4G63 DOHC wont rev

tj-xr5t · Post by **tj-xr5t** » Thu May 12, 2011 4:41 am

Hey guys,

I've just finished shoehorning a 4G63 DOHC N/A in to a 1975 Mitsubishi Galant Hardtop and I'm having a little bit of trouble getting it running.

I'll post it in the members section when I get a change but in the mean time, heres the link to my build thread

First off, I've used a Hyundai G4CP motor (but if anyone asks I tell em its a 63

) and utilised all the original running gear like the ECU and the manifold and throttle body plus the airbox and airflow meter. Recycled everything I could. It's freshly rebuilt and the wiring was done by a professional auto electrician after i'd stripped out and shortened the loom to suit the car.

Now it's all bolted in and it does start and idle perfectly fine but when you open the throttle it used to just "hunt" Heres a video: http://www.youtube.com/watch?v=IObn2qvQEzA
but now just as soon as you crack the throttle open it misfires, sputters and if you try and open it right up it pops back through the inlet manifold.
heres another vid:http://www.youtube.com/watch?v=cZE1ZH-EIDc
Excuse the rattley lifters. They're getting better.... i hope.

I've set the base timing at the zero mark but it doesn't advance when you try and rev it (it does actually rev a little, but shortly after dies) the timing actually gets pulled back, quite a long way too.

Just tonight I checked the TPS as per the service manuals instructions I.E. checking the resistance on the ground and signal wires while slowly opening the throttle body, and that works fine.
I did a continuity check on the wiring from the TPS back to the ECU to see if there's a break in the wiring and its OK.

Like I said, it idles fine and adjusts the throttle on its own as it should when it starts but it just wont rev at all.

Any suggestions on what it might be that's causing the issue?

kurb_appeal · Post by **kurb_appeal** » Thu May 12, 2011 3:17 pm

I know this sounds sill but check your firing order of the wires from the coil pack to the engine. Since 1+4 and 2+3 fire together it may run fine at an idle if they arent far off in order. I have done this a few times by not paying close attention when hooking up my wires. Get them straightened out and you should be good to go.

jeffball610 · Post by **jeffball610** » Thu May 12, 2011 3:38 pm

My first guess is the temperature sensor. The vehicle will go into limp mode if it doesn't find that sensor.
Next would be the MAS. Make sure you are getting a signal from all of the sensors in there.
Next would be timing. Make sure you set it correctly by grounding out the timing adjustment ground. Check VFAQ.com if you don't know what any of this means. The ECU needs you to tell it you're making adjustments otherwise it will make it's own adjustments no matter what you do. This is also true for setting the idle screw.
After all of that checks out (and assuming you have no CELs) then I would start hunting down components that may not be working. It took me almost two days to figure out that the wiring to my injectors was bad. I was completely confused and thought I had a bad injector. Make sure everything is firing correctly before swapping parts out that seem bad.

tj-xr5t · Post by **tj-xr5t** » Thu May 12, 2011 6:38 pm

Thanks guys. I'll follow these points up when I get home from work tonight. I think I know where that plug to ground the timing is, I found a plug in the engine loom that was a single wire with a capped 2pin plug that as far as I could tell from my diagrams (which were poor at best) was for "diagnostics" it was blue with a red trace but I've discovered that the colours of the wiring doesn't always line up between Hyundai and Mitsubishi.

I'll report the results after I give it a go.

tj-xr5t · Post by **tj-xr5t** » Fri May 13, 2011 4:10 am

No dice, although my timing is now correct as per the specifications.

I'm going to look into the MAF next, I did actually pull it apart trying to see if there was a way to modify it (i did notice a few ideas over on VFAQ) but decided against it at the time and put it back together.
Are there any methods at all for testing it a similar manner to the way you test the TPS?

jeffball610 · Post by **jeffball610** » Fri May 13, 2011 4:37 pm

If you don't already have a Palm or other device for datalogging, then get one immediately. This is an invaluable tool. You can read every engine parameter the ECU sees with a simple device. You can also do the same thing with a laptop, although not quite as portable.
Check out:

http://mmcdlogger.sourceforge.net/

tj-xr5t · Post by **tj-xr5t** » Sat May 14, 2011 3:42 am

The palm reader looks like a good idea, if a little fiddly, but I'll look into it soon.

Good new however, I found the problem.
There was a break in the wire for the closed throttle switch which was most likely shorting out telling the ecu that the TB was going open-closed-open-closed etc hence the odd behaviour in the first video.

It's now moving about the garage under its own power for the first time since the build started nearly 18 months ago. All that's left is to put the grille and the bonnet back on, finish adjusting the new rear brakes and then its on the road terrorising Honda Civics!

Thanks for your help!