linderpat

"Misfire....kill the sonofabitch!"

LT Texan

Ed, you mean Pittsburg, former city of champions?

dogleg

no they (the injectors) were in tight with a good seal. just that they unscrewed out as easy as a spark plug,which is great because i had read on here they often spin in the alloy outer nut and have to be removed with a vicegrips.had the vac system checked by smoke test, fully sealed no leaks.

LT Texan

That's what mine looked like.

If you confirm you are getting spark still need to confirm you are getting fuel. Which you will need to do even with new injectors.

I worry that if spark is okay, you've got a gunked up fuel distributor only flowing fuel to some injectors.

linderpat

Jeesh Dan, don't remind me.



BTW, what was the consensus on the green wire? Was there follow up with that suggestion?

Ducman82

Misfire? Rack, Tap. Bang... that always fixes it for me.....

LT Texan

Sorry, that was mean. What can you expect from a bitter Dallas Cowboy fan?

dr bob

If the car is somewhat new to you and you think you are sorting a misfire, here are some things to think about. First is that most ignition problems get worse as speed and load increase. On the other hand, fuel problems -seem- more noticeable sitting at idle but stil get more severe when under load. Thinking partially-restricted injectors here, apparent misfire would be a lot more pobounced as lost power under load.

After that, pull the plugs for inspection and a new set. While they are out, do a compression check on all cylinders, and write down the results. Compression tests should ideally be done on a warm engine, all plugs out, throttle propped wide open, fuel pump and ingnition fuses removed. Cylinder and valve leakage cause uneven idle, but may smooth out as RPM's (and dynamic cylinder pressures) come up. If the compression test shows low cylinders, a leakdown test may help you isolate the leakage some to valves or pistons.

dogleg

thanks for your advice dr bob what you have stated makes a lot of sense.i have fitted new plugs in the last few weeks,had the compression test in the back of my mind and should have done this at the outset but was kinda hoping this miss was down to basic servicing parts ie fuel filter,air filter,plugs,ht leads or vac/electrical connections i have the injectors stripped out at the moment awaiting the ordered new injectors.i may as well fit these when they arrive and cross everything if unsuccessful the comp test will be next thing i do.

Brett928S2

Hi

I am always amazed by the number of people that think "checking" a dizzy cap or rotor arm is sufficient... it isnt , you CANNOT see any cracks or tracking internally in the plastic...

In any missfire situation, I always advise you CHANGE all ELECTRICAL parts, not check, not look at, not think they are ok...CHANGE FOR NEW....

Because Nitrous NEEDS the best and strongest spark available at all times, I change my dizzy caps and rotor arms EVERY 2 years.

All the best Brett

dogleg

hi brett really fairly sure that my fault is fuel related now because when it does miss or buck a little all i ever have to do is open the throttle a little at any engine or road speed.if i give it 1/4 throttle opening it instantly clears and runs smooth even if rpms at near idle.most change cap and rotor anyway i might as well I've replaced almost ever other service part.thanks for advice will keep the post updated when i solve this fault.

dr bob

Read the thread again from the beginning, and I'm interested in what the machine used to detect a misfire. Common diagnostic 'scopes look at firing voltage on a relative basis to see if and where there are weaknesses in the ignition. Can't really detect a misfire, but you can see some telltales that often point to misfires. Some have a substitute cable between coil and distributor, and sequentially shut down cylinders looking for consistent changes in RPM's as each plug is dropped out.

Assuming that the 'scope showed relatively consistent firing voltages (else you would be changing cap/rotor/wires), the next possible cause is partially obstructed fuel screens in the metering unit. The little metal screens corrode if they are allowed to sit for extended periods without fuel passing through. Problem is exacerbated by ethanol and water in the fuel. There are of course several other possible causes in a CIS system, including weak injector nozzles, sticking pistons and the like. Fuel misfire problems show up as high HC and very low CO values when the exhaust is sniffed forward of any catalytic converters.

dogleg

not sure how it worked but laptop was loaded with information of the 928 model,year,no of cylinders,engine size then electric clip on to coil ht lead and exhaust prob into tail pipe picking up a pulse from exhaust with car running at idle the firing cylinders could be viewed on the screen as it fired lights on cylinder graphic staying green if ok coming up yellow to register a fault.i watched it show up 2 4 5 and 7 which the operator explained were showing a misfire.he seem to think injectors were the most likely cause and recommended i change them next.

jpitman2

FWIW I have had occasional misfires in my 83 CIS a few years ago. I could isolate the cylinder by selective plug shorting. I found that cracking open that injector's fuel line made the misfire go away. My local wrench opined that this indicated debris inside the fuel distributor - once it got onto the outlet for a cylinder, it would be held there by pressure until it was released by dumping the pressure. Only occurred a few times, and has now been absent several years....Have also done a tank, pump and some hose replacements.
jp 83 Euro S AT 53k

dogleg

interesting, still hoping the new injectors will sort this one should know in the next few days as soon as they arrive.