Low RPM Miss

[dodgybrumby]

Hello.
We'll my newly acquired '90 Brumby has some issues that I would like your assistance in fixing (hence user name!). I'll do threads as I go, to separate the issues.

First things First. She is a bog stock standard '90 Agquip Brumby (any diff between ag and non ag?). The old girl runs perfect (as much as an old car can!) but 15-20min into driving she will develop a low RPM & low throttle miss.

Now, google has revealed that the fuel line is prone to becoming blocked pre pump. I haven't checked it, but it doesn't sound like the problem.Why?

1.While engine is coughing and surging in the lower RPM with light throttle (ie puling away from lights) if I put the foot down the engine will pull cleanly and without hesitation!

2. If it was a blocked fuel line, it would normally restrict fuel flow. Causing a lean or fuel starvation moment. I would assume that this would happen when there is a max load situation. ie going up a hill. But this only happens under light load/RPM situations. Strange

3. It seems as the engine reaches normal operating temp it is more likely to occur. If it's running fine, but the engine is near normal temp, and I stop for a short time (fuel stop) it will almost always start missing. Almost like heat is causing something to happen. I was thinking maybe coil getting heat soak?

4. The problem comes and goes. It is always fine when starting the engine cold. Then will start missing 15min or so into the trip. Then after some time it will stop, then return again later. Bloody annoying!

I don't want to start replacing things trying to fix it, so if you have a suggestion please tell.

Thanks

[Alex]

do a general sservice.

most common thing that will cause this issue are the leads. They get old and cracked.

first thing id check are the plugs, then the leads, and then the coil. Your dizzy might be on its way also. A new dizzy cap is another thing you should do.

all of this is relatively cheap, and should be replaced anyway

also replace your fuel filter. Pretty common to get clogged at that age. Im doubtful the fuel lines will get clogged. Never really heard of it before.

other than that, its a great car and the old ea81 is a bulletproof motor. Have fun

cheers

alex

[dodgybrumby]

Thanks Alex. Yeah that's the way I was heading (ignition fault of some sort.)

But all looks good. The Rotor cap is a bit rough, but shouldn't cause a intermittent fault.
Fuel filters are new. Another one I found while googling, was faulty (cutting out) fuel pump. That, to me at least doesn't sound like it though. Especially since when I put the foot down, mid cough, she revs clean.

Ok. Just been out to look at the old girl and got some photo's below. All looks fairly normal right? Well the end of the air inlet is swan off (+10hp there!) and a couple of vacuum hoses not connected and are blocked off.

In the photo that shows inside the filter housing, the thing that's on the far left is not connected. Is this important? It appears the carby has been off at some fairly recent stage.

Bugger me I hope it's not carby, I hate working on those things. Give me Diesel and Hydraulics anyday.

[steptoe]

it could just be a niggly little pollution hose on or near, to or from the carby. Light cruise throttle sounds like the EGR function time. Maybe see if it is getting its vacuum supply. Try what I have done T in a new vac line to incabin to a spare EGR valve to feel when it works little finger poked inside it. See if that is when your problem is, or try block off EGR on manifold totally, likely to be all carboned up in 21 years. You just bought it ? A good bit of advice is go buy and fit a full tune up. Dizzy cap, rotor leads plugs air oil and fuel filters there is two on a brumby. Subaru sell an intake cleaner in a pressure can for about $17 . It is , or half is sprayed into an intake manifold hose to let it expand and clean internally on a hot engine, run and see all the crap blow out the tail pipe. Comp test and tappet clearances a good check too - being a Diesel dude you'll appreciate that

[dodgybrumby]

I wonder if it could be the vacume advance on the Dizzy?
When I push the plunger in and block the vac line, the plunger will come out.
Anyone know if you can get these on there own?

[dodgybrumby]

Well the miss is gone!
I had a poke around in the bay for some time and pulled vac hoses off and on, generally just had a play, and it's stopped!! So would assume that there was a vacume leak of some sort causing the problem.

However I did notice that there is a small idler pully on the front of the engine that has, recently it would appear, had a v-belt running on it. The bracket up near the alternator has some marks that would indicate that perhaps a A/C compressor once lived there!
There are no remains of the A/C to be seen in the engine bay, or on the dash. Is there a way to confirm weather or not it had it? Like a component that gets changed or modified to suit A/C?
Might need a new thread for this! It's getting hot and I'm not going to enjoy summer in this!

[steptoe]

engine may well have had AC but not in your Brumby. Most had an in dash AC switch in the central panel

[kj0]

I had a similar issue with my Gazelle. however it was due to an injector missing a o-ring. Don't know where it went but Air was getting into the pistons along with fuel and this was with no throttle at all. If I rev'd the engine as soon as I started her up, it would die. So at lights i would have to slow up in neutral being ready to pull on the handbrake in just enough time to not do anything but halt and hold the car. sit at the lights in neutral whilst putting in a little throttle, then I would have to be quick enough to hill start on a flat surface before it died.


Sorry doesn't quite help, but maybe the cause is along those lines somewhere of extra Air getting in.