Hi, my 1988 Sierra 2.8 has i think a misfire, it tickovers slightly uneven, and if you raise the revs a little you can hear a misfire.. I did pull the leads which seemed ok so changed,
Coil
Dizzy cap + rotor arm
Plugs
Leads
Reset tappets
Still runs exactly same but when driving you can feel the poor running through the car, if that makes sense. it just doesnt go like it should.
Just not sure what to check next, and it's my daily driver so need it sorting.. any ideas very welcome


Steve

 

You need to try and isolate it to the cylinder(s) that are misfiring, you have covered the ignition side, I would do a compression test next.

Martin

 

Cheers Martin, it did cross my mind to do one, will sort it in next few days...

Bit of an update, went for a good run down A1 yesterday to pick some downpipes up, even after car is hot i get lots of Vapour from exhaust? and no it doesn't use water either? odd!!

 

It could also be fuel related, it's MFI isn't it?

Martin

 

check spray pattern of injectors
you can rig it up so you depress the plate and get fuel[link out relay etc]
be careful of the fuel mist-its very volatile
if one is pencil it wont be right

thats assuming its kjetronic with metering head...
check for air/breather leaks too,and that injector seals are good

after eliminating all the ht/lt issues of course

 

Hi, Thanks for help lads.. I did a compression test today and all 6 cyls are between 130-140psi, well down on std 167-181psi.. Water has now gone down a bit over half inch, but does explain why it produces so much vapour!!
Time to strip heads off i think!!

 

if they are all very even it may not be an issue i wouldnt expect them all to be down tbh

is battery/starter good? did you hold throttle open while you did test?

check with sniffer and/or borescope while pressurising header tank after exhausting all other checks for water leaks...

 

Hi mate,
damn forgot to hold throttle open, been a very long time since i did a comp check.. i'll do it again though. I'l take it to garage so they can do other checks... Thanks mate