VS 97 strange problem - heres a challenge for the smart ones on here!!

[1997_equipe]

ok i have a vs series 2 v6. was duel fuel (factory) but its all disconnected now. has a new motor that has 140,00k that came outta same model car. since day 1 of putting it in it has the following symptoms:

Idles rough as hell sort of hunts for revs u can hear it trying to idle right but it cant
When u cruise it at 60 or 80 or 100 whatever it shudders and misses and runs like crap
When u thrash it it drives awesome
Sometimes it drives better than others
The longer i drive it, or let it idle the worse it seems to get
Occasionally i get an intermittant engine light that comes and goes
Surges when accelerating kinda stumbles then kicks in sometimes

Ive done:

Plugs
Leads
Coil packs
Fuel filter
Intake manifold gaskets
Injectors
Injector cleaner (bout 6 bottles over time)
TPS sensor
Coolant temp sensor
MAF sensor
And ive played around with vacuum hoses and charcoal canister (which seems to make no difference at all whether they are connected or not, could be a possible clue...?)

Im absolutely stumped
I will worship anyone that can solve this for me
I will not only worship but pay anyone willing to fix it for me

Spoken to a few different mechanics and cluey friends about this and everyone just scratches thier head and replies... "i dunno"

Please help lol its driving me crazy
Thanks.

[delcowizzid]

DFI module under coils or crank angle sensor

[1997_equipe]

i was thinking crank angle sensor... whats dfi module?

[bandit10]

i was thinking crank angle sensor... whats dfi module?

the metal plate that sits under the coil packs

[delcowizzid]

yeah ide do the cas first can cause shit idle and vibrations at cruise speeds but go good when on it and get hot when sitting idling and get worse the hotter they get

[HamaTime™]

Definately check your DFI Module, they can be a real culprit for shitty engine performance and rough idling. They can cause backfires etc etc. First place to look. If not then try your Crank Angle Sensor.

[Brett_jjj]

If changing the CAS and DFI module doesnt solve it. Then Id be checking all the wiring connections around the engine bay. If its been like it since the day the engine was re installed, then it might be a bad wiring connection somewhere. Carefully check the wiring connectors on all the engine sensors, and especially check the wiring connector that goes to the DFI module,the contacts inside this plug can get corroded and cause a bad connection,which can then cause it to run crook.Theres a small bolt that has to be removed from the connector before the DFI wiring connector can be unplugged from the DFI module.

[immortality]

i'm gona go left field here and suggest that you also do the O2 sensors. if these are old and stuffed they will screw around with the tune. a vac leak in the climate control (aircon) system will also screw with the way the car drives

[moff_man]

hows the gasket on the top of the inlet manifold the one on the top plate, is that sucking air. it sounds like its sucking air or the air flow meter is playing up.

also did you here the engine running before you put it in?

[Siggers86]

I would have to suggest against the O2 sensor, you would notice a fuel consumption increase and alot of black smoke at times, also poor performance would be fairly consistent, or you would get fluctuations if faulty, the crank angle sensor seems to be the corporate here, as when a motor idles thats when the knock sensor if out can cause you problems, as your rev the motor and give it some stick, the 'knocks' get unnoticed (if small) from a steady vibration, however the dfi module could also be the problem, I would do the knock sensor first, even a second hand one from the wreckers will work to see if there is a problem, also check its plug and wiring, then look into the DFI module however the wiring and corosion on cabeling would be advisable to check as well straight away, but a replacement isn't necessary unless there is visual problems, the usually corrode or get damage from a combination of heat and water from the radiator getting onto/in to it.
Another thing would be to put some high grade fuel in it and some octane booster, this would also help the knock sensor...

[astormsau]

What were the error codes? when the check engine light comes on you can bridge pin 5 and 6 on the diagnostic connector to find the error codes.
Crank angle sensor dying usually results in the car either cutting out when driving or not starting after the car has been run - its usually heat which causes it to play up.

My suggestions; read the engine codes and determine what the issue reported by the computer is, then take appropriate action. From the list of issues and repairs you have made i'd be suggesting oxygen sensors would help the situation but even at their worst, they will cause rough idle but not the shuddering you are talking about.

Get back to us with the engine codes...

[astormsau]

another possibility is the IAC - idle air controller, can cause issues with the car running like crap, as well as the TPS .. make sure they are all connected properly and clean....

[Brett_jjj]

The oxygen sensors dont even get used by the ECU (open loop) until the engine has warmed up and is up near its operating temperature.Then, the ECU goes into closed loop mode, and the ECU then starts to process the signals sent from the oxygen sensors to adjust the fuel/air mixtures etc.So if the engine plays up when its cold,you can rule out the problem being caused by oxygen sensors.

[immortality]

ecu goes into closed loop mode fairly quickly, that is why they used heated sensors

[Brett_jjj]

Ive checked this out on a tech 1 scantool, and even the heated 02 sensors still take a few minutes to switch to closed loop.Plenty of time to see if its running crook or not.Usually oxygen sensors wont effect the running of the engine that much.They mainly effect the fuel usage and economy,maybe a little bit of power,but they usually wont cause a misfire or really bad running..

[hako]

If you've never had this engine running properly since you bought it then it sounds like the motor was bad when bought. So what I'd do is a health check on the engine - screw all plugs out and check their appearance - then do a compression test, both dry and wet which should tell you the general condition of the engine. Otherwise, you'll just be replacing item after item and wasting many $$$$. You can buy a compression gauge for under $40 or 2nd hand or borrow one. If compression is good, check all ignition related items using check procedures outlined in the Gregorys manual (buy or borrow from library). Then do the same for the fuel system.

[immortality]

by then selves probably not, but on a older engine that isn't running right and a few other things not a 100% it will compound. speaking from personal experience here.

something else to try is a good old vacuum test. it will quickly show any major problems

also checking the actual fault codes might be a good idea. it might give a clue to where to look next

[immortality]

a dodgy fuel injector can cause similar symptoms too

[Brett_jjj]

Agreed,he says its done it since day 1 of putting the engine in.Id bet its either a bad CAS,the DFI module, or a bad wiring connection somewhere.Or lastly, Id try another ECU to see if that makes any difference.1997_equipe, youve replaced a lot of stuff there.It doesnt leave much more that could be wrong...Id be checking the above mentioned things next.

[Brett_jjj]

Yep,agreed, could be blocked injectors,especially if someone got/let dust or dirt get into the fuel rail connections while the engine was out. Would this cause the engine light to come on though? (EDIT) I can answer that myself when I think about it,it would, because it would upset the mixtures and readings on the 02 sensors and put them out of whack..

[1997_equipe]

its definately not o2 sensors coz the car still gets great economy like it should ad plays up warm hot and cold. the fuel injectors are good and fuel rail is clean i've checked these things already. im going to try the DFI module on sunday then if no success the CAS. ill let u all know how it goes thanks heaps for ur advice ur all legends

[immortality]

any updates?