Recently did the 784 fuel injector upgrade, all results were as expected -- better power, smoother idle, except my mileage is horrible...dropped 7 mpg!

No leaks that I can see, what could be the problem?

Update** there's a strong smell of gas now in the jeep, I wonder if one of the injectors is not functioning properly, there is a sound coming from the 4th injector like a shhhh-ing sound...i wonder if it's not spraying correctly

 

There's usually a sacrificial cost for more power... in this case fuel. I don't know the exact drop, but everyone of my friends that has done an injector upgrade on their XJ's, fuel economy always got marginally worse afterwards. So it could just be par for the course.

 

interesting, I was under the impression it was more likely to improve mileage than power, but it seems I’m experiencing the opposite. Truth be told, I’m in stop and go NYC traffic and probably driving a little more aggressively than before now that there is a bit more on tap, but still I wasn’t expecting such a huge drop. Thank you

 

If it helps at all, I saw absolutely no difference in gas mileage when I did my 4 hole swap. It was a consistent 16 mpg on my weekly commute before and after. And yes, that is with wonderful CA traffic.

Did you get a cheap set of injectors off Ebay or a quality rebuilt set?

 

Hmm, I'll have to keep an eye on it, the difference between the average and the immediate mpg seems too different, I'll try a reset and see if I get different results now that the pcm has learned the injectors

I did get them off of Ebay, haha, but from a shop in MA who does a full write up and measures, tests, ultrasonic cleans, etc. each injector, so hopefully they are quality injectors..

 

Trust nobody from MA!!!!!!!!!

 

The power benefit from the injector swap is from better utilization of the fuel because it is more atomized. This should result in an improvement in fuel economy. If your friends are getting worse mileage, they did something wrong. Period. It might be as simple as enjoying the improved throttle response a bit too much, or it might be a vacuum leak at one of the injector seals. Or many other things.


7 MPG is in "something is very, very wrong" territory. There is a problem that needs to be solved.


Carabinerx, two questions for you:

1. What was your mileage before teh swap?
2. How are you calculating your mileage?

 

@BlueRidgeMark to be honest I never really looked before hand, but I remember once seeing 17.5 as my average on the overhead dispakay. Lately it’s been between a 10-12mpg average, again using the over head display. My driving is a little different, and so is my route (way more stop and go), but I feel like I can watch the fuel needle dropping. With it running I can’t seem to notice any issues, but I’ll try refitting the rail and injectors Incase it’s not seating well...

 

I wonder if it's the computer, not using the average mpg monitor, but the immediate(?) one, I'm getting great mileage -- almost 40 on the highway

 

The way the mpg monitor calculates its info is a bit stupid. It is based off factory injector specs and the base fuel map. It does not take in to consideration your long term fuel trims. So if you switched injectors and your long term trim is now off 10%, you mpg calculator will be too, most of the time way more off. For the display to even be close accurate, long term fuel trims would have to be at 0%, which will never happen.

 

Yeah, those displays are interesting, but don't take them too seriously. We should all be calculating our MPG the old fashioned way: Miles driving / gallons pumps. No "miles between fillups", no overhead displays. There only one right way to do it.

I keep my mileage records on my phone in Acar. As a telecom engineer, I have seen a lot of different software over the years, and this is Just Right. They did everything right. It just works.

If you are an Applehead, sorry 'bout that. You are on your own!

 

I read somewhere that an injector can get "stuck open" and keep spraying fuel which could lead to fuel getting in the oil which is definitely happening here, plus a strong smell under heavy acceleration or quick deceleration. There's an audible shhhh sound coming from around the 4th injector...any know about this kinda thing?

 

Was it New England Injectors? They sell refurbished injectors on eBay. They have something like a 2 year warranty. The guys there are super helpful and respond quick. I purchased mine from there just based of the quality of replies I got from them. Granted I haven't gotten mine in the mail yet, but I'm positive if you got them from there they will help you to correct the problem.

 

Fuelio is also a great app. Not only does it keep track of gas mileage, but also all your maintenance and insurance and just about any other expence. Then come end of the year you can see exactly what you spent on you xj each year. Kind of amazing to see whi much it does cost to keep your jeep in tip top shape

 

It was, they are actually working with me now, going to try unplugging them one at a time to see if there is a noticeable difference in the engine, then maybe replacing the one (their suggestion).