Shocking Fuel Economy. What Sensors To Replace

[reeceo21]

Hey guys this has been bothering me for a while and i barely drive the car because of it. Its a 1990 gts4 with 200k on the clock. i get 250k's grandma driving and 200 with a bit of stick The computer has spat out NO error codes so im just going to replace every sensor with a brand new one. So far i have got on my list

O2 sensor- $98 (mechanic tested it and said its still working fine but bit of peace of mind)

AFM- $210 brand new. the car stalls quite often when slowing down and my idle is between 0-1200 when start up and then on some occasions it will just sit on 1000

TPS- Cant find. sometimes when i have been driving for a while the idle will stick at 1500. im assuming that is the TPS sticking ?

Coolant temp sender- $80 provided that rb26 ones fit. the needle always seems to be in the one spot

Thermostat- $50 piece of mind

Anything else anyone can think of. I have done fuel filter, fuel pump, tested regulator, changed plugs (all of them were black)

Cheers oh and if it helps im running BP ultimate.

[10 4]

tune?

[reeceo21]

Hmm perhaps, id there any tunes you can just buy ? I did that with my commy I sent my ecu and got it tuned

[mad082]

perhaps tell us how many litres you are calling a tank so we can see just how bad your economy is. may be that your economy isn't too bad and just your fuel level sender is the problem

[Moodles2]

It might be something as simple as the timing being out, whether the CAS is in the wrong position or the timing belt has skipped a tooth or 2, or perhaps whoever did the timing belt did it wrong.

I'd probably add getting those injectors ultrasonically cleaned if they are 200,000km old, I wouldn't bother with those fuel injector fuel additives.

If the plugs were black then it's probably running rich.

Get yourself a consult cable instead of blindly changing the coolant temp sensor, will also tell you if the O2 sensor is working, TPS, AFM etc.

[blind_elk]

Have you had the injectors cleaned? Have you cleaned the AAC valve? Have you cleaned / replaced the air filter?

Check the adjustment of the TPS. It also controls fuel cut-off during gear changes (when throttle snaps shut). (should be 0Ohms between pins 1&2 at "throttle closed", not 0 otherwise)

Could be a faulty temp sensor (different to the gauge sensor), which could be telling the ECU that the engine is still cold (should be 2.5kOhm when cold, 0.3kOhm at op temp).

[89CAL]

Mods on the car? Atmo BOV? Etc

Replace O2 sensor, check timing, reset ecu, put it on a dyno to check AFR's

[SKITTLES]

250k?

I wish I got that much in my gtst. I used to get 200 if I was lucky.

Then again, I don't drive like a grandma.

[reeceo21]

Have you had the injectors cleaned? Have you cleaned the AAC valve? Have you cleaned / replaced the air filter?

No but will now also get them tested. maybe they are stuck open ?

Yes i have very little change.

Yes put a fully hektic pod filter on

The timing belt seems like a large possibility. it is 110000k old. i have the kit i just need to get my full RWC done and ill get it changed any way of checking with out pulling the engine to bits moodles

?

MY mods are as follows. Stock BOV vented into the intake, 3" stainless from the cat, EL oxy sensor im assumming, put an aftermarket fuel pump in, FMIC, RB25 turbo, Torque split controller, and a whole bunch of things that i believe wouldnt affect economy. stock boost as well

I can tell its running super rich because ill choke if i have a wiff near the exhaust pipe

i can tell you that the fuel sender is not out ( i wish it was ) as i ran it to empty got 175k out of the tank and put in 45 litres of ultimate which was 70 buckers (((

I really appreciate the input guys. i hope to solve this problem and help lots of other skyline owners with shocking economy

[reeceo21]

Also would anyone be able to point me in the right direction on how to test all the sensors ?

[89CAL]

Hold up. Gts4 with an RB25 turbo?

Does this mean engine or just the turbo on the rb20?

And has it been bolted to an N/A engine if so?

[reeceo21]

It was an rb20det with an rb25 turbo

[89CAL]

Ok well that might be part of the problem. RB20 ECU's are alot more forgiving with non factory mods but because that turbo is pushing slightly more air then expected, your ecu might be adding to much fuel to compensate as a safety. Clean your AFM, replace your O2 sensor, check your filter, and do an ECU reset. This might help it

I'd still recommend Putiting it on a dyno to check AFR's at cruise and under load

[reeceo21]

OK update time

Spent two hours at the mechanics today learning sweet f a expect it runs rich as anything. Here is what was tested.

-Fuel pump and regulator, Very strong pressure and regulator was working fine.

-Coolant temp sender works but reads a little low apparantly.

-AFM is working in a operating range.

-Ground for the ecu and battery is good. though there was a piggyback wire connector on there for the sensors but nothing was on it ?

-Oxy sensor. Tried a another one his test tool and it was rich on idle and if the accellator was touched it would shoot to max. This pretty much did the same on my o2 sensor. he said mine looked reasonably new

-No error codes were present

-Injectors. Only tested the voltage and it seemed fine. he asked if they were aftermarket and i said i didnt think they had a red tab on them ?

-Throttle Position Sensor, He tested it and adjusted it.

So he reckons that there is a MAP sensor or a boost pressure sensor or something that maybe faulty. Can any one shed any light onto this ? He pretty much was clueless expect for that it was rich and that was the cause for bad economy. He reckons maybe there was a resistor of some sort maybe placed on the O2 loom. Can any one help or have any suggestions onto the causes of this ??

Any help is much appreciated. And Callen do you reckon a tune would be in order ? Can you tune for better economy

[reeceo21]

Oh and the afm was reading about 1.4 volts when revving it up. apparently in a operating range.

[reeceo21]

Oh and the piggyback was on one of the wires on the ecu. sorry for not making that clear

[blind_elk]

Unless you are doing highway miles, there is very little chance of the O2 sensor having any significant effect on your fuel economy.

What was the fuel pressure? Are you going to get the injectors flowed and cleaned?

[reeceo21]

fuel pressure was fine he tested it. he would clamp the hose and the pressure would go really high indicating a good pump. he said not to bother as they were working when it comes to injectors. they were working fine apparently and the problem is running rich

[Borci88]

Ive been having the same problem of 250kms to a full tank recently. I would average it out to 60-70kms per quarter of a tank. My mechanic reset the AAC and reset the idle and chucked in some Iridium plugs. I filled the car up to full and so far I've done 50kms and the needle has not even dropped below the full line yet, maybe this is worth a try.

[reeceo21]

Hey mate just threw in some platinums not long ago, made no change Cheers for the advice though will try cleaning the aac again though. odd how plugs made that much difference, they must of been burnt out pretty well