3.5 V8 EFI - Lack of Power

edwardbahaw · Post by **edwardbahaw** » Thu Mar 08, 2012 1:50 am

Hi guys

Developed a problem yesterday with my 1992 3.5 V8 EFI Discovery. I was on the road when I suddenly experienced a decrease in power and the entire vehicle was vibrating.

I switched off and then when I switched back on it started but it did not rev up to 2000+ RPM as it usually does before it gradually drops to base idle speed. It just started and went straight to base idle speed. There is no knocking in the engine but it is vibrating a bit and slight misfiring sound is coming from the back of the tailpipe.

If I step on the throttle while on park it revs. If I put it in drive, it lacks power.

This vehicle has a new coil, new HT leads, new spark plugs and rove fine before.

I also disconnected the stepper motor and it did not rev up as I thought it should when this is disconnected.

Since it starts, I have ruled out the fuel pump.

I'm hoping that one of you great guys in here can give some advice on what to check next!

Thanks in advance.
Ed

ChrisJC · Post by **ChrisJC** » Thu Mar 08, 2012 7:59 am

I wouldn't rule out the fuel pump at all. Can you measure the fuel rail pressure?

Chris.

Ian Anderson · Post by **Ian Anderson** » Thu Mar 08, 2012 2:07 pm

I would start by resetting the ecu
Presuming it is hotwire

( bit of a mix early cars were 3.5 and tended to be flapper versions later cars after about 1989 tended to be 3.9 and hotwire ecu)

If hotwire

Disconnect battery for 30 secs

Reconnect and try again

It may be in limp hone mode

Ian

shaunod · Post by **shaunod** » Thu Mar 15, 2012 12:26 am

When you say 'disconnected the stepper motor' do you mean the electrical connection? or the air feed pipe? It does sound as though you have either an ECU flagged fault (could be a sensor reading out of range) or the stepper is not working properly. I think Ian is right .. reset the ECU first .. then start checking for dodgy input signals.