Register Login
Shop4Parts - UK's largest online superstore for FIAT and Alfa Romeo parts
Thread Tools Search this Thread
Old 29-06-2008   #1
Join Date: Jun 2008
Posts: 10
Thanks: 0
Trader Rating: 0
Question HT leads, MAP sensor, Lamda sensor & dizzy cap

i have a 2000 UNO 1242cc petrol version central fuel injection with electronic carburettor ( car mfr. FIAT India ). Can someone explain me the terms HT leads, MAP sensor, Lamda sensor & dizzy cap and where they are located..
FIAT Forum Useful Links:
Donate to FF | Buy FF Merchandise | Classifieds | FF Insurance | How-to Guides

ashar786 is offline Reply With Quote Quote 
Old 30-06-2008   #2
Join Date: Jul 2004
Location: Papamoa Beach
Posts: 5,190
Thanks: 315
Trader Rating: 1
alexGS has donated!
New Zealand 
Re: HT leads, MAP sensor, Lamda sensor & dizzy cap

Hi - please try not to double-post (I think you asked this question on your other thread) as it may cause several people to each reply saying the same thing.

To make this easier - could you please attach a photo or two of your engine? Just open the bonnet and snap off a few pics, then attach them to the message (click Go Advanced when you're writing a post, then scroll down and click Manage Attachments).

HT leads (High Tension leads) are the cables that go to the spark plugs. They are soft rubber and have a carbon trace in the middle that conducts the high voltage ("tension"). Over time, the connections and the insulation may break down.

MAP (Manifold Absolute Pressure) sensor is attached by a rubber pipe to the inlet manifold, which is the aluminium casting attached to the back of the cylinder head (it has the injector housing on top). The MAP sensor name is confusing as it actually measures vacuum (engine load) unless your engine is turbocharged.

Lambda sensor is a probe about the size of a spark plug, screwed into the exhaust pipe under the car. It detects the oxygen content of the exhaust gas and was invented by Volvo as the 'lambda sond' sensor. The petrol engine is supposed to run at a specific air-fuel ratio - the lambda sensor voltage switches from low-to-high (and vice versa) at the point of this ideal ratio. It tends to be fitted in conjunction with a catalytic converter, so if you don't have one of those, you probably won't have a lambda sensor.

Dizzy (Distributor) Cap is the hard plastic top of the distributor that has the spark plug HT leads attached to it. The distributor has a rotor that switches the high-voltage to each spark plug lead in turn as the rotor lines up with contacts in the distributor cap. The things to check are the spring-loaded carbon contact in the centre that touches the rotor arm - check it isn't broken off or burned away - and the cap itself must not be cracked, or the cracks will trap moisture and leak away the high voltage.

Most engines made in the last few years do not have a distributor (and therefore, do not have a distributor cap). For example, the FIAT Punto engine (which may be similar to yours) does not have a distributor. Instead, a double-ended ignition coil ("coil pack") is permanently connected to all four spark plugs. The plugs fire in pairs - the one that is needed, plus another plug that doesn't need to fire at that time, which is why the system is called "wasted spark ignition".

Hope this helps as a kind of brief summary of the terms you mentioned plus a couple more

'15 Giulietta 1.4MA, 14 Abarth 500C Esseesse, '08 500 Lounge 1.4 Dualogic, '08 G Spyder, '71 850 Coupe in bits...

Last edited by alexGS; 30-06-2008 at 01:38.
alexGS is offline Reply With Quote Quote 
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump
Similar Threads
Thread Thread Starter Forum Replies Last Post
(T) punto 1.3 multijet MAP sensor & IAT sensor spence Punto (Mk2/2b) 0 14-06-2008 09:25
(T) MAP sensor fault - but it isn't? [throttle body clean] Steely Stilo 21 01-05-2008 08:22
(T) Oil on MAP Sensor & Sensor wires scorched?! DaveX Stilo 6 09-09-2006 08:17
(G) map sensor and lamda sensor dillinger39 Cinquecento / Seicento 0 27-03-2005 20:03
(T) Lamda Sensor - where is it? Pete Lemkin Tipo (Classic) 7 23-04-2004 08:49