Problem Solved! '89 240DL (No Spark to cylinders 2, 3 and 4 at 2500 RPM)
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Problem Solved! '89 240DL (No Spark to cylinders 2, 3 and 4 at 2500 RPM)
The problem was that spark was cut off to cylinders 2,3 and 4 when the RPMs hit about 1800. Did a tune up (new plugs, new wires, timing, new mass air sensor, etc.,,,) and the problem moved up to 2500 RPM.
So, I had a chance discussion with a mechanic who hates working on Volvo, but who has seen this exact problem and figured out the cause and the clue was that the problem just moved to a higher RPM:
What is happening with this 240DL is that the signal to tell the ignition to fire went away at a certain specific RPM, Adjusting the timing only move the failure to a higher RPM. The conclusion was, given that no fault with any electrical or electronic component, was that it was mechanical. The question is what and how. The answer was simple, and mechanical.
In a nutshell, under ideal conditions, when the valves and crankshaft are at TDC, the rotor on the the distributor cap should point to TDC. This means that something was off. At low RPMs, the timing of the spark was sufficient for the engine and fuel delivery to be within operating specs and the various sensor signals were sent within the specs in terms of time. Obviously, at a given RPM, the signal to three of the cylinders stopped except for cylinder #1 (firing order is 1-3-2-4). At 2500 RPM, the spark only gets delivered to cylinder 1 until the RPM drops below 2500. Now add to this that the spark advance method and related devices bench check out as OK.
Now here's what was happening:
The Timing of the cam shaft was off from the crankshaft and hence the distributor cap rotor. Essentially, the timing belt was not installed properly by the previous mechanic and it slipped a tooth, the whole chain of events was off. It was within specs at low RPM but due to the spark advance system working properly and the timing belt being distorted, the error in the mechanical chain of events amplified as the RPM's increased because the cumulative error in the position of the crankshaft put the signal from the crank shaft position sensor beyond the set parameters of the electronic ignition module and hence, no signal from the CPS was detected.
All the individual parts were working according to design, but the valve timing was off only enough to cause the problem at a higher RPM.
All that is required to detect and solve this problem is to pull the top timing belt cover, rotate the engine to TDC and see if it matches up with TDC at the rotor cap. That simple. If it is off by more than a fraction of a degree, the valve timing needs to be adjusted via a new timing belt or proper tension adjustment.
So, I had a chance discussion with a mechanic who hates working on Volvo, but who has seen this exact problem and figured out the cause and the clue was that the problem just moved to a higher RPM:
What is happening with this 240DL is that the signal to tell the ignition to fire went away at a certain specific RPM, Adjusting the timing only move the failure to a higher RPM. The conclusion was, given that no fault with any electrical or electronic component, was that it was mechanical. The question is what and how. The answer was simple, and mechanical.
In a nutshell, under ideal conditions, when the valves and crankshaft are at TDC, the rotor on the the distributor cap should point to TDC. This means that something was off. At low RPMs, the timing of the spark was sufficient for the engine and fuel delivery to be within operating specs and the various sensor signals were sent within the specs in terms of time. Obviously, at a given RPM, the signal to three of the cylinders stopped except for cylinder #1 (firing order is 1-3-2-4). At 2500 RPM, the spark only gets delivered to cylinder 1 until the RPM drops below 2500. Now add to this that the spark advance method and related devices bench check out as OK.
Now here's what was happening:
The Timing of the cam shaft was off from the crankshaft and hence the distributor cap rotor. Essentially, the timing belt was not installed properly by the previous mechanic and it slipped a tooth, the whole chain of events was off. It was within specs at low RPM but due to the spark advance system working properly and the timing belt being distorted, the error in the mechanical chain of events amplified as the RPM's increased because the cumulative error in the position of the crankshaft put the signal from the crank shaft position sensor beyond the set parameters of the electronic ignition module and hence, no signal from the CPS was detected.
All the individual parts were working according to design, but the valve timing was off only enough to cause the problem at a higher RPM.
All that is required to detect and solve this problem is to pull the top timing belt cover, rotate the engine to TDC and see if it matches up with TDC at the rotor cap. That simple. If it is off by more than a fraction of a degree, the valve timing needs to be adjusted via a new timing belt or proper tension adjustment.
no mo volvo
Joined: Oct 2010
Posts: 11,289
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From: 37 North on the left coast
pretty sure I suggested you check the timing belt and the 3rd shaft that drives the distributor and make sure they were all phased correctly. but maybe I didn't actually write that down and just thought it, I'm not going back and looking...
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