Loss of power on V8

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Lotty

New Member
Posts
8
Hello everyone,
We are momentarily in Maroc and have been expereincing blowback problems since we left the UK which seem inpossible to understand!!Here is the full storie with all the details which hopefully bring possible solutions!

The car in question is an old militaryvehicle, from 1986, sold in 2003 to normal citizens. The car is a twin carb v8 3.5 litres. We are not sure wheter engine is pre 1986 or after, as it is a changeover year. It mihght not even be the orgiginal engine as there is a plague saying it was a 2.5 turbo diesel, but this could just been added after.

It has a new waterpump, and the last two parts of the exhaust are new, the coil is new, the distributor seems to be new also.

Two days before leaving the UK we had these two parts of the exhaust changed and used the parts of before the changeover in 1986 as was the advise of the mechanic. Maybe we should have used the parts for 1986 onwards as it was on our first trip leaving the UK that we started experiencing blowbacks. Does anyone have expereince with the resuls of wrong exhaust parts???

The problem is as folllows: there seem to be a small blowout on the exhaust and every so often a blowback (ignition fumes). It feels as if there is a misfiring or lack of fuel, as if someone slammed the brake. The is a sudden loss of power which then just as sudden, after 1-2secs comes back as normal.
Our right carburator (drivers site) damper pops op every couple of hours driving especially when puttin strains on engine such as in hilly areas or high speed motorways. The left damper (passenger side) also comes of every so often but not as much. Our distributor seems new, points are good, wires seem new and have just spaced all wires of away from engine. It is when carb spout pops out and up to the moment of us stopping and putting it back on that car seems to lose power and ability to drive uphill, also affecting excelleration. Machanics checked fuel flow by removing fuelfilter qnd flow was uninterupted. The blowbacks seem to come from where final exhaust section meets the manifold. Of the three bolts connecting these 1 appears loser than the other. A family friend suggested this as the problem yet machanic said a blowout of air is prefereable for engine than leaving hot air in the exhaust. Still we tried tightening it which resulted in the disapaering of the loss of power problem, yet more common blowouts with big bangs. However, not changing anything after the problem came back after a couple of hours. We did fill whole in exhaust but this was blownout soon after (so not such good home repair!!!) and we think this might just be a coincedence.
Problem ccurs mainly on motorway when driving around 65mph, but also around 35 and 15 and at other less specififc intervals.

We seem to have slight ooil leak as we seem to use 1l oil ever 500K. However no visibe leak but droplets have formed on bottom of oil sum. Water also has to be topped very often ( but then we are in Marocco).

The oil in the carbs had evaporated but now been refilled which made no difference (unlike 3rd mechanics assumption). Is it normal for the damper to come off and why is so? We have also just discovered that the two carb spouts are slightly different and have today changed them around to see what happens next.

We have absolutely racked our brains, mechanics either dont know or give incorrect solutions and then dont know. please help!!!
Cheers Lotty
 
The oil in the carbs had evaporated but now been refilled which made no difference (unlike 3rd mechanics assumption). Is it normal for the damper to come off and why is so? We have also just discovered that the two carb spouts are slightly different and have today changed them around to see what happens next.

We have absolutely racked our brains, mechanics either dont know or give incorrect solutions and then dont know. please help!!!
Cheers Lotty

Hi there

My guess is that unburnt fuel is entering the exhaust and igniting through the air leak. The badly fitting exhaust has shown up a fuelling/ignition fault which.

Firstly, which carbs do you have? SU's or Strombergs? If its Strombergs I would bet money that it's your carb diaphragms that are perished. This would cause erratic fuelling - and lean fuelling when accelerating causing a loss of power - and the lean fuel mixture is then igniting in the exhaust. The blowback could be popping the carb dashpots up. Are the threads on the dashpot damper threads damaged too? Topping up the oil will not help because the oil will get sucked into the inlet tract very quickly.

Another possible contributory fault may be the ignition timing. What distributor do you have also? Is it an electronic one or is it a sliding points version? Worn or the wrong points can also cause similar sounding backfires into the exhaust manifold. I would check the points operation, dwell, and have a very through check for a vacuum leak around the inlet manifold. Check all the hoses, pinch them and listen for air hissing and erratic idle.

Don't treat the symptoms - look for an underlying fault.:) Best of luck.
 
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