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Old 08-13-2019, 02:52 PM   #1
dauer
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Default '91 745 turbo, intermmittent power loss then no start condition

Hi Folks.

As the title states, I experienced some intermittent power loss while driving yesterday morning then when I got in my car to head to lunch it would crank but not start. It tried to start a couple times but now, nothing. Prior to this my car's idle speed would occasionally/randomly increase to approximately 1500 rpm, if I turned it off then restarted the idle speed would return to normal (about 750-800 rpm). It has been exhibiting this symptom for a while.

Here's what I've confirmed or replaced thus far: noise suppression relay, fuel pump relay, crank position sensor, cap and rotor, cleaned IAC valve and MAF, confirmed it has spark, confirmed it has fuel by pulling fuel supply line and cranking (a healthy stream of fuel flowed), spark plugs are perfect, confirmed injectors and IAC are working via control function 3 in green Volvo LH2.4 book. It will fire up on starter fluid but won't remain running.

That leads me to control function 2 in the green book which tests the TPS. I can only get the diode to flash the 3-3-2 sequence no matter if the throttle is open or closed, although it always returns to rapid flashing which signifies an error code. I did confirm the TPS "clicks" when the throttle is opened and I checked the resistance at the TPS using info from a different message board (the horror!) and it yielded inconsistent/incorrect results.

I'm not very experienced in trouble shooting ignition/fuel problems but based on my findings I'm leaning towards the culprit being a faulty TPS. My questions are as follows: Does my assumption seem logical? Should I test anything else? Is it typical for a faulty TPS to cause a "no start" condition? Thanks.
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Old 08-13-2019, 03:29 PM   #2
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TPS won't cause a no start.

If it runs on brake cleaner that means ignition is OK and you gotta diag fuel.

Do you have a test lamp?! I would be checking next for power to the injectors. A noid light is great for checking for injector pulse. A test lamp works too. Get one for $15 at the parts store.

The "radio interference" relay powers the injectors. Those, and the wiring fail.
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Old 08-13-2019, 03:45 PM   #3
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Can you confirm that it only has that one code stored in memory? If you repeat the procedure it will cycle through all the codes. What you describe sounds to me like a dead crank position sensor or MAF. You can also run the car with the TPS unplugged altogether if that's what you are dead set on, but as Zach mentioned, a failing TPS will not cause a no-run condition.

Verify that no pins are backed out as well.
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Old 08-13-2019, 04:00 PM   #4
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Does it have a strong smell of fuel/gas?

Is there gas in the oil?
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Old 08-13-2019, 04:20 PM   #5
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Okay. So it's probable that it's not the TPS then. I've replaced the crank position sensor with a new one I keep as a spare.

I don't have a noid light to test the injectors but running the "control function 3" you can hear all the injectors clicking. Would this rule out faulty injectors or faulty power supply to injectors?

I had a new noise suppression (radio interference) relay, I swapped that at both relay locations (chances are both of them didn't fail at the same time).

There is not a strong odor of fuel or any for that matter. I pulled the vacuum line off the FPR and it is dry and does not smell like fuel. The oil is clean. Also, there is no CEL. The MAF was replaced about 100k miles and 19 years ago (car has 160k miles on it now). I'm sure the lifespan of MAFs vary greatly but is there a test procedure for them? Thanks.
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Old 08-13-2019, 04:45 PM   #6
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Also forgot to mention that prior to this no start condition my car would long crank before it fired up. Especially when sitting for a period and engine was cold.
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Old 08-13-2019, 06:10 PM   #7
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You need a test lamp. Injector click on OBD mode isn't a good test. One guy here recently had rotten injector wiring at the ballast pack and had injector "click" on OBD test mode but inop injectors during cranking.

Again, if it runs on brake cleaner DO FUEL SYSTEM DIAG. Fuel pressure and injector pulse should be tested properly.
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Old 08-13-2019, 09:24 PM   #8
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I confirmed the injectors have power to them using a test lamp. Couldn't test the pulse because I didn't have a helper to crank the car while I probed. I suppose I'll need a fuel pressure test kit to confirm proper fuel system pressure. Unfortunately because it doesn't run I'll probably need an extra set of hands for this as well. Does this seem like a reasonable course of action? Thanks again.

Last edited by dauer; 08-13-2019 at 09:32 PM..
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Old 08-13-2019, 11:37 PM   #9
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No helper is needed. Apply 12v to the starter solenoid with a length of wire. There's a small blue/yellow to the starter- apply 12v here.

Backprobe the test lamp between the injector terminals. Key ON...crank...

Blink?




Can you keep it running PULSING brake cleaner into the throttle??

We drive trucks with dead fuel pumps into the bay with a man riding under the hood pulsing brake clean into the throttle. The other man is Wheel Man.

Last edited by ZVOLV; 08-13-2019 at 11:50 PM..
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Old 08-14-2019, 01:09 PM   #10
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I was able to get it started using starter fluid and keep it running for a little while by manually opening the throttle at the throttle body. It ran very rough and would not idle at all. Unfortunately while I was doing this I noticed that the PS/water pump belt was very loose and misaligned. Upon further inspection and while attempting to tighten the belt I discovered that the power steering pump was missing two mounting bolts...awesome. Well that turned into a three hour distraction but I got it sorted...back to the task at hand.

Seeing as I can keep it running long enough to test the pulse of the fuel injectors, this is next step. My question is which wire do I probe? All the injectors have a green and white wire, when I test for power supply (test light clip on negative battery terminal, ignition on), probing both wires results in the test light illuminating. Any idea what wire I should probe to test the pulse? I don't want to probe the wrong one and damage anything by sending 12v back into it (unsure if this is even a concern).
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Old 08-14-2019, 03:28 PM   #11
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With computer circuits, a high impedance test lamp should be used. (Approx 14 ohms). But since your car has a resistor pack, I don't see why a low impedance test lamp couldn't be used.

I would backprobe between both terminals of an unplugged injector connector. Crank and it should blink.

I think these engines should stay running with brake cleaner pulsed directly into the throttle body.
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Old 08-14-2019, 04:51 PM   #12
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Firstly, thank you for all the information. I fear my inexperience may have caused further harm. Reason being is that I used a test light that was not computer safe and I also back probed the connector without unplugging it (did that before your last reply).

Hopefully the inadequate test light is not a problem as you stated. But what about the back probing the connector without unplugging it? Time for a new ECU? On a related note I purchased a noid light kit. Results: no blinking on any of the connectors while cranking. I would say that we're moving in the correct direction but now I'm concerned that I may have caused this condition with my amateur diagnostic work.

Also, I can no longer keep it running at all by manually turning the throttle plate. Unsure if that's pertinent information?
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Old 08-14-2019, 06:07 PM   #13
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Disconnecting the connector just eliminates the component from the circuit.

Backprobe just prevents damage to the terminals. I front probe only with the proper test probe. Stuffing meter leads into the front of terminals is a bad idea.

It's difficult to tell what's going on, but I would now connect the test lamp between coil negative and ground and then check for blinking.

This sounds like a possible crank sensor issue. I would inspect it and wiggle things around and see if it starts. You can also measure resistance between the correct two pins and see if it's an open circuit.

Last edited by ZVOLV; 08-14-2019 at 06:13 PM..
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Old 08-14-2019, 10:20 PM   #14
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Phew, that's a relief. Thanks. Put the tools down for the night, going to take another stab at it tomorrow. I did replace the crank position sensor with a new one but that doesn't necessarily it's not the issue. I'll report back with my findings.
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Old 08-15-2019, 10:31 AM   #15
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If the new crank sensor was one of those $8 deals than there’s a good chance that could be the issue, which would be good it’s an easy fix.
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Old 08-15-2019, 02:09 PM   #16
dauer
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I don't recall how much it was but I do remember it was from Dave Barton's site and it was certainly more than $8. I do know that the lh2.4 has a test mode for the CPS which I will conduct later (at work now). The tach does jump when you crank it which I've read can be an indication of a "good" CPS also. All I know is I'm starting to get discouraged. If any fellow TBer's are in the general vicinity of Asheville, NC and willing to lend a hand I will gladly compensate you with monies, beer, food or all of the above
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Old 08-15-2019, 04:53 PM   #17
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Do you have pulse at the coil negative??!!
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Old 08-15-2019, 09:01 PM   #18
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Confirmed pulse at the coil negative. Reconfirmed the injectors have power but still no pulse signal. No other stored codes from the OBD port. Although I couldn't find the test procedure for the CPS, although given that the coil has pulse I'm guessing we can rule that out as the culprit?
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Old 08-16-2019, 02:31 PM   #19
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Ok so you have traced the problem down to a fuel related issue since it runs on brake cleaner. You are close! Don't give up.

The engine should stay running on brake cleaner.

Crank sensor may still be bad. A scope could be used, a meter to check resistance, or AC voltage works too. I would focus more on the fuel system at this point.

So your computer is giving codes on OBD terminal 2, right? Pin 6 is EZK. If codes are present, that means the computer has good power and ground.

You need to figure out why you don't have injector pulse. If I had your car, I would go to the ECU and confirm signal INTO the ECU. The LH box receives some type of signal FROM the EZK ignition box. As far as which terminal and what type of signal it is, I don't know. Sorry. You also need to check for less than 2 ohms between the ECU and the injector negative terminal. There possibly is an open circuit between the ECU and the injector control side of the circuit.

If the LH box has good power, ground, and signal IN, but no signal OUT to control the injectors, it is time to install a LH box. At your skill level and tool level, it may be worth trying a new LH box.
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Old 08-16-2019, 09:24 PM   #20
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Wow, that's all very helpful and informative. Thank you. My ECU is in fact giving codes on terminal 2 of the OBD. I've got some time this weekend so I'll try to dig into it.

Also, pardon the ignorance but when you say the LH box are you referring to the ECU?
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