What Dictates A/F Ratio?

BMCC · Post by **BMCC** » Fri Aug 09, 2013 1:23 pm

It will on the 5th Gen don't know about the 4th. Also it might have to be well out to put on the check light.

Post by **Merlin** » Fri Aug 09, 2013 1:29 pm

I will check the resistance of the suspected fault one and a known good one and report back.

Just checked the manual a bit more and a code will be thrown if the temp sensor is faulty, but like you say it might need to be way out

judderod · Post by **judderod** » Fri Aug 09, 2013 2:31 pm

Did it pass the emissions test?

Post by **Merlin** » Fri Aug 09, 2013 2:35 pm

Yes, a non-CAT one. I didn't see the emissions report though.

Post by **Merlin** » Fri Aug 09, 2013 2:50 pm

After scanning the 5th gen manual for ideas I came across this. Even though this is for an OBDII engine it might give me a few pointers.

DTC P0172 System too rich:

Fuel pressure regulator clogged, stuck open
Fuel return pipr clogged
Fuel injector leaking
Gasoline at wrong spec
O2 sensor deteriorated
EGR system insufficient flow
EVAP purge control solenoid valve leaking or stuck open
Valve clearances

I think the vacuum hoses for EVAP, EGR, and fuel pressure regulator are worth a check too to see if any are leaking.

BMCC · Post by **BMCC** » Fri Aug 09, 2013 3:00 pm

Just remember when checking the ECT that it is not just about the correct resistance but how quickly it can change resistance. I reckon the problem in my Pulsar could have been that the ECT was just slow in changing resistance.
I put my old ECT and new ECT in water I had just boiled with a thermometer and measured the resistance. All good, but remember your ECU is reading volts not resistance, doing a static test is not really the same IMO but give it a go by all means, just don't be suprised if you see no difference between the two ECTS.

Post by **Merlin** » Fri Aug 09, 2013 3:03 pm

OK thanks. Will probably just swap them over to be sure.

Also quotes from page 11-152 of the 4th gen service manual:

Service manual wrote:
Ignition Timing Control
The ECM (Engine Control Module) contains memories for basic ignition timing at various engine speeds and manifold air flow rates. Ignition timing is also adjusted for engine coolant temperature.

Service manual wrote:
Other Control Functions
When the engine is started, the ECM provides a rich mixture by increasing fuel injector duration

Confused · Post by **Confused** » Fri Aug 09, 2013 3:14 pm

Yup, cold start enrichment. Standard feature on any ECU. Same as a choke on a carb.

ECT sensor is probably the best place to start, the one for my Anglia/Legnum is about £7.

Edd · Post by **Edd** » Fri Aug 09, 2013 3:41 pm

If the ECU thinks the car is cold surly VTEC won't work?

Post by **Merlin** » Fri Aug 09, 2013 3:45 pm

Good point. VTEC will engage once the coolant temp is at 60C. Now I need to find out at what temp cold start enrichment stops.