4 replies to this topic

[chilly]

Bought a 92 SPi non-runner (head gasket failure) last year and have since been bringing it back to life/refurbishing it. The car starts fine and idles at around 1000 - 1100 rpm when cold. After around 10 mins, the engine starts to struggle and idle rough (500 - 600 rpm). During the rebuild, the following was replaced/ added: -

 

Rebuilt cylinder head

New plugs and leads

New rad

New thermostat and housing (82 degree)

New alternator (70 Amp ... possibly the issue)

New waterpump

New belt

Replaced all hoses with silicone

Replaced all vacuum hoses with silicone

Replaced coolant sensor, air inlet sensor, fuel trap etc

Tappets set as per Haynes

New oil and filter

New air filter

New coil

 

Hooked up to Rover MEMS and no faults found.

 

So i'm thinking the usual vacuum and sensor issues aren't the problem (although I didn't replace the o2 sensor). I'm wondering if the alternator is causing the engine revs to drop due to it's revolution resistance. I don't need a 70 amp alternator and only got it as it was on sale. Can I simply increase the idle speed using the Rover MEMS or do I need to look at the o2 sensor?

 

Any help appreciated. Thanks.

[hunterg30]

Thought the spi thermostat should be 88 . Have you checked how many steps the stepper motor is but you might not be able to do this if not up to correct temp also there's a pinned section on here on how to check the spi wrote by Sprocket

Edited by hunterg30, 23 February 2021 - 08:14 PM.

[chilly]

Checked the pinned topic but ruled a lot of it out as most of the troublesome items have been replaced. Stepper motor is a good shout though thanks. Replaced the thermostat with the one that was in originally (rightly or wrongly). Will get an 88 and see if it makes any difference.

[genpop]

No faults by the diagnostics doesn`t state that all is ok.The diagnostics can only show four defined faults.Better for diagnosing is the log-file,you should publish it here!

[humph]

I've had similar problems twice before, this and high revs.  In my case the issue was the O2 sensor, or in one case the wiring too it. These were intermittent problems for me so tracking them down, even with a code reader, was a pain.  The engine bay loom runs behind the throttle body and can rub through so check for breaks.  The loom on these cars are old not and brittle.  The O2 has wrecked the coolant temp sensor at the same time on mine.

 

Sounds like you've made a good start with diagnosis but do the cheap things first, wiring checks etc. Otherwise you could be thowing good money at expensive sensors.