Got a misfire on my 89' SWB Auto on Cylinder 5. that is doing my nut in!!...I've read all the misfire threads and can't get any further...so i'm after pointers before i swap a known Good PTU -

 

FYI...I've cleaned "ALL" connectors as a first port of call and then tried again, same problem.

 

Swapped the Coil pack for a good one (no.4), but the only thing i didn't do like a fool in a rush in the rain the other night was pull the plug or swap for a known good one.

 

I get the following readings on Cylinder 5's coil pack connector;

 

Middle Pin = 14.22v

RH Pin = 0.4mv to earth (2.5v to battery negative) - ?? (see below)

LH Pin = 0.819v

 

Compared these to Cyl 1 & 4;

 

Cylinder 1:

Middle Pin = 14.18v

RH Pin = 3.4mv to earth (5.5v to battery negative) - ?? (above?)

LH Pin = 2.3/2.5V

 

Cylinder 4

Middle Pin = 14.17v

RH Pin = 3.7v to earth

LH Pin = 2.7/2.8V

 

Anyone got any ideas?? I'm thinking PTU or connection to PTU breaking down as this Coil pack wire is actually resting on the plenum and allthough sheided i'm aware of how hot and brittle things can get, but i am getting some voltage and not none...

 

Any further ponters much appreciated

Have you checked the terminals for oxidization on the ptu connectors?

 

While you have your multimeter out, check the ohmage of the coil packs, middle and left pin again, you are looking for 0.7-1.0 ohm, so if the coilpacks are good and within spec you can rule them out.

Also check the ohmage on your injectors, use a large flat screwdriver to lever gently up and careful not to lose the retaining clip, you are looking for 10-14ohms, anything outside this spec it will be over or under fuelling and will also likely to cause a misfire if dead.

 

Next check your maf voltage :

The manual volt test= ~0.8V with ignition on (some people get

0.08V on theTechtom) and ~1.5V at idle. Check for smooth

increase in voltage as revs are increased. A faulty AFM will

often prevent the engine from revving over 2500RPM

 

Also a dead maf will make it run like a pig even if it does rev above 2.5k.

 

If all come back within spec, then check you ptu harness and finally swap ptu.

 

If you can get it on a diagnostic, it will make pinpointing the problem alot easier.

I have cleaned "All Connectors"... and swapped the Coil pack for no.4 which was fine and 5's on 4 is also fine so assume the coil packs are good...I suspect the readings on the coil pack connector for 5 indicate something but not sure what?!!

 

Not measured MAF yet...

 

Have Conzult and have done a drop test but that's about it...No change on 5..

have you checked the injector is firing?

have you checked the injector is firing?

 

Yep. All injectors are clicking away..

Check the injector by ohming it, you need a result of 12-14ohms. Check that plug, if it's old it might be goosed. There is a set of tests you can preform on the ptu for functionality. Once you've done those two cone back and report your findings.

Right guys, Injector Reads 12.7 ohms and Cyl 5 ,2 & 4 Coil packs all reading 1.1ohms then drop to 1.0 (presume this is because they are warm, but all Cylinders other than 5 are running)

 

My original post said misfire, but it is infact not running. Ive had it on Conzult last night and done the drop test before taking it out for a run and then after (when fully up to temp) It seems i might get some firing and this is intermittent as the drop in RPM changes for 5 based on this?

 

Anyone got any further pointers, tests for PTU/CAS or things to try on Conzult?

 

The car has been lying idle for a while (just swapped for a decent battery the other day, and i'm only trying to getting running properly so i can lend it to AnthonyD (I'm at his now!) as he's not only Z'less but Carless as his co. have taken his co. car back while he's convalessing!

 

Any further pointers much appreciated...

Have you pulled the spark plug? What sort of condition is it it?

Pulled the plug and swapped it for another cylinder plug and problem still with . plug looked ok, about to swap PTU

If all electrical tests havent pin pointed the problem, i would look at doing a compression test.

If all electrical tests havent pin pointed the problem, i would look at doing a compression test.

 

I was thinking the very same esp being cyl 5. It's one of the reasons I asked about plug condition, a cyl with low compression will generally burn oil. (Or water obv)

Gents the electricals havent been solved as i have wiered readings on this cylinders coil pack connector as per my original post. Plug was no different to cyl 2 or 4 and was swapped for the one in cylinder 2. I've driven over from mine to Anthony D's (30 miles) so assume i've burned some fuel under compression. If i had compression issues I'd see water out the exhaust. It's teh interpretation of my readings i need in order to pinpoint the fault.

 

Ive just measured again and get 14.1v at centre pin, left pin 1.9mili volts (fixed) 2.0/2.1 on right pin(fixed) when i compared to cylinders 3 and 4 again a moment ago these readings pulse (change) on the left and right pins for cylinders 3 &4...

Basically i'd like to know what the coil pack connectors should read (pulled off) and whether it should be pulsing changing voltages like the other cylinders seem to, and where the voltages for left and right pins, come from? - I'm assuming the CAS and PTU??

 

If the electrics were fine and i had compression issues, then the revs would still change when i pull this coil pack connector.

 

At the moment, when i pull coil pack connector 5 at idle there is no change in engine speed/running. When i rev it there is a noticable cylinder down, keeping the revs up slightly and re-connecting there is a slight change in tone i think...Almost as though reving it provides more voltage..

 

I should have checked the voltages while revving to see what heppens...Will try this maybe tomorrow and see. I'm thinking wiring breakdown or CAS Failure next...

Edited October 24, 201312 yr by TubZ

Plug was lightish brown which was the same as the others. Plug was dry but had been stood 30-40 minutes after a long run.

Gents the electricals havent been solved as i have wiered readings on this cylinders coil pack connector as per my original post. Plug was no different to cyl 2 or 4 and was swapped for the one in cylinder 2. I've driven over from mine to Anthony D's (30 miles) so assume i've burned some fuel under compression. If i had compression issues I'd see water out the exhaust. It's teh interpretation of my readings i need in order to pinpoint the fault.

 

Ive just measured again and get 14.1v at centre pin, left pin 1.9mili volts (fixed) 2.0/2.1 on right pin(fixed) when i compared to cylinders 3 and 4 again a moment ago these readings pulse (change) on the left and right pins for cylinders 3 &4...

 

Never drive a car that's dropped a cylinder if the injector is still firing. Change the oil as soon as you can and hope you haven't glazed the bore.

 

You only get water (as in steam/white smoke) if the head gasket has gone between bore & waterway. I'm assuming the plug doesn't spark when grounded against the plenum?

I didnt say that you have sorted the electrical issues lol , i said if all electrical tests havent pinpointed the problem then do a compression test, obviously you havent finished the electrical side yet, but next step as Noz mentioned, take out the plug at cyl5 connect coilpack and hold the metal body of the plug against the plenum to see if you have spark, if you do then you know its not the coil packs. With balance tube back on obviously :biggrin:

Also use a multimeter to do a continuity test from the ptu plug to coil packs, to eliminate a break in one of the wires.

I solved my cylinder 5 misfire: Although i had cleaned the terminals on the injector and the plug, it didnt run well, so i decided to use a needle file on the terminals of the injector and the plug, squirted to some contact cleaner to clear the debris and it now runs fine with no misfire.

 

So give it another go on the injector cleaning :thumbup1: I had the ohms in spec, i could hear it clicking, but as its on the fuel rail you can sometimes mistake it clicking through the vibration of another along the tube of the fuel rail.

 

The only difference of course is that mine was sill running.