Mystifying "Mis-fire"

[124cso]

I have a F.I. car which has (suddenly) developed a mis in both No.3 & No.4 cylinder.
The car was running fine, then had a lay-up for about 6-8 weeks, then had this severe mis when next started.
The car starts and sounds to run o.k for about 2 or 3 seconds, Then starts to shake and stagger and stalls at anything below about 2000 rpm, at which speed it has an obvious severe mis-fire.
In order to rectify ; I put in new N9YC plugs, had leads checked by auto electrician, tried leads off a 124 Coupe, checked spark from distributor to lead - jumps about 1to 1 & 1/2 inch air gap.
Have run compression tests on cylinders 1,3 & 4 - all similar, so unlikely to be stuck valve/s or burnt head gasket ?
Cranking car over with one plug out at a time, we get fuel fumes out the top of both cylinders so assume injectors working ?

Thought fuel starvation a possablity so replaced filter and had pump checked - o.k. I don't want to pull out injectors if I can help it as so hard to get at & disconnect.
Is it possible dead cylinders sucking enough fuel out of manifold via plennum box to make me think injectors on 3 & 4 working ??
Any ideas or suggestions ?????
I cut the old fuel filter open and it had lots of crap and staining in it but outlet end of element looked clean
I know it is No.3 & No.4 as once running at 2000 rpm, we can unplug those leads with no effect !

[rlux4]

It does sound like those injectors aren't doing thier job. Try a stethoscope on the body of the injectors and see if you hear them clicking. If they're not clicking check the two grounds on the intake plenum. These two grounds are for the injectors with 1&2, 3&4 linked there. If they're clicking, it sounds like they need to be cleaned.
Ron

[narfire]

The injectors LOOK like they are a pain to get at but actually are not really that bad. The leads come off realativly easy as well.
#1&2 I use a bent tip needle nose and 3&4 same or very carefull a large screwdriver from above and an easy twist to loosen and then the rest by hand.
The injectors are held in by a small plate that kinda pushes the large rubber seal into the intake manifold,these are delt with by a 10mm nut. Again first two are easy and the #3&4 by using an extension on your 1/4 drive.
A couple of more things if you do have to take these out, Members have mentioned to me when I had issues, that the inner "O" ring could be pooched(this can let outside air in causing not running right)I believe you can check this by carefully spraying a somewhat volitile liquid around the injectors while car is running(it was suggested carb cleaner) the cylinder will pick this up if there is a leak with the seal. The injector hose itself can break down over time and if you are pulling and manipulating the injectors, they can crack. Bad news if you put them back in when they have fuel at around 35+ psi behind them.(starter is right below) The fuel rail is not difficult as well,you'll see what has to be done there if you want to change out the injector hoses.
As a little safety tip,I did this once wearing my wedding band,and some how came in contact with the starter hot wire and a ground. Big sparks and a 1-2 deg burn around the finger blister ect.
I hope you have an easy problem, sounds like something with the injectors, but try the easy stuff first.. Do you have access to a noids light? I found the 'Geo tracker" fits these injectors.
Good luck, have fun
Chris

[So Cal Mark]

did you perform your compression test with all of the spark plugs removed at the same time? Did anyone mess with the firing order?

[majicwrench]

Injectors would be very low on my list of things that could go wrong. Why would two fail at once?? Big vaccum leak is a guess, but just that. And Mark is right, check the firing order, it is USUALLY something easy and stupid.
A little off topic, I had three cars in the shop this week, all three have had their computers replaced by other shops, guess what, same problems still. One had a broken wire, one had a bad cap, one had an intake leak. Tis (almost) always something easy.
Keith

[pope]

Ron is on to it. Injector 3 and 4 are powered by the same source at the dual relay 88b. Injector 1 and 2 are powered by another source. If your are getting power to the injector connector with a voltage tester with key in and on, then there is a grounding problem.


But, just think of it. A 2-cylinder car would get great gas milage.

[So Cal Mark]

if you're not getting a ground on the injector circuit the noid won't light. The lack of a light doesn't mean you don't have power there

[LE759]

For what it's worth. When you said you checked the leads, are you talking about the leads under the dist. cap? I had the same problem with mine, the car would start right up and then start misfiring. the problem was with one of the leads under the cap grounding out. temporarily taped it up and solved the problem.

[124cso]

Just for information, I have been thru everything else with no change , so bought and installed a set of new injectors off Ebay for $100. Runs sweet as a dream!

[So Cal Mark]

thanks for the update, congrats on getting the car running well again

[rlux4]

Thanks for the update, it helps to hear what worked. One question though, new injectors for $100? Is that apiece, or for each?
Ron

[124cso]

US $100 the set of 4. Could have paid 350 Euros each from Spiderpoint in Germany !

[zachmac]

Just for information, I have been thru everything else with no change , so bought and installed a set of new injectors off Ebay for $100. Runs sweet as a dream!

Good news, congrats. BTW, to reiterate an earlier post, if you don't know the last time it was done pull your injectors and have a reputable shop clean them and check spray patterns. Dirty injectors cause all kinds of problems and stuck open one (like I had) will make you run rich and waste gas. There are usually local shops that can do this properly or there are several places you can send them to to have this done, usually for about $25 per injector. That includes all new external seals and pintels if needed.

Most likely a set off eBay for $100 is a cleaned and refurbished (versus new) set which is fine.

[124cso]

When asked, seller assured me they were NOS, not refurbed. Probably just looked at right time to get a buy-now bargain ?
Made up for the weeks of grief trying to sort it out.

Interestingly, local Bosch service/agent had quoted me "about $75" to put their test gear on the car to (try and) find the fault. This is after I hired a trailer to tow the car in on!

[baltobernie]

You injector guys need to get a set of "known good" ones that you can loan each other for troubleshooting. Can't cost much to mail them around.