MG ZT 1.8T Harsh Sudden Hesitation Followed by Harsh Jerking When Heavy Accelerating
 

Hi all!

nice to see so many likeminded people with great taste in cars! im pretty new to forums to i apologise in advance if i do anything wrong


so, to the issue!

i have an MG ZT 1.8T 53 Plate, the previous engine had no compression cylinder 3 so i decided to get a new engine.

i checked all the engine, no marks or scores in the bores, pistons looked pretty new, i had the head pressure tested and skimmed - all came back ok. did a headgasket, cambelt and water pump, new inlet exhaust and cam cover gaskets, plugs, air filter oil and oil filter. i checked the turbo - all ok, and replaced the oil return gasket.

it has since run a little rough when cold, but idles great when warm.

if you harsh accelerate it gets to roughly 3-4k and there is a harsh hesitation that throws you forward in your seat, the only way i can explain it is harsh hesitation / jerking

this only happens when harsh accelerating, if you slowly accelerate the car will run fine and boost like a goodun.

if you really push it to make the harsh hesitation/jerking happen it brings up the EML which are these codes:

P0445 - Control Purge Valve Short Circuit To Battery/Ground
P0444 - Control Purge Valve Open Circuit
P0234 Refer To OEM Repair Information For Code Description
P1300 Misfire
P0170 Fuel System Adaption Out Of Range
P0300 Random Cylinder Misfire

if you drive it normally after the EML comes on, the EML goes out and the fault doesn't return until you turn the car off and on again

if there is any more information you guys want i am happy to give it!

sorry if i have missed anything!

On a 1.8T throwing 0300 code i would first replace the ignitions coils and leads - i have had similar symptoms some years ago and that resolved the issue.

Would not penny pinch on new coils get good quality/OEM ones.:shrug:

I have no experience of the 1.8s but I would say the issue is fuel or ignition.

good luck

macafee2

(this only happens when harsh accelerating, if you slowly accelerate the car will run fine and boost like a goodun)

I know you checked your turbo but possibly you could have turbo over boost, among your issues which will cause the engine to hesitate and miss fire before continuing (it cuts the ECU) . check your turbo control hoses for any splits or loose fittings , From experience pipes can be pushed too far into the elbows blocking flow. I take it you checked the waste gate for operation as the have been known to seize . Yorkshire GOK gave a valid suggestion , Also check your plug gaps

thanks for the advice!

i still have the coils from the other engine - i kept a few bits in case i needed them - so i will try this tonight and report back

Thanks for the advice!

i've just done both A/C rad and coolant rad and did find the turbo intake pipe wasnt tight, so i've done it up and the problem still persists but is alot less harsh

i have to do the intercooler when it arrives, so i will double check the turbo pipes and see if anything is ceased or loose. i still have the old turbo so i will make sure its in good condition and worst case will replace the turbo

once the intercooler comes I'll report back!

Do make sure the vacuum hoses to the turbo solenoid are on the correct ports.

Ignition leads are known to break down (ie fall apart) where they connect to the plug and also the carbon ribbon in the leads break, causing the spark to have to jump the gaps as it were. This is worse under load. The cost of a set of leads is minimal and the results can transform the running and fuel economy. If you do change the leads and plugs, make sure that you vacuum out any debris around the plug base before removing them (or risk the stuff going into the cylinder!). I used a 25mm plastic tube taped onto my normal vacuum hose, over the plug. A fair bit of broken plug cap could be seen in my vac's container at the end of the job!;)
Ignition components.

hello all!

so i've changed over the coil packs and leads and the rough running got worse, with a definite misfire. so that is progress!

im thinking of changing out the ones i have for new ones as per your advice. where would i go about getting OEM quality parts?

many thanks!

Jamie

Here ya go:

https://rimmerbros.com/ItemList--Rov...Coils--m-22325