Hesitation on acceleration - Ford Zetec engine

Invertigo · 21 Oct 2019 at 12:15

Troubleshooting for the Mrs here, I have a good idea of what I'm looking at but a bit of confirmation wouldn't go a miss.

The car idles fine, but intermittently on acceleration the revs building stutter and hesitate a bit. Now from what I understand this is either an air leak thus letting more air in than the car sees (thus running lean) or an ignition issue.

It's a 09 Fiesta 1.4, so the engine is effectively the old Sigma unit. From what I understand these have MAP sensors rather than MAF, and it's also within the manifold. So that makes me think ignition is more likely, and as such I've ordered new leads and a coil pack to try out.

No codes stored at all, no warning lights etc.

Am I headed the right way here? I checked the resistance over the wires and cylinder 3 seemed a bit intermittent in its reading, but that may just be down to how I was holding the probes etc.

MissChief · 21 Oct 2019 at 12:51

Could be loads of things. Dodgy HT leads, dodgy injector, dodgy spark plug, MAF sensor, lambda sensor on the exhaust making the engine supply incorrect air/fuel ratios. Lambda sensor is usually cheap as chips to replace. Could also be a gunked up throttle body as well.

check hoses too, not just for a leak, some hoses are under vacuum so if they lose structural integrity they collapse in rather than leak and cause problems.

Meaker · 21 Oct 2019 at 23:03

I'd pull the spark plugs and take a look at least.

bainbridge · 21 Oct 2019 at 23:34

Meaker said:
I'd pull the spark plugs and take a look at least.

+1 I'd start there and hopefully the gaps will be massive with worn electrodes.

thezappa · 22 Oct 2019 at 06:54

I had this problem (assuming I’ve understood it correctly), it was the spark plugs.

Meaker · 23 Oct 2019 at 22:12

This is what you don't want them to look like

Invertigo · 24 Oct 2019 at 08:58

From the service history the plugs were changed last year before purchase, so I hadn't really considered they would be bad but I will have a look this weekend.

Terminal_Boy · 24 Oct 2019 at 09:05

Invertigo said:
From the service history the plugs were changed last year before purchase, so I hadn't really considered they would be bad but I will have a look this weekend.

It’s well worth checking as sometimes a tick on the service history doesn’t mean it actually happened.

Also check the air filter is clean and seated correctly. Same goes for all the air intake ducting - check for splits in the hoses and that all the clamps are tight.

MatteH Oxford · 24 Oct 2019 at 09:42

Invertigo said:
No codes stored at all, no warning lights etc.

If you have live data available from a scan tool, the first thing I'd do (after checking obvious visual items under the bonnet) is to check the fuel trim to see if the ECU is either adding or subtracting fuel i.e. running rich or lean. That will give you more direction in diagnosis.