JDM h22 Type-SH swap. Bad gas mileage.
 

I had an engine swap done on my 98 Honda Prelude Type-SH with a JDM h22 Type-SH engine. Originally, my mechanic wanted to use the usdm ecu. After the swap, he kept getting misfire codes (P0399, Misfire on all cylinders). He went through a lot trying to fix it (He used jdm dist, checked injectors, timing, and everything he could think of when he was trying to figure out the misfire. We think the crank position sensor near the oil pump is the problem). I asked him to put the jdm ecu in there to see if codes came up and they didn't, so that's what we put in there.

The engine runs great. However, I am getting bad gas mileage. Worse than with the previous engine. Me and my mechanic were both thinking it's because of the jdm ecu.

My first question is: When doing a jdm engine swap, do you always want to use the usdm or jdm ecu?
Second question: Does the o2 sensors the usdm ecu communicate with increase the mpg? and in my case, since I am using the jdm ecu, I am getting worse mpg because they ecu doesn't work with them? Is there a difference between the two in what mpg you get?
Third question: Should I attempt to put the usdm ecu back in and try to get it to work without throwing codes? Or should I just try to get better mpg with the jdm ecu, or perhaps tune it?

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

ECUS depends about what engine you have. You pickd one of the hardest engine swap there - with type s you cannot use any other ecu out there exept JDM one because of ATTS (if you change ecu - you lose ATTS)

normal engines without ATTS are much easier since if you dont have correct ecu there - you can get chipped ecu and get tune - problem solved.

something else is wrong there, you dont have "USDM o2 sensors" theyre all the same.

you cannot run type s with usdm ecu since usdm h22 engines are completely different than type s engine - wrong ecu - bad mileage & codes

if you do the swap correctly - you change needed parts and sensors there should be no problem to use JDM ecu so something is not right in your swap there

did any new any parts there or just slapped the engine in? you should always do some rebuilding if you get spare part engine

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

You should only be using the jdm block, literally everything else should be coming from the usdm just to be on the safe side, assuming you had no codes from the original motor before it gave out(for whatever reason).

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

You sound a little confused. Don't you mean USDM ecu? I am using the jdm one now.

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

Not even a few posts in and there's already a disagreement with which one I should use. It seems everyone I ask says either usdm or jdm. Who should I believe?

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

as I said USDM ecu is wrong ecu for you - type s engine is different than usdm h22a4

everybody gets confused when you dont provide us proper info: which sensors are there - usdm or jdm - what did you took from old engine (injectors etc) and what are from JDM engine?

did you new any stuff like ignition parts and so on?

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

I hope the USDM is the wrong ecu to use. However, I got several people telling me otherwise that you want to use usdm on all 5th gen.
I'll have to double check with my mechanic, but I'm pretty sure everything is jdm.

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

What wire harness did you use? Which injectors? How poor is the fuel mileage?

I don't see anywhere in the post saying its a Type S engine. I'm guessing JDM type SH should be pretty close with just a bit more compression, I'm too lazy to look it up.

Normally you would use everything from the USDM engine to keep things simple. Oil pump is the big one since the JDM engines generally don't have the Crank sensor on the timing belt side. If you use everything from the USDM engine, including injectors, throttle body, distributor and possibly intake manifold you should be able to use the USDM ECU. That's also assuming you are using a stock USDM wiring harness. The O2 Sensor should "should" be able to compensate for fuel changes, you should be using premium gas. Generally this is the way so you don't need to monkey around with the key interlock crap from the ECU and don't need to modify the wiring harness. You may have some issues with the tune still. You may want to hook up a wide band to keep an eye on things.(FYI I don't know all of the differences between the JDM and USDM SH engine so it may be somewhat simpler or harder depending on the differences. My experience is always with non-SH engines)

If you use the JDM harness and ECU and don't have any issues with the ECU and Key that should be fine as well. Just leave everything as is on the JDM motor and you should be good to go, that would be the simplest way to do the swap. Smog may be an issue.

If you are mixing JDM and USDM you will have to do some wiring for the Distributor and Crank position sensor, the sensor is on the oil pump for USDM and in the distributor for USDM.

Maybe its something simple like a Vacuum leak, I assume your mechanic has done the basic troubleshooting. Generally what would be suggested is to pull your intake and on the inside of the throttle body is a few holes. Cover them with your finger and the engine should die very quickly. Pretty much as soon as you plug the holes. If it does not die or sputters at really low RPM then you definitely have a vacuum leak. When the throttle body is closed there should be no air getting into the engine, the IACV is ECU controlled and is basically a controlled vacuum leak to keep the engine idling if you cover the holes it wont let air into the engine and it should die almost immediately. If there is no suction that's and issue as well that means the IACV is stuck closed.

If there is not enough vacuum or too much vacuum the engine will have poor fuel mileage, the Map sensor sends the Vacuum readings to the ecu to determine proper fuel maps and I could be wrong but may affect timing as well.

Sounds like you definitely have everything you need to make things work, just a bit of tweaking and you should be good to go.

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

there is no "JDM type SH" only thing which has ATTS in Japan is Type S?

and USDM H22A4 SH is VERY different engine than JDM H22A Type S

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

Interesting.. Well I don't know much about the SH. If its actually a type S then the tune is going to be a big issue with USDM ECU.

Did you buy the complete swap? I see the full swap for $2999, honestly I expected it to be a lot more. My H23avtec ended up costing me about 2500 and that's not a type S.

If you used everything from the JDM motor including harness and ECU you should be fine. My first thought is hook up a wideband and see if your running rich.

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

Ok, type-s then. Yes I got the complete swap. I will ask my mechanic later.

I am so frustrated right now.

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

also always when you get replacement engine its wise to do some rebuilding - call it basic maintenance if you will

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

Can we get back to the OP's original ISSUE please... "Bad fuel economy" !!! This old guy is going to interject some common sense in the discussion if you all here don't mind. IF the JDM engine that the OP had installed in the car is similar in HP output as the H22A4 originally found in the Prelude, the original USDM ECU programming should run the engine fairly well and the fuel economy should therefore be very close to what had been previously experienced with the H22A4. Now, if the new JDM engine is in fact a higher output "Type S" variant, then the stock USDM ECU will essentially run the engine LEAN... and fuel economy will in fact improve in the best case and stay essentially the same at worst. The danger of running an engine in this manner is "Wide Open Throttle" operation... it will still be lean (likely very lean at WOT) and that is harmful to the life of the engine. So, if you install the JDM ECU which came with the swap, one would think that the fuel economy would be similar as to what the OP had experienced with the original H22A4 combination... maybe a 2-3 mpg loss at worst. With this said... the problem is elsewhere.

The OP mentioned random misfires with the H22A4 ECU but not with the JDM ECU... this is because there are NO MISFIRE CODES to register in the JDM programming. So this is not a fix... the JDM ECU is merely masking the problem. My first thoughts would be improper mechanical timing, a bad ECT sensor, a bad IAT sensor, or maybe even a damaged MAP sensor.

So ftr, pull the valve cover, roll the crankshaft to TDC and see if your cam gear markings line up correctly. One cam off just one tooth is enough to cause misfires and loss of power... which requires greater throttle angles and higher fuel usage for normal operation... resulting in poor fuel economy. If the engine is in proper mechanical time, get a scanner that is capable of monitoring live data while the car is running. This may only work with the stock H22A4 ECU... but look for strange values in ECT or IAT... really low (cold) values will be responsible for bad fuel economy. If the MAP sensor is reading low vacuum values, this would also contribute to unnecessary fuel waste... resulting in poor fuel economy. If you aren't prepared to do this testing, discuss it with the shop that installed the engine... maybe even make a print copy of posts that you found useful to help them with diagnosis.

Good luck.

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

Oh, my apologies ftr... I should have also offered answers to the questions that you originally posed,

First Question: If using a stock engine, it is always best to use the ECU designed for that engine if possible.
Second Question: Both the USDM and JDM ECU's will work using your primary O2 sensor to try and maximize fuel efficiency during idle and part throttle operation. The JDM ECU will not recognize the secondary O2 (post cat) sensor, but this is an emissions related component and has no bearing on engine operation.
Third Question: Not an easy answer here. If you are in a state that requires emissions checks, then you will have to use the original USDM ECU to pass smog. Without such requirements, it is likely that the JDM ECU will perform safer and better. For your own peace of mind, I suggest you take the car to the nearest dyno (obviously AFTER the engine has been fully diagnosed and repaired) and make a 3rd gear full power pull using each of your ECU's... and the one that is the safest at WOT would be my choice.

You never were specific in how bad the fuel economy is compared to what you had experienced with the H22A4. Is the loss significant or only a couple-three mpg less ??? Can you contribute the lower fuel economy to your early excitement and spirited driving while enjoying the new engine ???

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

my point: if hes using some old stuff which came with the engine like spark plugs, wires etc - theyre effecting fuel economy
AND IF they didnt clean injectors, egr & other valves - they might be pretty clogged - same effect

when engine sits in warehouse for years and you dont know how it has been driven before you just cannot install it another car and expect that it run well

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

Thank you, JRCivic1 for your response. I feel like your response has been one of the more rational and helpful responses in my current situation. Yes, my JDM h22a Type-S is more powerful (20 more HP)...... Hmm, strange, my mechanic did a compression test when he was troubleshooting and he said he was getting ''surprisingly high readings (240 psi on all cylinders)" I just looked online (maybe my sources are wrong at the moment) and it says the JDM h22a Type-S is 220 ps? that's strange.

Yes, the engine swapped should have more output and that was one of the reasons I decided to go with using the JDM ecu. The idea of using the USDM seemed... weird. However, Some people keep telling me otherwise. Me, being a novice with limited knowledge at the moment, thought the only benefit of using a USDM ecu, would be that you can get your emissions checked. I don't have to have emissions where I live, so I just told my mechanic to just use the jdm one.

With the check engine light code (P0399, all cylinders misfiring)on the USDM ECU. During the almost two weeks of my mechanic trouble shooting, he did the following:
Changed Distributor
cap and rotor
plugs and wires
fuel injectors
cleaned egr
map censor
knock censor
adjusted the valves
compression and leakdown test (240 on all cylinders)
verified timing belt

He was stumped. He said it ran and sounded perfect. Now, after doing some research and talking to him.. we both think it could be the crank position censor at the oil pump. I THINK he did pretty much everything except change the oil pump. We will continue to talk about it as I get more information.

With the gas mileage. I noticed I was going through a tank significantly faster AFTER the swap. I don't have a specific mpg, but I will soon. I got the needle dead center to the middle marker on the fuel level and added 6 gallons. I am going to drive it until it drops the that level again (shifting at 3000 or lower) then calculate my mpg.

As of right now, I think I may keep the JDM ecu (unless someone can convince me otherwise). My concern right now is, the mpg, misfire on the other cpu (which is masked now?), and the fact that my mechanic did not mess with the oil pump and if that is something I am going to have to get fixed.

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

isnt there a small conflict here....?

OFF TOPIC
It depends about swap - like for example using USDM H22A4 ecu is the only way/one of the easiest way to use H23A VTEC or then chipped ecu.

Or then people dont get JDM ecu with their engines so they need to convert their JDM engine to use USDM ecu (thats why you need to change dizzy, oil pump etc)

So with that background people tried to help you out. Like I have said this is little bit different case.

And people from other countries dont have to deal with USDM electrics so their advices are then different also.

that was just mistake, since using that USDM ecu in this JDM engine dont work properly and your mechanic should have known that - now he wasted time





Its the right ecu for this engine. Did you use JDM injectors? Im not 100% sure but there might be some difference in voltage/resistor box or something vs USDM ones. Look into that as well.
And what fuel are you using? There might be difference as well since its JDM ecu there. Like mentioned use premium high octane.

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

Ok, guys. So I got 162 miles from 6 gallons of gas driving very economically shifting lower than at 3000 or lower and driving 60-70 on highway. My average is 27 mpg. If that was eco then regular driving/vtec driving I would get 20mpg?

Since I am using jdm ecu, do I need to make sure I am using jdm oil pump? My mechanic said it would be a lot of labor to get to it.

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

Thats not "bad mileage". Higher side of normal I guess but not that bad

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

Honestly that does not seem horrible to me.

I'm not sure me and JR are on the same page. The new ECU I assume is an OBD2 ECU and should be very similar to the USDM one. I don't see why it would mask the problem. Usually when you do a swap you would go from OBD2 to OBD1 so you can chip and tune but with your Type SH you are extremely limited and had to stick with the OBD2 SH ECU. I'm certainly not an expert on OBD2 SH ecu's so I don't mind being corrected here but I'm thinking that main difference is the tune and not much else.

I am pretty sure the reason you had issues with the USDM ECU is the Crank Sensor, I think you are on the right track with that, Since you used the JDM Harness you needed to use the JDM ECU. You should be able to make the USDM ECU work but honestly the JDM ECU should run it better anyway.

The JDM engine has an EGR right? I'm pretty sure my H23vtec did. You may be ok for smog. Does it have a vtec oil pressure switch? I have read that sometimes visuals are failed because its missing. I swapped mine over when I did my swap.

Getting the car on the Dyno isn't a bad idea but honestly just installing a Wideband will give you piece if mind for more than one pull and may be cheaper. As long as it isn't running rich and your not leaking any fuel I don't see why you would have an issue. Have you run a full tank of gas thru the engine yet? I have been told OBD2 ECU's take some time to learn so you need to put at least 100 miles on the car for things to smooth out. I could google a bit and see if that's a fact but I don't want to.

OIL Pump.
The USDM oil pump has the mount for the Crank position Sensor. The JDM does not.. As far as I am aware that's the only difference. You don't need to swap it unless you want to add a Crank position sensor there. The JDM motor and harness have the sensor inside the distributor so its wired differently. If you planned to move the Sensor it may be easier to use the USDM harness.

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

Yeah I have run a few full tanks. Maybe it was my driving but I think I may do what you said and install a wideband and take it to the dyno. Also, Is it fine that all of the parts are usdm except for the engine and the distributor?

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

27 MPG out of a 5G Prelude is not LOW... it is very average... especially for mixed mileage. Maybe 1 or 2 MPG less than what you might get driving Highway only.

We are, but I don't think you fully understand what OBD-2 means here in the US. A computer for a Honda sold in the Japanese market may very well have plug styles that appear identical to some found in Honda vehicles sold here in the US... lets say a 1998 model. However, the PROGRAMMING requirements are vastly different. The US has the MOST STRINGENT emissions standards of any Country on the planet (You can thank California - CARB - for this), and thus, the ECU programming will have subroutines and codes that are unique to the US market. Misfire codes, specifically P0300, P0301, P0302, P0303 and P0304 do not exist in the JDM programming of the H22A SH ECU. Thus, even if the engine misfires occasionally, the CEL on the dash will not illuminate because the codes are not in the ECU. Emissions requirements in Japan are quite limited... so limited in fact that even today, Honda ECU's from the region have codes stored in their internal library similar to that of a OBD-1 US Honda ECU. No VTEC Pressure switch, no secondary O2 sensor (catalyst efficiency), no misfires, no tank pressure sensor, no purge control flow... just to name a few.

So in short... just because the plugs on the ECU match doesn't mean that the basic function of the ECU does... regardless of what ignition and fuel tables are programmed for the specific engine application.

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

That was my test driving it extremely economical. I will keep doing tests. The misfire problem was almost certainly due to the crank position censor that the USDM ecu is so worried about it. At this point, and after further research, I would rather keep the JDM ecu anyway. However, I still have this question. Is it fine if everything is USDM except the engine and the distributor?

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

Thanks for the info JR. I didn't realize that there were that many differences. Seems like a misfire code would be useful for every ecu but everything doesn't always make sense. haha

I don't see any issues with running everything else USDM. The basic components are all the same. Sounds like its running well so I wouldn't touch it unless you are having issues. Which injectors did you end up using?

But as I said above, if you install a Wide Band and see your running rich or lean you know changes will have to be made. The car can drive really well and feel great and still be on the road for failure due to poor Air fuel. My H23vtec felt awesome and I was going to get it dyno tuned but I decided to install a wideband first. Once I got it installed I found it running super rich. I was able to adjust the tune myself to some degree but watching the air fuel I found that I had some other issues. I would hate to waste 500$ on a tune and find out I had to retune after a few weeks because of a faulty wire.

Wideband and Vacuum gauge are essential to tuning. I also like to always have a oil pressure gauge to keep an eye on engine health and it doesn't hurt to have a temperature gauge so you can communicate engine temps without pointing to 9:00, 11:00 and boom.

Re: JDM h22 Type-SH swap. Bad gas mileage.
 

There are three positioning sensors needed for proper engine function: TDC (Top Dead Center), CKP (Crank Position), and CYP (Cylinder Position). On stock '97+ Preludes, the CYP sensor is located in the distributor and the TDC and CKP sensors are mounted on the oil pump around the crankshaft snout. On the JDM engines, all three sensors are found inside the distributor. Either ECU will run with either sensor package... just as long as you have one combination or the other... not a combination of the two. So, in short... if the USDM was upset with the CKP, the JDM ECU would be too if you were using the same sensor package. Yes, it is fine to run the JDM engine and distributor... AND the JDM ECU.

True that. Misfire codes are a tiny bit helpful for diagnosing engine problems... but the engine can be diagnosed easily and competently without them. You are most welcome. Always happy to help.