You're expecting somewhere from 0psi to 150 (ish) so no use getting a diesel one where you'd want a 0-500psi gauge. 0-200 would be good but you might have to get a 0-300psi one which would be fine. Stupid cheap on ebay I noticed, £7? lol Your plugs are 12mm (or ae they 14mm? ) but they mostly come with adaptors to fit a range of sizes. If you were old school you'd have one with a fits all rubber end to hold against the plug hole, take all the plugs out, spin the engine and test all 4 in a jiffy. To do the test, pull all the plugs to save the battery fighting compression and hold the throttle fully open. Half a dozen ur-ur-ur should get it to max even on a worn one. A good one would get to max in 2 or 3... depending also on how fast you can spin the engine. If you get a low one you can always give it a desperate 10 compression revs to check.
Tappets reset correctly and problem is better, but still there. So, cold compression test results are in @Zed : - Cylinder 1 - 110 Cylinder 2 - 105 Cylinder 3 - 120 Cylinder 4 - 115 They're all around the same figure which is OK (none are stupidly low). However, when taking plug 4 out, the centre of the plug cap stayed on the plug so looks like it's time for replacement (probably hasn't helped my problem).
While all of the figures are OK, there is more than 10PSI difference between them, so things aren't perfect. But disintegrating ignition leads can cause misfires.. I was using the same leads for years, and on my No2 lead I started noticing that I could get slight shocks off the lead touching it just behind the plug insulator, not on the other leads, and there was a slight occasional shudder when idling.
So the problem is still there - when the engine is warm from being driven and under very light throttle (at around 45mph in top), it will misfire/backfire occasionally (not every 4th stroke which makes it difficult). I'll need to get Mrs M driving so I can lie on the R&R bed looking into the engine bay to see if I can identify it further. What's been done so far? Petronix Flamethrower swapped for 123 Ignition. Timing set for 7.5degress (both with and without the vacuum connected). I checked the tappets and they were out on #3 cylinder so I adjusted them (I'll check them again this week to see if anything has changed in the 20 miles I've done since then). When checking compression, one of the plug leads fell apart so all four leads and coil lead have been swapped out for new. Swapped the coil for a new one to rule out a coil problem (have put the old one back on as it didn't make any difference and keep the new one for spare). The carbs have had new spindle bushes and needles fitted. No air leaks around the carbs as a generous spray of carb cleaner around any areas where there could be an air leak didn't change the running of the engine (before the spindle bushes were changed, the engine 'stumbled' when I sprayed carb cleaner on the spindles). Carbs have been balanced. Plugs have been cleaned and checked for gap before putting back in again. I take it for a test drive after every check/change to make see if the problem is still there. What to look at next? This is where I need help guys. The next logical step is heads off to inspect etc. Or is it the next logical step?
New plugs were put in when I serviced it in Jan/Feb. Didn't make any difference but good suggestion. #3 was tight (no gap).
I don't know what a 123 does but have you got a timing light and have you checked what max advance is with the vacuum line plugged. On a stock distributor if I start at 7.5 degrees static, I get about 30 degrees at about 2000 rpm. I think with a light you'd also be able to see the blips as it misfires.
The 123 Ignition is an advanced electronic distributor (linky) and timing is set at 7.5 BTDC with a light. The problem I have, is that I cannot reproduce the problem when stationary - which makes it really (really) difficult to pin it down.
7.5deg BTDC is just to get the engine started, then adjust to 30deg at maximum advance. But the timing being a bit out isn't the problem. You seem to have checked just about everything and I have no answer - but I'd still try a new set of plugs. Just some random thoughts: Are you using the rotor arm and cap that came with the 123? Which curve are you using, or is it a programmable 123? Is the engine 1700, or did someone tell you it is? Are there any part numbers on the heads (under the rocker covers)? It's curious that #3 has fairly good compression but that was the one with a tight tappet. The other cylinder compressions are okay but on the low side suggesting it's a tired engine. Type 4 cams wear and I wonder if the valve lift is less than it should be – if you have a dial indicator it's easy to measure. What is the fuel additive supposed to do? I'd stop using it anyway. Does the misfire occur with a near empty tank or regardless of how much fuel there is? Have you checked the carb float chambers for water?
It could be worth taking the jets out of the carburettors one at a time and reading the numbers on the jets, checking that all idle jets are the same, main jets are the same, air corrector jets are the same in each carburettor.. then if the numbers are the same, you might have to be comparing pairs of identical functionality jets in case somebody reamed out one or the other.. On mine a subtle stumble at light throttle turned out to be a drip of fuel from the carburettor as the needle valve gave up.. It was prevented from filling up the engine by a cutoff solenoid, but one time I stopped before it warmed up , and it was gently stumbling.. then it flooded leaving me at the roadside for 40 mins until the petrol boiled off.
Thanks for the suggestions - answers in order you asked For a 123 Ignition distributor, you don't need to set it to 30deg at maximum advance - the electronics handle that for you. (just re-read the manual, will double check the timing again later). The 123 Ignition is new with the rota arm and cap that came with it. Using the standard curve on the 123 Ignition - but the problem was there before I installed the new distributor It's got a 1700 fan cover, an 1800 block, and 2000 on the V5 - so anyone's guess as to what the exact size is. I know it's a type 4 though Will have to check the part numbers on the heads next time I'm under the van Don't have a dial indicator...but I know what they look like Will redo the compression tests again later in the week (giving it half a dozen nur-nur-nur's) per cylinder to make sure I did them correctly. I'm 99% certain I did them right first time, but it's easy to repeat. I've used the fuel additive since I got the van on the recommendation of Mike @ Way Out Westie to help minimise the effects of E10 on the fuel lines, carbs etc. I've done 3000 miles+ in it when using that, so it's not a recent change. It can happen regardless of how much fuel is in it.
The carbs have recently been stripped, cleaned and viton needles fitted along with new spindle bushes and floats. One thing I haven't checked is that the fuel regulator is delivering enough PSI on the fuel.
I understand that a dry test result and then a wet test (a bit of oil in each, quick turn over to spread and then test as dry) will tests for leaks and show up if the results differ...the others on here will be able to suggest if this is not the case.
No, the 123 switch is clever but it isn't that clever, it simply adds advance to the 7.5deg depending on the curve you select. But I think you can say the problem isn't the distributor or the timing. '72 and '73 model year might have had a 1700, '74 and '75 1800, '76 on would have been 2.0l. The v5 and 6 rib box suggests your bus had a 2.0l but as the engine has been replaced it could be anything from 1700 to 2.6l or more. The head part number would be a clue. But zeds 2.4l has 1700 heads and my 2.3l has 1800. Compression test with all plugs out, a fully charged battery and the throttle wide open. Crank until the pressure stops increasing. Did the problem start after the carbs were rebuilt?
Problem started December time. Drive the van regularly and had done nothing to it for a few months before it started.
If it wasn't, it would show itself when the engine was demanding the most fuel for a prolonged period - up a long motorway hill with your foot on the floor.
