Q&A Tech­ni­cal is­sues solved

Michael Clev­er­ley of Clev­er­ley Re­paired Cars, ex­pert on all things MX-5, an­swers your ques­tions

Total MX-5 - - CONTENTS - Send your ques­tions to cr­cmx5@gmail.com

Elec­tri­cal woes abound, and a reader wants a cheap power up­grade solution for his mk3

JUDDERY DECK

QI have a mk3 coupe with the fold­ing metal roof. It all works OK, but re­cently the rear deck has started to jud­der badly when clos­ing. I have tried oil­ing it, but it’s no bet­ter: any sug­ges­tions?

AThis is a prob­lem we’ve seen a cou­ple of times now and it’s been quite easy to cure. You need to work out which side of the rear panel is jud­der­ing by get­ting an as­sis­tant to open and close it while you have a look.

Next, undo the two 10mm headed nuts hold­ing the metal deck panel to the mo­tor unit. Note the height shim po­si­tions and us­ing a marker pen draw around the mount­ing point so you can re­fit the panel in the same po­si­tion. I usu­ally undo only one side and sup­port the panel with a rolled up towel or sim­i­lar, but you could re­move it com­pletely for bet­ter ac­cess.

Now you can re­move the mo­tor and gear as­sem­bly; it looks a bit like an elec­tric win­dow lifter. It’s held in place by two 12mm-headed nuts and a plas­tic trim is clipped to it. Push the trim to one side and then lift out the unit, dis­con­nect­ing the two mul­ti­plugs as you do so.

On the bench you’ll see that the mo­tor is bolted to the gear frame with three screws: these come loose al­low­ing the mo­tor’s gear to move out of mesh with the lifting gear. It’s this loose­ness that causes the jud­der. If you pull the mo­tor gear in tight to the main gear and tighten the mount­ing screws firmly, on re­assem­bly you should find the fault is cured. It’s a good idea to clear the drains while you are work­ing in that area.

BAT­TERY BOO-BOO

QI left the lights on on my mk1 MX-5 last night and flat­tened the bat­tery. I tried to jump start the car and now noth­ing hap­pens, no lights or any­thing. Please help.

AI’ve had this be­fore and think the prob­lem will be sim­ple to fix. The bat­tery ter­mi­nals in the boot of a mk1 are very hard to get jump leads con­nected to and I won­der if you briefly re­versed the po­lar­ity or shorted the bat­tery ter­mi­nals. This will blow the 80

amp main fuse lo­cated in the fuse­box on the driver’s side of the en­gine bay. It’s easy to see if the fuse has blown by look­ing through the clear plas­tic lid of the fuse. It’s not so sim­ple to re­place the fuse, how­ever. You must undo the fuse­box (dis­con­nect the bat­tery first) and lift it up a lit­tle. The fuse bolts in with two short 10mm headed bolts. One is cov­ered by a plas­tic flap that you need to un­clip. Bolt in a new fuse and re­fit the fuse­box. Charge up the bat­tery and re-con­nect it.

When jump-start­ing I tend to con­nect the pos­i­tive jump-lead di­rectly to the pos­i­tive bat­tery ter­mi­nal and then con­nect the neg­a­tive jump lead to the bat­tery mount­ing clamp bracket – it’s a lot eas­ier to ac­cess than the neg­a­tive bat­tery ter­mi­nal. With a flat bat­tery I would jump-start the car, leave the en­gine run­ning with the jump starter still con­nected for a few min­utes to let the bat­tery charge a lit­tle, then re­move the leads. This re­duces the power surge when you take the jump­start off and lessens the risk of dam­ag­ing the elec­tron­ics.

LIGHT RE­LIEF

QMy mk2.5’s en­gine light has been com­ing on, some­times per­ma­nently, and other times it comes and goes. Do you have any thoughts on what might be caus­ing this?

AThis model has an EOBD di­ag­nos­tic port mounted to the right of the steer­ing col­umn, mak­ing elec­tronic fault find­ing eas­ier than early cars that use blink codes. Of­ten on plug­ging in we see code PO420 – ‘cat­a­lyst sys­tem op­er­at­ing be­low ef­fi­ciency’.

The next step is to run the car up to op­er­at­ing tem­per­a­ture and measure the ex­haust emis­sions; if the lambda (oxy­gen con­tent) is around one and the car­bon monox­ide near zero, the cat­alytic con­ver­tor is func­tion­ing cor­rectly.

In this in­stance re­plac­ing the rear­most lambda sen­sor of the two fit­ted to the ex­haust sys­tem and clear­ing the fault codes will cure the prob­lem.

If the emis­sions are high then you need to con­sider re­plac­ing the cat­alytic con­ver­tor with the best qual­ity part you can af­ford. Cheap cats don’t last!

You also need to con­sider why the cat has failed. Some­times it’s sim­ply old or dam­aged through be­ing hit. Air leaks up­stream of the front lambda sen­sor, ig­ni­tion mis­fire or bad fuel can all dam­age the cat. If you don’t find the cause it’s likely your car will be fine for a lim­ited time and the fault will then re­cur.

POWER HUN­GRY

QIs there any way I can get more power out of my mk3 with­out hav­ing to spend an ab­so­lute for­tune?

AWith mod­ern cars not fit­ted with tur­bocharg­ers, big power gains aren’t that easy. The man­u­fac­tur­ers have al­ready pro­duced very ef­fi­cient de­signs that are dif­fi­cult to im­prove on.

What we do with the mk3 as a first stage is fit a four-in-toone ex­haust man­i­fold such as the Rac­ing Beat or IL Mo­tor­sport items. This deletes the front cat, in­creases ef­fi­ciency a lit­tle and looks great un­der the bon­net. The sec­ond cat still al­lows an easy emis­sions pass at MOT time.

You have to in­stall the front lambda sen­sor into the new man­i­fold af­ter ex­tend­ing the wires a lit­tle (they will stretch but we pre­fer to route the wires bet­ter), and weld a new rear sen­sor mount just be­hind the re­main­ing cat­alytic con­ver­tor.

Next we fit a K&N air-fil­ter and then get our lo­cal dyno guys (Hy­brid Tune) to remap the ECU. On 2.0-litre cars you end up with about 180bhp at the fly­wheel and around 150bhp with 1.8s, plus a torque in­crease through­out the rev range.

Mk3 fold­ing metal roof deck

Above: mk3’s fold­ing metal roof lifting gear re­moved from the car and the mo­tor un­screwed from the lifting mech­a­nism – the two items need to be screwed back to­gether very tightly and the jud­der­ing should stop

Top: mk2’s EOBD lo­ca­tion, above fuse­box. Above: rear­most lambda sen­sor – stick­ing up from the pipe – can fail and be the cause of en­gine warn­ing lights. Or, the cat­a­lyst may need re­plac­ing…

Try­ing to get the neg­a­tive (black) jump-lead onto its re­spec­tive bat­tery ter­mi­nal in a mk1 is a night­mare: a mis­take can blow the 80-amp fuse. Us­ing the bat­tery’s clamp is less po­ten­tially haz­ardous

A four-into-one ex­haust man­i­fold gives a lit­tle more oomph to a mk3

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