I recently did an MPFI + Si conversion to my '90 DX, using my '90 Si as the donor. I used the Si motor, trans, mounts, ecu, linkages, axles, knuckle assemblies, front brakes, master cylinder. I kept the DX fusebox since it's the same, and used the DX harness since it was necessary for the MPFI conversion...used the Si harness to hack up for the wiring I needed to extend plugs and such.

Anyways, if the car sits for an extended period of time it has trouble starting. It turns over great, but it takes maybe 5-10 seconds to start up. Once started, it will run/drive beautifully for as long as I need it to. I recently took a 100-ish mile round trip with absolutely no problems.

I'm thinking that maybe the fuel pressure is the problem. Is the car supposed to hold fuel pressure when off? If so, maybe it's bleeding off somewhere when the car is off. If not, maybe the fuel pump isn't doing a good job of priming? Because it eventually starts and runs fine, fuel is the only possible cause that comes to mind. If it were spark or compression I imagine I'd be having other issues, and they would be more intermittent.

This Si drivetrain didn't have that problem when in the Si that I can remember. No CELs after all this work, so I'm assuming it's not my wiring job that's causing the problem especially because the car does start/run/drive fine apart from the delay in starting.

Edit: Not sure if this matters or not, but the little valve assembly on the back/driver corner of the Si intake manifold is not connected to anything. The DX harness had no plugs for this valve assembly, and apparently not all d16a6 motors came with it. I have the male plug for it still on what's left of the Si harness, but I had no idea where the wires go...I think one is BXX on the ECU and the other is maybe a ground? What does this valve assembly do and is it important? Could it have anything to do with my starting hesitation? Photobucket appears to be down, so I can't post my picture of this valve assembly until later.

 

The fuel pump has a valve in the outlet that allows the fuel system to hold pressure. That valve is the #1 for start delays. Swap the pump from your other car and see how it goes. Your pump must not be very good anyway if it takes 5-10 sec to fire.

 

How hard is it to replace the pump? The one on the Si is good as far as I know, but the top cover is all bent out of shape. Can I use the Si pump with the DX cover?

 

Replacing the pump is easy, very basic, just beyond time consuming if you haven't done it before. Or at least if you like doing things the right way the first time and making sure (since you haven't done it before) that you're doing it right.

 

To do the fuel pump it's a mater of draining the tank (or just run it pretty low on fuel). Loosen/ take off filler neck and vent. Unbolting the straps. Lower gas tank being careful to not bend any tubing - take off banjo bolt and lines. Take off all the sending unit nuts and pull it out.

The SI pump can be using in the DX sending unit. You aren't talking about the IACV - are you? B2 I think the pinout location.

 

i imagine he is talking about the ficsv, which is used to inject a small amount of air in extremely cold temperatures. It's not causing your problem i can assure you, and no code would be thrown from it being unplugged, as you have already noticed.

 

Ur injectors are leaking.

Just prime the car 2 or 3 times in the morning.

 

No, it's not the IACV or FITV. Sounds like what D16SiHatch mentioned, and also sounds like it isn't anything to worry about so I'll leave it unhooked.

The main relay on this car has already been reflowed, but I did a thorough inspection on it to make sure they didn't miss anything. Once the car is started it will run and drive like a champ, so whatever is causing the extended start time isn't something necessarily wrong with fuel delivery or else I'd have more intermittent problems...but it does sound fuel pressure related.

As I said earlier, I don't recall the Si having that problem so it may not be anything engine-related, so it may not be the injectors. I didn't re-use the DX filter-to-rail line, I used the Si line for that per the MPFI conversion instructions. As far as the fuel system goes, just the other lines / the pump / the sending unit are the only things on the DX that are being re-used so I imagine if it's a fuel or fuel pressure problem then it's one of those components.

Say it is that little pressure valve in the feed line from the tank(or so I read somewhere), is that something that I can safely ignore since the car is fine once started? Do you think running a batch of gumout injector cleaner might help? If I can avoid replacing the pump, since the pump itself seems fine, that would be nice as I'm tired of working on this damn car haha.

 

Don't waste your time with that garbage - buy some Seafoam and try it out. That stuff works wonders when you run it through the gas/ vacuum/ engine/ and trans (special Seafoam). If the problem persists then check it out.

 

I always heard bad things about seafoam, especially when used on Hondas. I guess there's bad rumors about any treatment you can use...seafoam, gumout, stp, etc. I always opted for gumout because I've used it many times with no issues and it always seemed to work fine, especially the "high mileage" version.

 

Seriously? Seafoam is a money making gimick that cleans out the IM by sending old oil and dust into your running engine. It may net 0.001 mpg increase. The injector cleaner won't FIX anything either. The check valve in the pump is bad, it won't change the way the car runs but is annoying to start up. Just remember, mechanics don't come in little cans or bottles.

 

I figured that check valve may just be gunked up or something, in which case something like Gumout may work. If it's actually bad, ain't no seafom or gumout fixing that ****.

If it's not a sign of the pump actually going bad, then I'll just ignore it and give 'er an extra fuel pump prime before starting if necessary. Don't want to drop the tank on two cars to replace one pump, would rather just wait until I have the need for a walbro.

 

Well if you look on here there is some actual before and after threads with Seafoam. I have seen it myself personally as well. I will agree most injector cleaner is a gimmick especially when it comes to increasing in fuel economy. Who said anything about that though? He wants to clean stuff and it works. Use whatever brand you want - just like penetration oil, some people prefer PB Blaster, WD-40, Liquid Wrench, Kroil, blah blah blah... Use what you want.