Poor running K Jet

[Joe of Loath]

Hey all

On my way back from a week away and my 740 (KJet B230E engine) is running really rough. Idle is lumpy, and revving it from idle it sounds like it's running on three cylinders and shakes around on its mounts until it gets to 2000rpm, and if I let off before it gets there it backfires. It also feels like it's lugging when I pull away, despite being in 1st gear at 2000rpm or so. Once I get to around 3000rpm it drives fine but is still down on power and I can smell unburned fuel in the exhaust.

Anything I can check on the road (I have all my tools) or should I just try drive it home? I'm thinking the issue is ignition but have no idea what brought it on.

Thanks!

[Clan]

Originally Posted by Joe of Loath

Hey all

On my way back from a week away and my 740 (KJet B230E engine) is running really rough. Idle is lumpy, and revving it from idle it sounds like it's running on three cylinders and shakes around on its mounts until it gets to 2000rpm, and if I let off before it gets there it backfires. It also feels like it's lugging when I pull away, despite being in 1st gear at 2000rpm or so. Once I get to around 3000rpm it drives fine but is still down on power and I can smell unburned fuel in the exhaust.

Anything I can check on the road (I have all my tools) or should I just try drive it home? I'm thinking the issue is ignition but have no idea what brought it on.

Thanks!

first thoughts are an air leak into the induction system , you could take a look inside the distributor cap too . This is a very reliable fuel and ignition system , never gave trouble in it's day and should not today ..

the injector holders are prone to leaking air when neglected , try pouring some water over the injectors when idling , if you get a change of running an air leak there for sure .

[Joe of Loath]

Cheers, distributor looked brand new when I checked it a month or two ago and I've done maybe 1500 miles since then (timing might be off but nothing changed between driving to Cornwall and then driving back...). I checked the plugs and they looked fine (gapped perfectly) other than some white oil residue (I had an issue with the PCV which caused it to burn oil - all fixed ish).

After driving it home, I'm wondering if it might be fuel related after all. I'm going to try your suggestion with the injector seals, and also swap in another fuel pump and fuel pump relay. It was surging for a second or two at a time then slowing down to how it was before (chugging along), when surging it felt and sounded more normal.

Thanks!

[aardvarkash10]

backfires and rough idle/low end and unburnt fuel are all classic cam timing indicators.

Reluctant as I am usually to point before using gauges, I'd check the cam belt...

[Joe of Loath]

This from the FAQ describes the issue perfectly:

Poor Power; Poor Engine Response. [Symptoms] Symptoms: no power under 3K RPM; poor power after 3K RPM; no engine response, very slow response; will not brake-boost past 2 psi; idle fluctuation between 750-1200RPM; rough idle; engine makes loud bog noise from intake when throttle is opened and takes several seconds to respond, even in neutral. Does not seem to get terrible gas mileage, but could be better. Does not smoke white, blue or black. Spark plugs are white on the electrode and have black carbon around the face.

[Duane Hoberg] Based upon an age-old experiences, it appears that your ignition timing is off (late)and is not responding properly contrary to what the base timing light indicates. The plugs with white center indicate a lean fire condition, the black ring indicates a rich, incomplete burn cycle. ie, fuel being burned late in the power stroke or after the exhaust valve is open. Late ignition timing. The ECU via the O2 sensors is leaning the mixture out after they enter the cycle because of the excess oxygen from the interupted incomplete burn after the exhaust valve opens. Causes: Ignition wires not in the proper sequence. Certain engines will run but with little power if two ignition wires are swapped. Has the flywheel been removed and replaced lately? Flywheel off by one bolt or backwards would cause a lot of problems. If the flywheel and everything else is on the money, the ignition portion of the ECU is at fault. Verification via diagnoses step by step with a Volvo Service Manual would be well worth the 20 or so dollars for the manual.

Symptom: Engine with flywheel rpm sensor (LH2.4 or Rex/Regina) will not rev above a certain rpm. Solution: while changing the timing belt, the owner used a screwdriver to secure the flywheel, inadvertently bending the rpm sensor plate. Once that was repaired, the symptom disappeared.

However, Kjet uses a distributor rather than ECU ignition timing, so it's set mechanically, and the only work I did under the bonnet between it working and not working was tweak the throttle linkage and tighten the accessory belts.

[Laird Scooby]

When you were doing the belts and throttle linkage, you didn't knock a vacuum hose off somewhere or accidentally poke a hole in the rubber sock between the fuel distributor and inlet manifold?

Clans idea about the fuel injector seals could be it as well, mine were pretty shot on my last 740 and caused a minor version of what you've got.

However a closer comparison is what Ash has suggested. My cam belt was horrendously loose causing the cam (and therefore ignition) timing to wander about. I did have a video but have lost it (Thanks Photobuck'ay ) showing how much slack was on the belt.

This was a gradual onset thing though, not sudden as your problem seems to be.
I'd check all the vacuum/air/fuel hoses to make sure there aren't any leaks, perished or broken pipes.

If it gets too bad to drive, do you have breakdown cover?

[Joe of Loath]

I didn't knock anything as far as I know, but obviously if I thought I had I would have checked... I found a loose hose on the auxiliary air valve feed which I tightened, but that didn't make a difference.

It was a gradual thing, it started missing and surging while driving around Cornwall but seemed to clear up after a little while, although I thought it felt a little down on power. The first 1/3 of my journey was fine, but things started going wrong on the A30 past Bodmin. By Swindon I'd lost so much power I was in 4th up the very small hill leading up to J16 on the M4. I've not replaced the cam belt since I got it, but planned to at some point. I didn't think I needed to rush into it as the rest of the car seemed to have been taken care of fairly recently (new plugs, distributor, starter motor etc).

Yes, I have breakdown cover but no homestart (as I have two cars and can just drive the other and fix the broken one another day).

I start a new job tomorrow so finding the time, motivation and money required to fix it might take a little while. In the mean time I'm off hunting for leaks...

[Laird Scooby]

Ah-ha! New information! Sounds more like plugs breaking down with those extra symptoms. Worth checking everything really, just to be sure!

What make of plugs are in it now?

[aardvarkash10]

crap blocking or restricting the movement and/or the metering valve of the metering unit is another possibility consistent with the symptoms.

This would give a lean condition until enough airflow lifts the metering plate sufficiently.

K Jet metering units run particularly close tolerances and it only needs a minute piece of rubbish to cause real problems. Not assisted by the fact that not many people know how the damn thing works.

Again, an educated guess, and again, a suggestion that diagnostic tooling will make identifying the problem easier.

[Joe of Loath]

Not sure on the plugs, will check tomorrow. They're gapped properly but have white deposits on them.

Crap on the metering plate like say, some oil that leaked into the intake and soaked everything?