tracks could be on the backside. Just a slight, extremely slight adjusting squeeze on the female lug curl can tighten it up so it goes onto the tab firmly.
Completely wire brush backside of the terminal block and the threads and underside of the bolt head to get the most contact surface possible, mandatory if you have stacked grounding blocks.
Preventative practice would be to give each the wire terminal end the quick tug test to eliminate a bad crimp to the wire or wire broken by flexing where it enters the terminal.
Bad grounds have more influence when the electrical system voltage is loaded down, so I always watch the system voltage when trying to find intermittent problems, a problem may show at 10.4 volts that isn't there at 13.4 volts.
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I really don't think that it's the RSR, as when I unplugged it and turned on the ignition, I still had 12V at the coil, but I might be missing something here.
After unplugging/plugging in the RSR connector a few times, we went for a drive and it did fine for about 20 minutes until we got back and then pulling into the parking space, it skipped and cut off. It would restart, however.
Just as a test, I plugged up a known good 148 EZK computer and am going to drive around with it to see if I can duplicate the symptoms.
I checked the grounds yesterday and they seemed to be good, but I can go back and clean/check all of the engine grounds.
The CPS that I put in it is a used unit, but it came out of a running car. Do they get flakey, or do they just die altogether?
Any other suggestions?
Thanks.
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"I really don't think that it's the RSR, as when I unplugged it and turned on the ignition, I still had 12V at the coil, but I might be missing something here."
You must have been at the Fan Control relay. They are the same and maybe close to each other. The green book diagram shows the RSR clearly inline with 12V (from Battery +) to Coil 15.
Green wire from RSR changes to Blue somewhere (Blue at coil 15).
The RSR is picked by Fuel relay output 87/2, so any glitch there would affect both fuel pumps and ignition.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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Bruce,
I'm familiar with the fan relay for the pusher fan on the 7/9-series cars, but I thought the relay for the fan was done away with when Volvo went to the electric cooling fan and its relay setup. Car is a '92 740 turbo.
I'll double check that I'm not looking at a different relay (the one that I'm dealing with has a large red and grey wire coming in/out of the relay plus the two switching wires for the relay. I'm fairly certain that this is the correct one as I unplugged the relay and the car died and wouldn't start, which shouldn't happen if the relay only controls the pusher fan (which this car doesn't have).
While I'm at it, I'll put in an extra fuel relay and I'm going to try to jumper the relay under the hood, assuming that it's in fact the RSR.
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"I'm fairly certain that this is the correct one as I unplugged the relay and the car died and wouldn't start,"
That must be the RSR. The red and grey wire colors are right. But before you said: "I really don't think that it's the RSR, as when I unplugged it and turned on the ignition, I still had 12V at the coil,"
Was that 12V at the coil a dvm meter reading? Could it have been a weak back-voltage via the ground side maybe? I'll bet a test light wouldn't light at Coil 15 with the RSR unplugged. Oh well, it was a long shot anyway.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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Is it possible that the problem is due to a flaky fuel relay? I'm not certain, but doesn't the EZK get it's power routed through it? From looking at the greenbook, it doesn't appear so, but at this point, I'm looking for other causes as I've swapped out every other thing that I can think of.
Bruce,
Yes, that's the RSR that I was referring to. I used a DVM to check for voltage at the coil.
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"Is it possible that the problem is due to a flaky fuel relay?"
• Yes possibly, to the extent that the fuel relay energizes the RSR, which powers the Coil in addition to the Injectors.
"I'm not certain, but doesn't the EZK get it's power routed through it? From looking at the greenbook, it doesn't appear so,..."
• No, both the EZK and the FI ECU get their main power from Fuse #1. The RSR only powers the coil and injectors.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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We'll see how it goes with the other fuel relay. If the old one is flaky, from reading Bruce's post above, that does seem like a way that the power could end up being cut to the coil, although I'm still not certain how I'm getting 12V at the coil when the RSR is unplugged.
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"...I'm still not certain how I'm getting 12V at the coil when the RSR is unplugged."
In some cases, a sensitive digital meter can mislead you. I can't explain it in detail (like Art B. could), but I suspect there's a stray trickle of back-voltage showing up on your meter, but without enough current to actually do anything. Think of six AAA batteries in series showing a nice solid 12V on a meter, but you could hardly crank the starter with it.
Your coil 12V reading (with RSR unplugged) would be a good application for a 12V Test Light. If the circuit is severely "starved" for current, a Test Light bulb will show it by being noticeably dimmer (or maybe not light at all), even though the meter indicates "all is well" with that +12V reading.
I've seen two first-hand cases of what I call "Ghost Voltage". The first one was on an AC compressor clutch circuit. The Low Side pressure switch plug showed an "incoming" 12V on one terminal, and "outgoing" one measured 3.5 ohms to ground (through the clutch coil). The clutch worked fine with battery 12V applied to the outgoing switch terminal, but did nothing when battery 12V was replaced by the meter's "voltage" reading probe.
Then, with 12V still showing on the meter, (probe still in the LS switch plug) I put a 12V Test Light on the meter probe and two things were observed:
1) The Test Light never even glowed.
2) The meter's "voltage" display disappeared.
That's what I call "Ghost Voltage".
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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