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View Full Version : s40 t-4 hesitating top end of rev range


phelpsy-t4
Thursday 15th July 2010, 12:25
my s40 t-4 revs normally up to about 4000rpm then hesitates slightly, almost feels like it misses. iv got brand new sparks fitted so not them. any ideas guys please let me know. cheers
t5_monkey
Thursday 15th July 2010, 13:59
whats your intake temps like?... get it on a dyno with an AFR plot - that should flag up any fuelling issues.
gmotS40T4
Thursday 15th July 2010, 14:13
Beginning of the end for a coil pack? or possibly a dirty MAF?
LiamT4
Thursday 15th July 2010, 16:23
Beginning of the end for a coil pack? or possibly a dirty MAF?

What he said, or maybe a faulty lambda sensor, but that should also bring up the engine emissions light. Has it been happening for long? Do you use normal petrol (not v-power or similar)? Sorry for the questions, but there are quite a few things that could also be the problem.
gmain1967
Thursday 15th July 2010, 21:45
Beginning of the end for a coil pack? or possibly a dirty MAF?

I'd go with above and one other possibility. Check that the HT leads are all fully pushed home on the plug end. If they are not, it may run OK at lower rpm but at higher rpm and current, will lose spark.

Additionally, clean MAF (with contact cleaner), and the electrical plug for the MAF itself.
JUDGENINJA
Thursday 15th July 2010, 22:19
I had the same problem a few months ago. Do the servicing thing

Replace both coil packs, leads and plugs...

I tried to fault find by buying one and it didn't work...
phelpsy-t4
Friday 16th July 2010, 12:28
CHEERS guys..il be all over it this weekend and il let you know how it goes. the 290bhp baby will be fit and healthy soon :-)
The-Les
Sunday 25th July 2010, 09:40
I've got the same problem btween 3500 and 4000rpm. done all the above except for the lambada sensor. does antone know if a 1998 t4 have two sensors or one? I'm thinking of making a custom exhast when I replace it.
LiamT4
Sunday 25th July 2010, 22:58
I've got the same problem btween 3500 and 4000rpm. done all the above except for the lambada sensor. does antone know if a 1998 t4 have two sensors or one? I'm thinking of making a custom exhast when I replace it.

A t4 has 2 lambda's. If there is a lambda problem that is effecting the performance than it will be the 1st lambda (before the cat), as the 2nd lambda just measures the gases to see whether the cat is working. Its the 1st which is the important 1 as it helps adjust the fuel mixture etc.