1990 740 Turbo with LH 2.4
AKA Virgil because "he" is old and wise and reliable.

I'm fed up with my gas mileage. I'm also going to have time this summer to make some decent money and so I'll have funds to do fixes on my car that I can't during the school year (college, upcoming year 3).
New fuel filter, 15K old O2 sensor, Bosch platinum spark plugs, regular oil/air filter changes, 1 explained engine code. I am losing small amounts of oil. Around 1/2 of one quart after 3500 miles.

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All the rest of this is background information. Basically, I want to know where to check first for my poor mileage.
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I've had a check engine light for over a year. This is caused by my bad EGR temp sensor, and I've been assured this isn't causing my gas mileage. This will be replaced before two weeks pass.
The only reason I suspect it could have an effect is that immediately after clearing the code, my mileage drops. A lot say maybe 16 mpg. Then the code comes back and my mileage goes back up to 18-20. My air filters are clean, and my oil changes regular at about 3500 miles, but I'm behind on this one. The oil changes seem to have no effect.

On long highway drives at ~72 mph I get nearly 22 mpg. I drive 10 miles to town (and back) every trip and allow about 1 minute idle to warm up and I'm almost temp by the time I hit the 60 zone.
I lived at 4600 feet this summer as an intern in Yosemite national park and got 22-24 mpg all summer in mountain driving. We're talking an overall change of 6,000 feet over 30 miles and almost the whole time was spent in 3rd gear to prevent excessive up/downshifts in 3/4 gears. This is another reason I thought that my EGR was to blame for my bad mileage.

When I replaced my ozygen sensor right before smog check, I had 24 mpg from my first tank. I have never seen that again. My smog check came back great on everything buy Nox which was 3 ppm below fail. That's EGR related.
So, all in all my emissions are pretty good. My CO and CO2 were near 0 and .1 and the rest of the tests were below the average uotput.

I have no engine codes except the EGR. I have so far cleaned or replaced:
Fuel filter(new), EGR valve and pipes leading to/from it, throttle body, half my chassis from accumulated oil/dirt, tranny filter/passive fluid change (~5 quarts swapped), IAC valve, new O2 sensor 15K miles ago, all vacuum line with fuel resistant/reinforced (except for the turbo gauge that runs through the firewall), checked breather box to after-turbo hose (clear), and have somewhat used spark plugs(Bosch platinum 1's).
I have new front ball joints, shocks (boge turbo gas. Buy from FCPG. btw not IPD. They have them for about half price), uper mounting plates, boots, and bearings.

I suspect my fuel injectors are dirty. I have been running lots of chevron and seeing improvements in mileage with them... but it's within the error range of my calculations of mileage. Also I have a noisy external fuel pump - it quiets when I pull the fuse for the IN-TANK pump (sometimes and only in KP2/run). I did change the fuel filter recently. I'm going to try letting the pump housing dangle while I run the car and see if the noise is just due to contact with the body. When I changed the F. Filter, I tried to relieve the line pressure by sucking on the FPR (apparently, a human doesn't supply enough vacuum) and detected a faint whiff of fuel and a taste that hung around for a while.

I noticed my intake manifold is looking quite dirty. I need a recommendation on an all around cleaner for intakes. If I don't have to replace seals to do it, I will probably just remove the intake manifold and clean it with a toothbrush or somesuch. I don't like putting chemicals into my engine as I can't remove them.
I have zero mods/add ons. I do have my rear air dam (think bumper mud guard. Fits under the bumper to reduce drag) removed as Maaco decided bailing wire would work fine to replace the screws holding it on. They were right until the weight of the plastic caused the wire to cut right through it. I hate Maaco. I could write a post this long on why I hate them.

You don't need to read the following lists of problems and planned repairs, but it could be helpful.


My current problems:
-EGR temp sensor
-Radiator leak at seam. Loses less than 1 oz./day of normal driving.
-front wheel bearings are probably bad, having trouble finding out if I have
serviceable hubs or not. Looks like I'll have to actually open them up and
see.
-Takeoff shudder. Worse with more weight, especially in the back seat or trunk.
This seems suspension related. The bushing connected to the differential is
extremely bad - so bad I can see through the gap on the side nearest the
differential when the car is on a lift. This is my next priority after
radiator, etc...
-Time for a timing belt. I haven't had one done since the car came to me (at
least 30K miles) and I want it done so I know when it was done and can do it
again at 50K.
-Distributor leaking oil at head/dist seal, not the dist itself. Going to have
the cap and the rear seal replaced with the timing belt.
-Turbo blow-by. I've got oil passing my turbo and coating the inside of the air
hoses after the turbo. The turbo shaft has enough play to consider a
rebuild/replace at a later date (like when I have money).
-Recently discovered oil leak from back of turbo. There seems to be a lot of
oil dripping from the back of the turbo, down the housing and onto the
ground or body. I might have never noticed this - not visible from the top
of the car.
-PS pump shaft is loose, leaking. Going to replace with a warrantied reman'ed
unit belt is fairly new.
-Wonky roll-bar endlink bushings. All front swaybar bushings to be replaced
soon.
-Slightly warped front brake rotors. I get shimmy on brake, no pull. I think
the wheel bearings are making it seem worse than it is, but I'm not opposed
to new rotors for 120$.
-Turbo almost "spinup" at around 45mph//2000rpm. Barely audible whine, nowhere
near full spin. The new oil leak behind the turbo makes me think it could
be related to a not problematic wastegate.
*I Plan to replace the breather box. I don't have symptoms of poor ventilation,
but it's preventative maintenance.


If you read this far,
THANK YOU!
now that you read all that, why not post a response?

-Will

--
1990 740 Turbo, on its way to stock specs, maybe beyond

Proper NGK plug is BP6RES gapped at .028. Last time I bought = $2 each at NAPA.

Two things that got me the biggest improvement in fuel economy were:
- new air filter long ago on the '83 240; immediate 10% better highway MPG.
- new EGR solenoid on my 940 LH 2.4.

I, too, had the check engine light (MIL) go on in the 940, checked the codes and had the usual "fuel trim" readings plus one that indicated a bad throttle position switch. Fuel mileage was well down. Cleared codes and light - back it came. Checked all that I could with no improvement - gave up and went to the dealer. Dealer diagnosed a bad EGR solenoid (Calif. car with the ECU-controlled EGR). Lotsa $$, but no more MIL for 10k mi now, and a serious improvement in fuel mileage.

The Cat converter suggestion was a good one. If the car is putting any oil through the combustion chambers it can plug the converter fairly soon.
--
Bob (son's 81-244GL B21F/M46, dtr's 83-244DL B23F/M46, my 94-944 B230FD; hobbycar 77 MGB, and a few old motorcycles)

you might want to check your cat converter. Low boost and poor mileage.. check it.

Mike
--
In Tacoma '86 245 200K+ and '86 740T- 215K+ both with M46

lose the platinum plugs and get the CORRECT plugs in bosch or ngk. platinums do not work well in any application i see them sold for. easiest no start/hard start repair i do. plugs that cause that must be hard on mileage, also.

as a maintenance suggestion, replace the cap, rotor and wires. bosch for the cap and rotor, oe or bougicord for the wires-not bosch wires. again, too many problems for some reason. good luck, chuck.

I agree about the Bosch wires. I had an ongoing problem with my Volvo stalling every time it rained hard. Turned out it was the "cheap" Bosch wires I bought for $80. I finally got sick of going back and forth to the parts store with a so-called lifetime warranty. I bought OEM wires from the dealer and haven't had the problem since. Just FYI, the OEM wires do not come with a coil wire. It's sold separately. If you’re not in a pinch like I was, go with FCPGroton.com. They have 'em for about half the price I paid.
--
'85 760 5-speed manual 214K

Hmm... I'm having a similar problem with my ' 84 760 Turbo. My fuel mileage has dropped down driving to and from school (160 miles each way). It sounds like you might need a new fuel pressure regulator if you're getting fumes from that small vacuum hose. Mine is actually leaking now but I haven't gotten around to replacing it. I also believe that this is making my main fuel pump a little noisey (which is new). I wasn't aware that a 740 had an EGR valve. Maybe someone here can elaborate??

BTW, my turbo doing the same thing as yours (oil pooling in the duct work). I'm going to replace it with one from FCP soon ( around $600 I think). There's also a turbo rebuild shop near my home in Charleston, WV that I'm going to check with. Some people on the board say that a turbo can be redone for ~$300 if it isn't too trashed. I'm also hoping that this will help my MPG and oil consumption (1 quart per 400 miles of M1). Yours doesn't seem to be using nearly as much oil though.

Good luck with it.
Dave

First:

THANKS TO YOU ALL!

somebody left a snyde reply on another post "thanks for keeping it short.." lol and I thought that everyone else might agree.
The reason for such a long post is ...well mileage is a war of attrition. The details count.

I've been wondering just why plat plugs are worth a crap and I honestly don't know.
I'll try to replace them with my oil this week. I've got finals two weekends from now, so I might wait a little while.
I'm thinking the Bosch copper are fine? When I bought these plugs, I went to Autozone and they recommended the +4 because they're like 8$ apiece, but they were really no help. I bought the plain platinums because I didn't really know what to buy.

What are the proper plugs?

Also my turbo is really light on oil consumption, it just seems weird that it's dripping outside the turbo. I tried hard to keep my foot off it (I was pretty good, only two boosts in 150 miles). I don't have mileage figures yet.

The EGR sounds plausible, I think it might be part of the problem and I will replace it this summer when I can afford it. I have to buy health insurance this week. bleeuuugh.

I'll post back,
-Will
--
1990 740 Turbo, on its way to stock specs, maybe beyond