I've put a z1 in my del sol si because I drive A LOT for work, was figuring I'd be able to get in the 40-45 mpg range with the heavier car attached to it. The problem is that I'm only averaging around 32.

The transmission seems to be from an EK (dx/lx/cx) and I do not presently have the egr connected. Will the egr really make that much of a difference?

I did put in new plugs, fresh oil change (Quaker state full syn) 600 miles ago, running the 175 70 13s from my crx hf at 40psi. Also still running the stock z1 exhaust manifold/converter mated to a hollowed out stock cat shell and stock si exhaust from there back.

Will the egr really make that much of a difference, same with being in 16 valve mode on the interestate at 70 mph? Any help greatly appreciated, I drive over 120 miles a day, so I'll be able to upload performance updates often

 

What ecu? pics

 

^ this and...

Is there a check engine light on?

What kind of driving, city or highway mostly?

And why is the EGR disabled? EGR will increase fuel economy.

You probably know driving at 70mph won't grant you the best mpg the Z1 will make, but you're right it should do better. My heavier '07 with an R18 gets 37+mpg driving 70-75mph, so I would assume you're Del Sol with a Z1 should do better.

 

if this is a stock setup than yes it can benefit from the egr, some or most think the egr is a complete waste of time and gain no performance, well no **** it wasn't meant to be for performance.

 

Or that disabling it will increase power or keep the valves form getting carbon deposits...

 

Along with not using the EGR and the question of what ecu...what about the primary O2 sensor? P07 and wide band?

 

I have a 93 Del Sol Si with a D15Z1. Mine has a p32 (Z6) intake manifold with no egr. 70 mph I'm getting low to mid 40s for MPG. I do have the VX transmission, but I don't think the gearing is that different than a DX. The most important part is that it stays below the VTEC-E (lean burn) change over for MPG, usually around 2500 rpm. If you are getting 32 mpg something aint right.

Questions:
P07 ECU?
No CEL?
Good ignition system -wires, dizzy?
Wide band O2 sensor?

Tires/plugs sound good, mine has an aftermarket 4-2-1 exhaust

 

I have the wires run for the egr, just got in a rush and haven't connected them as my hf trans needs a rebuild after 193k miles. Running the 49 state VX ecu on the wideband sensor. No CEL (doesn't mean something isn't up with a sensor somewhere). I do notice a little bit of oil burn at higher rpms (the few times I get there). From the lag and surge felt during moderate acceleration while cruising, I assume that it is going into lean burn. I might have some free time tomorrow after work to finish hooking up the last 2 wires for the egr circuit to be complete. And will be keeping speeds below 60 in 5th to see what kind of difference can be made with that. Driving conditions have been about 65/35 city/hwy last couple of tanks.

the gearing is a little shorter than my hf (high altitude model with the 3.88 final ) getting 60mph at 2500 in the sol, 63mph at 2500 in the hf

 

oh, and the plugs that came out of the engine (while it was in the hatch) were worn and ashy, white ash over all over everything, electrode not even protruding from the insulator by any real amount, nothing on them seem to signify any major issue other than neglect.

 

If you flipped those two you might see closer to what you're expecting. It's still a low average though.

I have a 96 coupe with a Y7/Z6 with a P2P ecu that I drive back and forth to work. 90% hwy, off the top of my head, 3300 rpm at 80mph and I average 41-42 mpg without trying on hilly terrain.

 

At 70mph with the shorter gearing, you're likely not in lean burn mode, which is where the D15Z1 finds its mpgs. If you can stand to keep it under 2500 rpms for a bit, you could see a jump.

 

If I'm not in lean burn at 3000 rpm, th et e must be something wrong with the motor, it takes the same Second or two after pushing the gas for it to be start accelerating more strongly whether at 2k or 3k.

So far simply not driving like an a**hole, keeping it under 2500 rpm (for the most part) showing 120 miles on about a quarter tank. Let's see if I can continue not driving like a jerk, and keep this ~40 mpg going

And that now 700 mile old oil, is black already, can only guess which $17.00 bs oil changes this poor motor used to get, and how often. Looks I'm also going to be doing some frequent oil changes to get this puppy cleaned out

 

Two conditions must be met for the D15Z1 to get its legendary fuel economy... it must be in lean burn mode, and (therefore) VTEC cannot be engaged. Lean burn is only possible up to 2650 rpms, and VTEC will kick over at 2200-3000 rpms, depending on load. Lean burn will *not* be active with VTEC engaged.

When the VX isn't in lean burn mode, it's really no better than any other D15 in terms of fuel economy.... and it takes a bit of finesse to keep it happy.

Your evidence of ~40mpg is promising!

The hesitation is something to further investigate...

 

Yeah, it's weird, only does it after the throttle stays steady for a little bit, maybe something with the egr not being functional yet (I hope)?

 

That sounds plausible... the ECU might be expecting more instantaneous feedback, based on the EGR system, not realizing it's not going to get it.

 

lean burn only kicks in at a steady foot, if you want to be adventurous you can try a chipped ecu and have it tuned for efficiency. There was a guy on d-series.org who had a d15b 3 stage vtec and was able to lean it out at cruising speeds, no egr or wideband needed.

 

That may be an idea for my next project (i have another z1 motor at the house) Is that the guy that posted hus eg coupe for sale on ecomodder, getting like 60 mpg on stock block and lan evo turbo?

 

Thats a different person. The best part about a chipped ecu is that you dont' need to meet specific measures to lean burn, if its at cruising speed (map, tps) than it will lean it per the tuning if done right. You can really gauge lean burn on the vx ecu with a wideband gauge, which you will have to mount a separate o2 sensor to your headers, requires welding another o2 bunge. Worth it in the end because you can gauge when you are leaning out. Also a boost/vac gauge works as well.

 

The other z1 has an a6* intake on it, so that is the route I'll likely go with that one in the crx. In the mean time, gonna finish hooking the egr up, make sure it's clean and find a vx trans...oh, and obviously NOT drive like an a**hole lol

 

cx trans would also be a good fit. run a little atf in the motor before your next oil change

 

Ok, driving like granny got me to 35mpgs, Since I'm at half a tank at 210 miles again now, after driving 80+ mpg the whole time up and down I-75 (yes, between Toledo and Detroit, that is how you don't get run off the road) I'm guessing that there is something seriously wrong here. If the trans us noisy in neutral with the clutch engaged, would that be one of the bearings on the input shaft?

 

How exactly are you calculating mpg?

If you get the noise with the clutch engaged, and it goes away when you disengage it, that's the input shaft bearing. I've listed to mine for thousands of miles.

 

Ok, cool, I have extras of those, a bunch of extras. Looks like I'm pulling a couple trannies apart sunday. Will report results back monday

 

Gotta find a way to monitor lean burn, and don't go over 3k rpm. Well I'm able to get lean burn above 3k rpm on my 3 stage vtec but I've never confirm that could be done for the vx engine.

 

It shouldn't be that hard. Rig an LED to the VTEC signal. VTEC-E engaged: out of lean burn. VTEC off: in lean burn.

In a good acceleration you can easily feel it drop out of lean burn. It is going from 12 valve operation to 16 valve.

There's a good basic explanation in the VTEC-E section of this page:
Temple of VTEC]

When I first got my car (the Si with the D15Z1) it had a p28 and was in "lean burn" up to a little over 5k rpm. It ran like crap. With a good full tune, I guess you could make it better. If Honda designed it for 2.5k +/- rpm, there's probably a good reason.