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rough idle and hiccups during acceleration

T

Timmermans

New member
Joined
Nov 10, 2017
I have a 1992 volvo 240 manual with a B230FT motor and wasted spark setup. Lately the engine idles rough when warm, between 650 and 900 rpm. With the ac on, the engine sometimes almost stalls.

When accelerating hard the engine hiccups, holds back intermittedly, stutters, whatever you want to call it.

Sometimes I get a 121 AMM code. But I have read these don't have to be related directly to the amm...I have read these can also be produced when the mixture gets out of range

I don't know wether these 3 symptons are related and if they are mixture or ignition problems.

  • What have I tested:
  • AMM, values are good, also tested at the ecu, tested 2 AMM's https://ozvolvo.org/d/9733-bosch-lh-jetronic-24-ecu-and-ezk-pinout-tables
  • Spark plugs and wires and coil are new
  • Ingnition module doesn't get hot
  • No air leaks, did a proper smoke test, (throttle body shaft leaked, fixed this)
  • Fuel pressure regulator leaked a bit of pressure to the return line, had no residual pressure when shutting the car off. replaced this, no difference.
  • TPS sensor works, adjusted the sensor and the throttle body after fixing the shaft seal
  • Tested another ECU, no difference
  • Coolant temp sensor values are good at the ECU
  • ECU plug/pins pass the drag test
  • Knock sensor values are good at idle, didn't test these with wide open throttle
  • Injectors dont't leak at 3 bar fuel pressure
  • Replaced the fuel filter
  • Deatchwerk DW100 intank pump only, 2 years old, works well
  • Lambda sensor tested at sensor and ECU, works well
  • Intake hoses are silicone, no collapses.

I have this setup for 6 years, but never had this problem. Where can I look next? Going on holiday in a week and want to have the issue fixed!

Google gemini suggest the following:

1. AMM Wiring & Ground Shielding (Wasted Spark Interference)​

You tested the AMM and the ECU pins, but did you test them while wiggling the harness?

  • Volvo 240 harnesses are notorious for internal wire degradation near the AMM connector.
  • Furthermore, wasted spark coils output massive amounts of Electromagnetic Interference (EMI) compared to the stock distributor. If your AMM signal wire (which is shielded) has a degraded shield ground, or if the wasted spark wiring is routed too close to the AMM harness, the EMI can corrupt the 0-5V AMM signal under load. This will instantly trigger a 1-2-1 code and cause the ECU to miscalculate fueling, leading to a stall/stumble.

2. Spark Plug Gap and "Blowout" Voltage (The Stutter)​

You mentioned the new plugs are gapped to 0.7mm. While 0.7mm worked great on your old, worn plugs, new plugs have sharp, crisp edges on the electrodes that actually change how the spark jumps under pressure.

  • Under heavy acceleration (Boost): High boost creates massive cylinder pressure, which dramatically increases the electrical resistance inside the combustion chamber. If the gap is too wide (0.7mm is right on the limit for a wasted spark B230FT), the energy required to jump that gap skyrockets.
  • The Result: The coil has to work twice as hard to discharge. This causes spark blowout (the stutter). More importantly, because the coil has to build up a much higher voltage to jump that 0.7mm gap under boost, the Electromagnetic Interference (EMI) radiating off the plug wires increases exponentially. That sudden massive spike in wireless EMI is what is blinding your AMM wire 8 weeks after the change.
  • The Fix: Regap the plugs down to 0.6mm (0.024"). This lowers the voltage threshold required to fire the plug, stops the blowout, and instantly reduces the amount of electrical noise radiating into your passenger-side engine bay.
Does this sound logical to you guys? When I did the swap to the B230FT, I just put the AMM/Ignitor/Bosch 2x2 coil wires throught the same grommet through the firewall.
 
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The AI response is confused, and doesn't match your symptoms.

~6 years without problems suggests that something changed, and that the initial setup was fine for a long time. When did you first notice symptoms? Was it gradual, or all at once?

A failing CPS can cause spark problems before it eventually becomes a no start.

Try a power balance test - when warmed up at idle, unplug one injector at a time and see if they all behave about the same. If one causes no change, then you're looking for a fuel/spark/valve/etc. issue for just that cylinder.

Are you running standard resistive plugs (the R in the part number)? And standard resistive plug wires?
 
I always had a slight hesitation when going through the revs, but nothing alarming. The change came when i changed the plugs, wires, and coil about 6 weeks ago. I use standard 940 wires and NGK BPR7ES plugs. When searching for the problem, I fixed all sorts of small things. Like Vac leaks, FPR return line leak.
 
16T turbo with the wastegate set at 0.8 bar. Bosch 0 280 155 759 injectors. A camshaft, 3 inch exhaust, adjustable camshaft pulley, advanced about 2 degrees. rest is mostly stock
Now that i think about it, since the B230FT swap, I always got a 144 fault code at the EZK, load signal missing. I was never able to get rid of this, because the car mostly ran fine, I just went on with my life. I wrote about it here: https://turbobricks.com/index.php?t...signal-keeps-coming-back.364783/#post-6368815
 
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Hiccups/hesitation at heavy and WOT. Before fixing the vac leaks and FPR it also had the hiccups at light throttle.
 
Do you have a wideband? All of this sounds connected to me, the 1-2-1, 1-4-4, and the hiccuping. Did you test the AMMs (I assume they're -016s) by measuring voltage and comparing what it should be or did you try them, install and drive around? Are they real Bosch units?

Does it sound crisp at WOT or muffled, like the exhaust note is dampened?

My 2000 mile diagnosis says that your load signal is messed up, AMM or wiring or ECU, and it's putting the fuel to it, giving you the hiccup. Now that there's an idle concern, I'm leaning toward AMM but you might feed info that makes me say no.
 
I don't have a wideband unfortunately. I measured the amm (016) signal voltage at the amm and at the plug at the ecu, at idle and with some throttle. Values were in spec. Both Amm's were the same. Both are original Bosch. Around 3 years ago I replaced the EZK for another one but the 144 code kept coming back.

I didn't pay attention to what it really sounds like when it happens. It definitly doesn't sound like pinging/detonation, I know what that sounds like.

I used the original 1992 240 loom when doing the swap. So I moved the Amm from the driver to the passenger side.

Thank you for thinking with me!
 
Well, if you TRIED them (plugged them in and drove around with no change), then don't. You're saying you measured them. They can fail in peculiar ways and MIGHT measure out ok but drive poorly.

Also, do you still have the old ignition components?

When you moved the AMM, did you pull the wiring out of the vinyl tubing and re-route it, or did you cut the wires and splice in?
 
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Timmermans said:
16T turbo with the wastegate set at 0.8 bar. Bosch 0 280 155 759 injectors. A camshaft, 3 inch exhaust, adjustable camshaft pulley, advanced about 2 degrees. rest is mostly stock
Now that i think about it, since the B230FT swap, I always got a 144 fault code at the EZK, load signal missing. I was never able to get rid of this, because the car mostly ran fine, I just went on with my life. I wrote about it here: https://turbobricks.com/index.php?t...signal-keeps-coming-back.364783/#post-6368815
Click to expand...
According to the Bentley Manual, and https://www.volvoclub.org.uk/faq/EngineOBDCodes.html , the 144 fault should turn on the check engine light. Is your CEL always on?

I don't know what the EZK box does if the load signal is missing completely, or missing intermittently. It might pick a default load value and use that instead to determine spark advance, which is certainly bad for at least part of the operating range.

Why did you replace the ignition components?

shoestring - do you know how the A cam should idle with Timmermans' setup? Is it usually smooth, or somewhat rough compared to a factory T cam setup?
 
So i went on with gapping the plugs to 0.6mm (0.024 inch). just to try something non invasive. when I got to the 4th plug, i found this:1000037108.jpg
What the hell...

Bought a new plug, gapped it to 0.6mm, because I didn't feel like pulling the other plugs again. Drove untill it's warm. And of course, this was the problem since changing the plugs. Steady idle, no more hesitations! No clue why this happened, but it did. Drove for 40km today, no fault codes yet. Only thing is, the car feel a little bit more sluggish now. Maybe this is because of the 0.6 gap?

As to the 144 code which I got the last 6 years intermittendly, I never got a CEL light with this. I just checked the diagnostics box every once in a while. When I get the code again I will start with routing the ignition wires more neatly separate from the main/amm loom. I will post this in the original 144 fault code thread. Thanks for thinking with me guys!
 
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bobxyz said:
shoestring - do you know how the A cam should idle with Timmermans' setup? Is it usually smooth, or somewhat rough compared to a factory T cam setup?
Click to expand...
A cam will compromise idle quality compared to T. It won't be terrible, and at this boost level, I wouldn't sweat it.
 
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