Random engine cut out - please help

[RallyRS]

Hi,

Its been a long time since my last post. My 1989 legacy RS rally car has been running great.... until recently. I have a problem with a random engine cut out, I think it is electrical but I guess it could be fuel. Anyways, the cut out seems to happen at any RPM but it always when the engine is put under load. I can take off very slowly and it is OK, but if try to push it no power until I come off throttle.

Its difficult to know where to start looking. I had planned to check the fuel pressures as pressure regulator could be faulty. I few events back the car took a big hit to the front left, maybe something electrical in this area is causing the problem?? Also, it seems the problem is allot worse in the wet.

Recent changes to the engine are a set of tuned length extractors. I also replaced the sparkplugs in a hope to fix the problem, but that didn't work, the new plugs are NGK Iriway 9's.

Basic engine info. 1998 WRX STI engine, forged pistons, VF28 turbo, parallel fuel rails, adjustable rising rate fuel pressure regulation, 2L surge tank, dual 500HP walbro fuel pumps, POSSUM LINK ecu, twin turbo inlet manifold, standard legacy water-to-air intercooler.

Any ideas what problem could be? Any help would be great thanks!

[Legacy777]

Well if the wiring is similar to the US models, the engine harness runs along that front left corner (passenger side of the car for NZ). Maybe something got pinched or boogered up.

This is assuming you didn't redo the wiring.

Are you still running MAF based or have you changed to MAP based with the LINK?

[RallyRS]

Hello. Thanks for reply. I've had a good look over the engine harness and can't find any visible damage to the wires. I'm using the MAP setup with the LINK.

Since my last post I have checked the fuel pressure and this seems fine. The problem is still happening and I need it fixed by the end of the month for the next event. I'm currently leading the championship with my old Legacy against many new subarus and mitsi's, I don't want to lose it because of this problem.

I plan to try replacing the coils (although I had them tested and they tested fine), changing the ignition control module (which I'm told is on the right hand strut), and also some ignition relay under the dash. I have also brought LINK and Innovate tunning gear encase there is a tuning problem (this hasn't arrived yet).

Hopefully something works to fix the problem.

[Legacy777]

What ignition setup are you running? You mentioned the ignition control module.....is there a separate ignition tuning/setup or is the LINK controling it?

[kimokalihi]

I was having an intermittent problem like this as well getting on it but it seemed to mainly do it when the car wasn't warmed up all the way. I would get into boost and it would start cutting out and jerking as low as 10psi and it would keep building pressure and jerking all the way up to 16lbs of boost where my manual boost controller was set at. It would also do it when I downshifted and got on the throttle even if it was warmed up. Then I blew the piston rings in cylinder #2 and it appears to only have detonation in that cylinder. I'm stumped. I wonder if it's the same problem you're having?

[RallyRS]

Legacy777 - the ignition control module is a standard part that the LINK controls. I'm not that knowledgable on automotive stuff, it may not be called an ignition control module.

kimokalihi - I don't think it is a mechanical problem.

Some more news over the weekend as well. I replaced the ignition control module and ignition relay, but it didn't help. I then connected my laptop to the LINK ecu and went for a drive. As soon as the funny cut out happened the graphs that were plotting engine sensors went crazy and the laptop was disconnected from the LINK with a message saying something like 'Disconnected from LINK due to errors'. I now think the problem must be in the LINK. I'll have it tested and try to replace. Fingers crossed, next race coming up.

[Legacy777]

Yeah, kind of sounds like it may be the Link. Keep us posted.

[RallyRS]

OK. Another weekend spend on my problem rally car. I replaced the LINK ecu with a standard ecu, it run pretty rough (probably doesn't link the bigger injectors) but anyway it had the same problem as the LINK, so its probably not the LINK that is faulty.

Next, I re-installed the link and setup the PCLink again. See URLs to screenshots below. Notice the blue voltage line on the plot at the bottom of the screenshot. The voltage is dropping at the same time the engine cuts out. Voltage drops from 13V ish to about 6V. I now think this voltage drop is the problem, but as yet I don't know what is causing it.

Does anyone else think this voltage drop would cause the problem? Where should I start looking to fix it?

http://cid-0a436e01f4e4dcf7.photos.live ... oblem2.jpg

http://cid-0a436e01f4e4dcf7.photos.live ... oblem1.jpg

[Legacy777]

Yeah, I'd definitely say the voltage drop is the problem. As for the cause, it could be a loose wire to the ECU or possibly one of the relays.

What I would probably try and do is try and use a voltmeter to test the voltage at some various points, pre-ignition relay, and post ignition relay to see if one of the relays is going bad, or at various spots to try and narrow down where the problem is coming from. If you have a spare analog input to your Link you can run the wire to the input and then log it to compare voltages coming into the Link to where ever you're testing.

[RallyRS]

OK. Spent another whole weekend on the car. My next race is next weekend and the car still has the same problem. I took the car to an auto electrician and they could not find the voltage problem that appeared on the PcLink software. They also could not find any other problems, but they could make the engine cut happen. They thought it was boost cut and try replacing map, but that didn't help. So now I now less money and the same engine problem . I replaced many sensors over the weekend in the hope one was faulty (TDC, cam position, knock, map, boost control, TPS, Idle control) and also replaced the main fuse box and fitted all new fuses. I replaced all earths I could find, no help.

I did remove the boost control thingy completely and run it completely off vaccum, getting about 7-10 psi (normally I get 18-22psi). This seemed to reduce the problem but no fix.

Also. On one of my practice runs I hit the engine cutout many times, very quickly. After this smoke starting coming out under the dash. When I got home I found that it had fried a circuit in the back of the speedo (thing with speed, revs, fuel, etc..) in the top right when looking at the back of speedo. Also, it had fried a electrical box bolted to the bottom of the steering column. After removing both fried units the problem still remained.

I guessing that what ever caused the above things to burn out is also causing my engine cut out.

Anyone got any ideas? I'm running out and so is time until next event

I'm going to try creating a dedicated power wire for the ECU, maybe this might help.

[Legacy777]

That is very weird. I wish I had some additional suggestions for you. Creating the dedicated power lead to the ECU is a good idea. If you still have the issue, I'd say there may be a problem with the ECU.

[RallyRS]

OK. I had a dedicated power and earth lead put in. Picked car up from auto electrician, but couldn't test it because I drove 100m down the road and riped all the teeth off 5th gear!!!!! So this was Wednesday and racing Sunday. Quickly trailered the car home and started pulling out the gearbox. After removing the gearbox found two wires with exposed wire and fixed these (maybe the cause of the electrical problem). Split the box and simply removed 5th, cleaned everything, and re-assembled (working fine but abit dodgy). Got to race on Sunday and had only driven down the driveway to test gears and didn't know if electrical problem was fixed.

Race day. Did the first time run with no problem going easy on car, expect the fire exhauster going off mid run. Posted a slow time but happy to get to end. Next time run I went as quickly as possible, but blow intercooler off mid run and cost me alot of time, set a good time. Last run intercooler blow off again just after start so set a slow time. Ending up getting 4th.

Very happy to get car fixed, it was a panic!!!!

Thank you for everyones help. Next job is to change the intercooler piping as it is costing me alot of time losing boost pressure.

Cheers
Hayden Manson

[Legacy777]

Glad you got it fixed! Wonder what the issue was, the dedicated power & ground leads, or the exposed wires.

About where in the car were the two wires that were exposed?

[RallyRS]

The two wires were exposed behind the intercooler. There is a small container on the back left of the intercooler, it looked like this had rubbed on the wires and caused the wire exposure. The two wires were part of a thick loom, maybe 1" wide. The intercooler shouldn't move this far as on idle they are over than 1" apart. But I am having problems with the intercooler piping coming apart and intercooler coming off mounts, my intercooler must be moving alot while under power.

I think the problem was these wires because the burnt out circuit on the back of speedo was the intercooler light. Maybe this is related, not sure.

Just glad it is fixed!!!!!

[Legacy777]

Yeah...sounds like it definitely could have been those wires.