LH2.4 issues with a stock B234F

Hi guys,

I've been around carb'd Volvos since I got my driving license almost 20 years ago, but I still need to learn alot about fuel injected cars. So that's why I'm here

I have a question for the LH2.4 experts out there.
I'm running a stock B234F in my Amazon wich has developed a problem with the fuel injection.

The symptoms are:

Sluggish power from standstill with open throttle.
Slight pops and bangs from the exhaust on the overrun.
Higher idle rpm when hot
Slow throttle response at lower rpm
Flooring it at lower speeds result in severe hesitation and (what I think) backfiring in the exhaust. Although I heard it once from the intake.

Things I have done already:

AMM is new and has been swapped over without any result.
TPS is new and has been adjusted accordingly
Fuel pressure regulator swapped out without result
O2 sensor voltage drops rapidly to absolute zero when applying throttle, but remains stable when at idle rpm. And it doesn't go over 1V (read with digital voltmeter)
At higher engine rpm it still goes as it used to, but it seems down on power when accelerating.
Fuel mileage does not seem affected.
Spark plugs are out and show grey/black deposits. they will be cleaned and regapped and put back in.
Distributor cap and rotor have around 5k miles on them. (will be checked later this week)

My guess is the knock sensor or engine temp sensor for the ECU, but other suggestions are more than welcome.

As fas as fault code readout goes there is an issue.
I'm running a Lh2.4 loom from a 240 because that was easier to adapt for my stand alone purpose. The diagnostics box is still there, but doesn't seem to do anything. (or I could be using it wrong)

Thanks in advance

https://ozvolvo.org/archive/
Search for "TP31361".
That is an LH2.4 Greenbook that will dive into diagnostic procedures for LH2.4 which may be of assistance for you. It is written for a 240, but LH2.4 works the same regardless.

I'd get the diag box working first -- it may not help, or it might mislead you, but it's a good start. If press the button, does the LED turn on? If not, you're missing +12v or ground at the box. With the probe wire in socket #2 (ECU), hold the button down for a long 1-second count, then count the 3 sets of blinks, hold the button down again and see if there's another code. If it's 1-1-1 then no codes are logged. Repeat for socket #6 EZK.

For LH2.4 wiring diagrams, I use the '93 240 Greenbook - TP32352-1 @ ozvolvo

A couple more questions - what Bosch part numbers are your ECU and EZK box? Do you have a VSS Vehicle Speed Sensor hooked up to the ECU from the rear differential sensor or from a front strut ABS sensor, through the speedometer?

Thank you for the reply. I'll get to it in the next couple of days and let you guys know if therer is any progress.

- popping and banging from the exhaust could be lean mixture. So that would suggest not enough fuel supply. Could be caused by a clogged fuel filter.
- if the engine gets too much fuel then it should be visible from the exhaust: black soothy. That could be caused by a broken fuel pressure regulator. The fuel gets trough the membrane of the leaking FPR and is sucked into the engine (uncontrolled) through the vacume line.
- other potential problems:
vacume leak somewhere between AMM and engine, leaning out AFR,
faulty lambda sensor leading to wrong fuel delivery,
faulty engine temp sensor leading to wrong fuel delivery.

Getting the OBD-codes should help you identify the issue with more accuracy

Thanks everybody for the help.
I learned how to use the OBD reader correctly and managed to diagnose the problem.

Turns out I had two issues: the first being a faultry lambda sensor (forgot the code) and the second one was a 3-1-1 code meaning a speed sensor issue.
I replaced the sensor and made sure the speed signal wire was ok.
Now she's running back as it should be.
Always great to know there is a awesome community to rely on when trying to fix problems.