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86 505 STI XN6 Restoration


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Recently started messing with this car around 3 months ago. The engine will start very easily, but dies after 2-6 seconds. After around 30 minutes of starting and stalling, the car will run for 10-20 seconds which i think is due to the engine warming up. I have replaced a few parts, and checked the common stuff, but I am no expert on cars, especially mechanical injected ones, but am willing to do whatever it takes to get it running. The car also backfires a large amount (sometimes it can backfire 10-15 times within a few seconds). I took off the rubber boot above oil bath, it has no cracks, and is put on properly. Interestingly the car seems to be running off the cold start injector, because when I disable the cold start injector, the car wont even start or even catch for a second. After trying to start the car for a while you can occasionally use throttle to keep it going, but it will die eventually. Really want this car fixed, I have replacement interior panels for all of it, so any help is much appreciated!

Parts I have replaced: Fuel pump, fuel filter, fuel tank. Oil changed, fluids topped up.

Parts I have tested to be working correctly: Fuel pump relay, Air meter plate under the air boot. Also there is spark to plug wires, not sure if its timed right or not (idk how to check that). 

A couple things that concern me: The black rubber grommets that connect the intake barrel to the 4 intake runners are very loose (backfire sometimes bursts from there, sometimes shooting gasoline out). The back window has been busted for 2 years ever since a tree fell on it (yes an entire tree, but somehow only small dents on the car...) anyway.. the tree fell on the car and now rain can easily get inside the car (only recently I put a tarp over it.) Should I pull the computer out? not sure where it is. Maybe someone here will have an idea to help me, this car stumping me, and my dad. oh and the in-tank fuel pump does not work, but I think somebody said the car can idle fine without it.

        - Jayden

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Have you tried spraying fuel or propane in the intake, to see are you losing spark or fuel, i've had something similar happened, someone had stolen my gasoline and fill the tank with water, how the car run i don't know but it will start up for few seconds and die, i sprayed some brake cleaner in the intake and seen i can keep the engine running, that got me checking the fuel pump that was an intake pump, when i took the assembly out, it was clear to me what happened, the fuel / water line was very visible.

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I dont think I have tried spraying fuel in the intake. This is probably a dumb question but: how does spraying fuel tell me that it has bad spark/fuel? i am big noob.

 

also stealing gasoline?? what I never heard that one before hahaha

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Well here gasoline is 6$ in the summer comes up to 8$ a gallon, monthly income is probably 10-20% from the US income, so gasoline is stolen often, more in the olden days but it happens till today. Pouring liquid gasoline in the intake is not advised, any back fire it will blow the intake. Starting fluid or propane is more safe because its vapor, in the pass i've stuck everything from camping stove, to map gas torch in intakes, but quickest i've found is to have two people one inside the car cranking and applying throttle and small amounts of brake clean, if the engine runs more time then without it, you missing fuel.

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8$ holy cow. Its less than 2$ right now here in the US. Might try brake clean in intake, takes about 1-2 weeks to get my dad outside to test stuff... he also dislikes putting stuff into intake. Also if im putting something into intake I will be making a vaccum leak most likely right? would that invalidate the test?

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Hey Jayden, 

Get some black wide zip ties and synch those boots down nice and tight.  Big vacuum leaks can cause similar issues to what you describe. 
 

Using brake kleen on a CIS car is a little tough, but you can usually use one of the vacuum ports to spray it into the intake without causing any issues.

You’re sure the Tachymetric relay is working?  Quick bypass for the relay is to just give 12v power directly to the fuel pump.  Tachymetric relay needs to see the engine is running and then it continues to power the fuel pump. Common issue on the Xn6 cars.

You should also see if Jon has a timing light, or see if you can pick one up.  Would be good to make sure it’s timing correctly.  With practice you can time but ear once it’s running - but they’re invaluable for testing.

Lastly - any chance the firing order got messed up?

Rabin

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Hey Rabin,

The Tachymetric relay im pretty confident in working, I can hear it click when I prime fuel pump, and when engine dies after 2-6 seconds I hear it click, and hear fuel pump turn off. Though when I do measure voltage at the pump its usually only 9-10 volts, which should be normal I think? not too sure about that

As for firing order, I did check that - it was correct. Not sure if its normal, but the plug wires are kinda loose

I think my next step will be using timing light, and putting brake cleaner in the intake. Thanks for help everyone!

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Jay, check the wires on the external fuel pump, i've seen dealership replace a fuel pump and the car won't start, after 3 weeks of diagnosis turn out the tech who replace the pump install the wires backwards, - to the positive and + to the negative, the fuel pump buzzes but doesn't pump any fuel, it's always the simple staff that gets you. I usually spray brake cleaner into throttle body, A buddy of my recently got R32 with RB26 half cut, he tried to get it going with no luck i went over spray some carb cleaner, it fired up took the fuel injectors off and they wore gunked up beyond recognition, ultrasonic cleaning and the engine is running like a champ. Parts for those RB engines are stupid expensive

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Will do Goce, thanks. Guess there is a good chance those fuel injectors are filled with gunk, after sitting for 15+ years, and was not prepared at all to sit for that long. (I gotta finish my online school classes tho haha...  I wanna work on the peugeot so badly lmao)

Edit: now that I think about it, I had replaced the fuel tank due to very large amount of rust, perhaps the rust made it way to the injectors and clogged them?

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1 hour ago, Jayden M said:

(I gotta finish my online school classes tho haha...  I wanna work on the peugeot so badly lmao)

Haha, tell about it, i got to teach those classes, and the students have 101 excuses what they'll be doing instead of learning online.

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I teach: Math, physics, informatics in 4 elementary schools in two languages. Yeah kids love me and hate me when i give them a lot of homework, haha.

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Hahahaha.

About the fuel injectors, that car has a weird injection system, do you/anyone know how I could test/check the injectors - besides taking them out and seeing if they spray gas?

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Spray brake clean in the throttle body, see if it will keep running, then check fuel pressure, check injector pulse if all are good then there is nothing else just the injectors.

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How do i check fuel pressure?, I dont think the car has a schrader valve. im noob :D

 

Edit: I think I just stick something into fuel line somewhere like a T shaped brass connector, and hook up gauge. What is good pressure on that car? (i dont have service manual)

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Brass T piece, and a pressure gauge, couple pieces of hose, couple of clamps, remove the hose of the fuel rail, T in a pressure gauge, activate the pump and check the pressure.

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That is the 505 turbo with the N9T engine, which did have normal style bosch injectors, but the XN6 engine thats in the STI has mechanical injection, I can shoot you a picture after my class if you'd like.

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Yeah that's good old K-Jetronic, on those i would trace the fuel line that is coming from the fuel pump, and test pressure where it enters. looks very easy to take off the intake hose, only one hose clamp and you have access to the throttle body. Check first if it will run on brake cleaner, then we will troubleshoot further.

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The tachymetric relay provides 12V to pump to start, but then needs to see ignition signal (tach) to keep power going otherwise it kills power.  Basically a fuel cut device in case of accident if the engine stops running the pump turns off.

12V direct to the pump bypasses this since it fires and dies.  
 

With CIS, the injectors spray more as the air plate moves up or down.  If you pull them you should be able to put them in jars and check spray/flow by moving the air plate.

Google CIS troubleshooting - Volvo and VW used the same system and there should be some good guides for troubleshooting it.

The fact it runs and dies still points to the tachymetric relay until you can exclude it.

Rabin

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