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Check the fuel pressure regulator isn't dumping fuel into the inlet manifold via its vacuum hose. This is a relatively common problem. Without oxygen sensors your ECU cannot detect over fuelling.
Wizard
SupporterThis one's got me stumped
Over the past couple of weeks the car has started running really rough and gulping down petrol like there's no tomorrow.
The car is a 1996 GEMS 4.6 petrol only (no LPG)
Symptoms, running rough, low irregular idle speed, struggles up to around 3000 RPM then appears to run smoother, very rich exhaust smell.
* I have hooked up the Faultmate FCR and no errors are detected.
* I have removed all of the spark plugs and they all appear the same black sooty appearance of an engine running too rich, but thankfully they are all the same!
* I cleaned the MAF sensor just in case it was giving false readings - no change
* As a long shot I plugged in the Bluetooth OBD11 and turned on the Torque Pro App. And it shows "open loop due to insufficient temperature". After driving for an hour in 35+?C there was ample time to get up to temperature!
image.jpg
* I have checked the temperature sensor output and the voltage varies with the engine warming up to eventually sit at around 1v at operating temp (as per RAVE).
What else can be checked that could be causing the problem?
Gary
AT REST
Check the fuel pressure regulator isn't dumping fuel into the inlet manifold via its vacuum hose. This is a relatively common problem. Without oxygen sensors your ECU cannot detect over fuelling.
Master
SupporterMaybe try cleaning the MAF sensor electrical connector plug with contact cleaner.
Could also be a faulty maf, do you have access to a known good one you could swap over?
Wizard
SupporterThanks guys. I'll let you know the outcome
Gary
YarnMaster
Subscriberx2 ...the rich exhaust smell and irregular running at lower revs is a sure sign... initially like the over use of a manual choke in an "old" car,Originally Posted by bee utey
In this case however, as revs increase, the availability of more air compensates somewhat for the over fuelling... hence the tendency towards smoother running over 3,000 rpm...
MY99 RR P38 HSE 4.6 (Thor) gone (to Tasmania)
2020 Subaru Impreza S ('SWMBO's Express' )
2023 Ineos Grenadier Trialmaster (diesel)
Master
Hi Gary,
Guessing you've tried the obvious - blocked air filter?
How about an air leak somewhere, although this would normally then run weak, but an easy check with a can of spray.
If it is down on power, the excess fuel maybe from just being heavy footed, so maybe sending you off down the wrong path.
I can't remember what mines like, but is it running on a dizzy, or is it coil packs like the later?
Could it be something silly like the timing?
I've got the nanocom if you want to try that.
Fossicker
My "new" D2 has similar symptoms and they found two faulty oxygen sensors when I had it serviced. Hopefully these will fix my problem when they arrive & are installed.
Fossicker
What's the fix for this particular problem with the fuel pressure regulator?
I'll probably mention it to my mechanic if the new oxygen sensors don't do the trick.
Swaggie
SubscriberTo me the most likely cause is simply that the water temperature sensor has gone high resistance either because of a dirty contact or stuffed sensor. This confirmed by the error message. The only way the ECU knows the temperature is from the sensor. It doesn't matter if its 50C outside!LOL
Try a new sensor first. Just to confirm AFAIR there should be 300 Ohms resistance at 82C plus so if it is 1000 Ohms or whatever, the choke is still on.
Regards Philip A
AT REST
A 1996 P38 doesn't have oxygen sensors and a D2 doesn't have an underbonnet fuel pressure regulator so the fixes are totally unrelated.
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