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Gt4 Exhaust


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Hi guys, I own a 1990 ST185 import. I recently gave a friend of mine (who happens to be a mechanic) a go who wasnt impressed and said that it wasnt running properly. He thinks that because i have added a straight through 3" exhaust and de-cat to the car, there is not enough back pressure for it to run 100%... would that be right?.. And if so, how would that be overcome cos it sounded a bit weird to me!.. I have no idea about engines, cars etc and should probably stick to modifying skateboards! So if he is full of it could someone please advise me. Thanks.

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front pipe to cat i think thats right has to remain 2.5 inches.

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shouldnt be an issue most people decat st185s

try doing an engine diagnostic check

Interrogating the ECU will hopefully point you in the right direction for your fault. If not, at least you'll know what the ECU is doing and what IT thinks is wrong!

When should I do this?

If you think you have a fault

If the engine check light comes on

Periodically to check for any stored codes

Just to have a poke about and see what it does

So you can mention it at the next GT4 meet and look clever!

How do I find out if I have any error codes?

Turn the ignition key so that the car doesn't start but powers up the instruments. On the right hand side in the engine bay is a connector marked "diagnostic". Open the protective flap. On the inside of the lid is a diagram showing the location of the pins and a letter identifying them e.g. OX - (Lambda sensor). Locate the T and E1 terminals and connect these together with any old piece of wire, or e.g. a paper clip.

Diagnostic connector location, in the same location on the 185 and 205 Inside the 165 diagnostic connector Shorting T & E1 together, 165 diagnostic port shown The engine check light on the dash will flash rhythmically for no errors but will flash a code if the ECU sees a fault condition The CEL looks like this

Note that the ST185 and ST205 designate these 2 terminals as "TE1 and E1"

How do I interpret the error codes?

Once you have bridged the two terminals together look at the orange engine check light on the dashboard on the right hand side of the steering wheel. This light will flash to indicate any error codes. If this flashes regularly then everything is normal as far as the ECU is concerned. If there is a series of flashes or codes then interpret these as follows:

E.g. for code 54 - 5 flashes, small pause, 4 flashes, longer pause, then 5 flashes, small pause, 4 flashes- this repeats...

*.*.*.*.* .. *.*.*.* ..... *.*.*.*.* .. *.*.*.* .....

5 4 5 4

* = Dash light on

. = Dash light off, (a slight pause)

thanks to www.gtfours.co.uk for the information

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if your car was normally aspirated he'd be right but turbo cars need as little back pressure as possible.

what you can end up with if your running a stock turbo and a 3" system from the down pipe back is boost creep, that is the boost will not stay at a set level as the wastgate is of a poor design and the exhaust gasses find it easier to go through the exhaust turbine thus causing overboost. this will make the car lack power until the ignition is switched off.

if this is the problem putting a 2.5" restrictor in the exhaust will help

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Thanks for the ideas folks. I had an attachment with the exhaust which is to be placed into to the tail pipe to narrow it, im guessing that is the 2.5" restrictor in question. I will pop that in and secure it and see how we go. Failing that, would it be at all possible to remap it and get everything configured correctly?

Please dont laugh if im miles off :blushing:

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you cant remap the std ecu im afraid.

have you got any fault codes from it?

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