SEN­SOR SENSE

Performance Vauxhall - - QUESTIONS & ANSWERS -

@ Morn­ing! I’m in need of some ad­vice and I know that some of your guys are quite at home with the older cars. I’ve just fin­ished build­ing a Chevette hatch which has been built to fast road / track stan­dard so it’s got a five link rear end, discs all round, it’s fully poly bushed and I popped a cage in for good mea­sure. Now, it did have the stan­dard 1256cc en­gine which I toyed with tun­ing up just to re­main true to

PER­FOR­MANCE VAUX­HALL the orig­i­nal de­sign but in my wis­dom, I’ve fit­ted a C20XE and it’s turned out to be a bit of a mis­take. The en­gine is in, it runs and she goes well but only about 3000rpm and on fairly ag­gres­sive throt­tle in­puts. I’ve been through ev­ery­thing – air flow me­ter, coolant temp sen­sor, tim­ing, I even swapped the ECU and the is­sue re­mains. Ap­pre­ci­ate you don’t have the mir­a­cle an­swer but I’m hop­ing one of your guys may have had sim­i­lar prob­lems and could of­fer some ad­vice. Thanks lads. Terry.

ASounds like an in­ter­est­ing, if a lit­tle frus­trat­ing project! We asked our res­i­dent 90’s kid to put down his Game­boy, tie his Air Max and take a look. We don’t have the mir­a­cle an­swer, but if you’ve cov­ered the ba­sics and based on the symp­toms, a couple of com­mon sug­ges­tions were made which were the en­gine speed sen­sors (e.g., cam / hall sen­sor and crank sen­sor) and also the throt­tle po­si­tion sen­sor. The lat­ter of which is al­ways one worth check­ing as it can give all sorts of odd is­sues and would ex­plain why the car is kick­ing into life with the throt­tle at a cer­tain point and above. Check the sen­sor isn’t loose first of all and lis­ten for it click­ing when the throt­tle just starts to open. If in doubt, swap it.

One other sug­ges­tion was the fu­elling. A weak fuel pump or re­stric­tions in the sup­ply could give sim­i­lar is­sues so if you can get one, hook up a fuel pres­sure gauge and go for a drive. With the vac­uum pipe con­nected to the reg­u­la­tor, you should be get­ting around 2.5bar at idle and 3bar un­der load but just dou­ble check what man­age­ment it has as there are very slight dif­fer­ences, but as­sum­ing it’s not miles off then that’s a fairly rea­son­able mea­sure. Also check your coolant tem­per­a­ture read­ings… the sen­sors on en­gines of this era should be viewed as a con­sum­able and one that’s telling lies can cre­ate all man­ner of run­ning is­sues. The only real pain is the car won’t have the abil­ity to dis­play live data so it’s back to the old school sadly – swap bits, get the multi-me­ter out and drink lots of tea whilst suck­ing your teeth and hav­ing a think. Hope you get it sorted.

Old school tun­ing has its pros and cons

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