stateofstatic

Was getting about 10.5 combined city/hwy mpg in my stock 92' XJ sport with 100k miles, chalked it up to crappy winter gas...until I noticed a light gasolene smell after starting her up in the garage before opening the door up.

Figured the fuel injectors might not have a good seal and are leaking gas through dried o-rings, so $90 later for a set of ultrasonic cleaned bosch 4 hole fuel injectors, new lubed o-rings, a new NTK O2 sensor (only $21 at rockauto so I figured why not), an ECU memory clear and reset, and my first full tank of gas has netted 24.6mpg!!! Obviously I need 3-4 more full tanks to get a better average, but at this point the ECU is still in learning mode (runs richer) so it should get even better mileage as this progresses.

So for anyone having poor MPG issues, this might be worth doing in addition to checking the basics (vacuum lines, cracks in manifold, etc.)

Password12345678

That's great! I have a 98 stock and I only get around 12 combined, though most of my driving is done around town... Maybe I'll try this.

DFlintstone

In my experience, (got a bit of it), going to four hole alone may or may not get one more MPG. There ARE other advantages, idle and throttle response are nicer. The one time I saw 24 MPG in my "brick-mobile", was a rare trip 200mi. south down hwy 101 with a tail wind pretty much the whole way.. Even with all about perfect, a new NTK o2 sensor and ideal Bosch 4 hole injectors, mileage drops to 16-18, (or less) "knocking around".

PatHenry

I'm going to guess the new NTK O2 sensor is the main factor in improved MPG.
Is yours a 2wd or 4wd? Auto or manual?

I was able to get an avg of 20-ish in my 95 5-spd 4wd in the summer with heavy highway driving and zero extra idling. This time of year I'm getting 16.5 avg with the crappier gas and a fair amount of extra idling.

I've been eyeing the Bosch injectors, but mostly due to the idle being rougher than I'd like. Where did you get the refurb injectors for that price? I'm seeing prices at 160 for the set.
I am hearing a slight whine - like a bearing on an accessory - at first start of the day. It's so minor I haven't yet investigated it, but if it turns out to be the water pump, I may go ahead with the timing chain replacement that I've considered first, but if I could do injectors for under $100... maybe I could do both without upsetting the wife...

Scott91370

Remember that replacing any old part with a new part is going to help mpg. I would hesitate to say that it is because they are 4 hole injectors that it si giving such better mpg but because they are new and clean is probably what helped as well as a new/clean O2 sensor.
I'm not saying "do not buy these because they aren't better'. I'm saying of course it helped, they're new. Just like when E3 replaces the old spark plugs and claims 15% increase, how many miles and how far out of spec were the old pugs?

All that, the replacement engine will probably get a set of 4 hole injectors just because of age of originals.

downs

I did 4 hole injectors and still get 13.8 MPG average even with mostly Highway running back and forth to work I just ordered an NTK O2 sensor to swap out with the less than 6 month old Bosch I put in, in October lol.

stateofstatic

4WD AW4 Auto in 2WD all the time.

The injectors I got from an ebay seller that seemed legit...here was the description: “Set of 6 Genuine Bosch 0280155703 4 hole fuel injectors. They are externally cleaned, disassembled, and checked thoroughly for damage. They get ultrasonic cleaned from all deposits that form inside the injector which restricts nozzle operation. They are then flushed off any broken up deposits from the ultrasonic cleaning. Each injector is then bench tested for flow under full load and a wide array of speeds to make sure it's working properly. Based on the flow measurements they are grouped into 1% flow matched sets. The injectors receive all new parts such as pintle retainers, filters, bushings, and o-rings.”

Got them for $93, though I just checked the guy's current listings and they're now priced at $135...user name is ACAM68.

One thing to note as an update that I did yesterday: I warmed her up for 10 minutes, took off the air inlet flex pipe to the throttle body, then poured a can of Seafoam down the throttle body slowly while pulling on the throttle actuator to keep the RPMs high so that it wouldn't stall while dumping in the Seafoam. Then when the bottle had about a quarter or so of liquid left in it, I dumped the rest in all at once to flood it and kill the engine. Then I let it sit for 15 minutes, and fired it back up...MASSIVE smoke show for a good 3-4 minutes, which is all the carbon gunk burning off from the top end of the engine. The end result? Throttle response improved, and on a flat road my cruise RPM at 35mph went from a steady 1500rpm down to around 1300rpm...and that's on top of lowering my tire pressure from 50psi down to 30psi (so the gf won't complain as much about ride harshness). I'm betting this will improve city-only MPG pretty decently, but time will tell.

mcnerd

I got mine hear.... Great success a Renix. Your mileage may vary....

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F20 0902253274

DFlintstone

I don't have my normal stuff handy. Post 90 the 703's will work fine. Do note that there are now other options with more holes and finer amortization of the fuel. (that's good!). Pre 91 they also work fine with an exception. An 87-90 Renix will run on pre-programed defaults until the puter gets on board and starts controlling the pulse width. Call that (closed loop). Not really a big problem, BUT!!! If there is an issue with the 02 sensor, or it's heater or wiring, or If you start your day dropping down a steep hill, (say dropping 1,500 feet in 3 miles, in ten minutes, using the engine as your brakes), it will run rich, (which doesn't help it heat up with all that extra fuel evaporating and robbing heat). The mileage tanks there of course.

The Bosch 746 on the other hand, (for 87-90) will be closer to correct in open loop.

The Map hashes out a rough approximation for fuel by sensing intake manifold vacuum, more foot, less vacuum, then more fuel. A leak to the MAP vacuum will make it think you got her floor-boarded and it will increase injector pulse width. Once all is "on board" the puter will read and adjust all sorts of things.02 sensor, engine temp, throttle position, timing, rpm. Lord knows what else, then "trim" the injector pulse width/(mixture) best it can for optimum mileage.

97grand4.0

X2 on the O2 sensor. I have one NTK on the desk here now ready to go in. Been putting it off because I think I may destroy whats left of the f ront pipe in the process, but have torch and will try. I unplugged my sensor and got better mileage and performance been waiting to stuff this in. Have the 4 holes already in.
You can pretty much tell by the fuel trims. Should be around 0.0. If you have negative trims, it means the pcm is taking out fuel because it is not seeing enough oxygen, because the sensor is clogged up. Lean running is worse than rich running for an engine, and will also cause mileage and performance problems despite what you might think .