S/V/C70 Smooth start, then after 1 minute, runs rough with coughing under acceleration

Hi All,

Looking after a friends 1998 V70. It is a B5252FS (twin cam, 10 valve, NA engine). Have done the following:

1) Valve stem seals (I used the old rope down the spark plug hole trick so that I could do it with head in place...)
2) O2 sensor, MAF sensor
3) Distributor cap, and leads, rotor button.
4) Replaced timing belt (138 teeth....) and associated bits, etc
5) Cylinder compression varies from 155 to 175 PSI, so reasonable I am guessing
6) Chased down and eliminated all air leaks in the induction system
7) New PCV setup.


Initially, car ran brilliantly, (all one could wish for, but shortly afterward developed the following issue).

Currently starts easily, and runs perfectly with good power for about a minute, then loss of power, and struggles to accelerate, coughs and sputters. If the engine is left off momentarily (say a minute or so), engine again starts easily, and runs well for the same short period, before repeat of symptoms. These symptoms now consistent

There are no fault codes generated during this process (reads 1-1-1, its a Fenix 5.2, so I made up a LED test light system to read codes via the OBD2 port, and clear old codes).

Fuel pressure at start up reads 32 PSI, which seems a tad low, but car runs perfectly, then when car is allowed to continue idling as above, runs rough and the reading fluctuates a little, but ends up reading up to 41 PSI. I swapped fuel pump relay for a known good one, without effect. I removed the fuel filter, I can confirm that the flow through the filter appears excellent.

I am starting to think it may be the fuel pressure regulator.

Any advice would be greatly appreciated.

Cheers,

Richard.

Comments

  • FPR sounds a reasonable next step for sure
  • Following a chat with a fellow car club member, the crank position sensor was looked at, seems OK, but not ruled out.
    Cam position sensor on the other hand.... car behaves exactly the same whether it is connected or not, surely not a good sign, has anyone had a similar experience?
  • Ex850RSnoopy (@Ex850R) Somewhere Over the Rainbow. Melbourne.
    I thi K I had CAM POS sensor issue on old one of mine before and it's cheap fix
    cancer sucks
  • Possible that the Fenix system starts on block injection based purely off crank angle sensor and then changes to sequential after warm up
    egads
  • Possible that the Fenix system starts on block injection based purely off crank angle sensor and then changes to sequential after warm up

    Thanks Tim,
    pardon my ignorance of these matters, but does that mean that initially (say for the first minute or so) that the system runs on some pre-arranged settings, then switches over to what the sensors are reading?
    When I get home tonight, I will try to get some wires into the connection joints to hopefully enable me to take some readings that the sensors are giving out.

    Cheers,

    Richard.
    I thi K I had CAM POS sensor issue on old one of mine before and it's cheap fix

    Hi Snoopy, how did the cam position sensor problem manifest itself in your car?

    Cheers,

    Richard.
  • I had the same problem with my 850sedan .Changed plugs ,leads ,in desperation changed coil (made it worse) .Ithen rang Graham at Berry Motor Group wo advised me to change distributor cap and rotor button .A close look at the cap andbutton revealed nothing wrong but fitted new parts anyway.Instant problem solved.Apparently it is a common problem (I fitted a second hand cap and button ,problem remained)
    Ex850R
  • Ex850RSnoopy (@Ex850R) Somewhere Over the Rainbow. Melbourne.
    I had the same problem with my 850sedan .Changed plugs ,leads ,in desperation changed coil (made it worse) .Ithen rang Graham at Berry Motor Group wo advised me to change distributor cap and rotor button .A close look at the cap andbutton revealed nothing wrong but fitted new parts anyway.Instant problem solved.Apparently it is a common problem (I fitted a second hand cap and button ,problem remained)

    The obvious!
    Why do we complicate things....
  • Thanks for the feedback regarding the distributor cap/ignition components. I will refit the old cap and rotor button, in case the new ones that I fitted inadvertently caused the problem....... The old leads were completely cooked (leads 2 and 3 mainly), causing misfires, so certainly will not be refitting those..... Which is why I replaced the ignition components. Sometimes new is not better, will check later today.......
    I will also be purchasing a replacement crank angle sensor, luckily not that expensive.
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