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88 Turbo ( carby's) no power over 3000 revs - Induction/Turbo/Chargecooler/Manifold/Exhaust - The Lotus Forums Jump to content
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stevem

88 Turbo ( carby's) no power over 3000 revs

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Hi guys

We went on our Sydney day out on Sunday, my Esprit ran very well for the first 200 miles and then suddenly developed a problem ( whilst DanR was driving it ! ) Before the problem occurred, the car was pulling very well, turbo boost OK but a slight smell of fuel when pulling up hills - this might be a clue.

Suddenly and whilst running, setting off from traffic lights on the way home the car wouldn't get over 3000 revs and had no power. Turbo boost is coming on over 2500 revs, but popping can be heard from the air intake and the car won't pull at all. On the flat using gears I can get up some speed, but as soon as a hill comes along, nothing.

When the engine had cooled down after a cup of coffee and a think at Dan's place, the car ran OK again until normal operating tempearture was reached, and then no power. Good news is that I got home OK, slowly but safely.

At first I thought it may be a vacuum advance problem, I have replaced all the vac hoses, but no change. It still runs OK cold, but not when warmed up. I'm now thinking fuel problem, but why would that be related to heat - fuel cavitating / vaporising in a duff pump maybe ?

There's no cat fitted, fuel tanks 3/4 full, good spark, turbo boost pressure, carby's, not fuel injected - has to be fuel related. Any ideas ? I'll se if i can pick up a pressure gauge tomorrow to test the fuel pump / regulator.

Part 2 detective.gif a few hours later

I have done some basic fuel checks. I disconnected the fuel feed from the regulator inlet, Fuel pump runs and pump lots of fuel very quickly, filled a 5 litre can in no time at all so I would say pump is OK.

Next I looked at the feed from the regulator to the carbs, again lots of fuel pumps through the regulator and the flow varies as I blow/suck gently into the small vac port on the regulator, so I would say that is OK too. So not fuel then.........

Back to the vacuum advance. What if the thermo valve has gone bad and when the engine comes up above 70C the vac from the carbs to the dizzy is cut off. I have now bypassed the green thermo valve and need to take it for a run and see if it's changed anything. Trouble is - just looked at the front drivers side tyre and it's completely flat. that's it for tonight, but any other suggestions welcome.

Cheers.

Part 3......

Spare tyre on, test drive. This time there is no power even with the engine cold which surely is a clue as the green thermal valve is now bypassed, and the carb's are connected directly to the distributor. With the green valve connected normally there is power until the engine heats up.

Edited by stevem

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Inside the unions where the fuel pipes attatch to the carbs there are tiny filters made of a fine gauze.

You need to unbolt the fitting from the carb to see them. Gotta be worth a check..?

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Thanks Simon, I'll check those today. The temperature component in this is baffling me, why does it run OK until warmed up ? The fuel, spark and air intake/turbo are all working OK below normal operating temperature, but when it warms up something changes. It's not a gradual thing either, one second I have power and then it's gone and it seems to happen when the temperature gauge reads around 70C. The only things that could effect that as far as I can see are the brown and green thermo valves and the thermally controlled ignition solenoid in teh engine magaement system. I know that bypassing the green thermo valve makes the car run bad at low tempertures too, so that has to be a big clue. I have studied the attached diagram and can't work out in my mind what effects what. I'll start making some subtle changes to see if anything becomes obvious. Something failed/changed whilst on a run, so maybe a valve went bad or a hose became blocked.

On the carb's there is a black/white hose that goes from corner of Carb2 back to teh dizzy via the green thermo valve which effects ignition advance, but what is the black pipe that goes into both carbs from the brown thermo valve, via the crank case one-way valve ? What effect does that have on the system ?

post-5938-127413347323.jpg

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"The temperature component in this is baffling me, why does it run OK until warmed up"

The less fuel volume the easier it will vaporise, so if it's restricted (blocked fuel filter) or less than efficient pump the less temperature you need to vaporise the fuel.

Could be, :thumbsup:

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That makes sense, but the fuel pump is running OK and delivering lots of fuel, though I only tested flow not pressure. Could it be that the fuel pump impellor 'stalls' when under pressure but runs ok when the outflow is unrestricted ? I'll try and find a pressure gauge to check it's pressure. I can get a pump for about $200, but it's an expensive purchase if it doesn't fix the problem.

The other option is that maybe the temperature thing is fooling me ? What if it's just that the car has been stopped for a while, and it runs ok for a few minutes after starting before going bad - time factor related. Fuel pressure drops off for example.

I'm going to check over all the ignition connections and change the spark plugs tonight, because I can't think of anything else to check right now.

Because the car runs OK for a short while ( or when cool ) the basics are all there, fuel, spark, air. The turbo is working and the gauge shows boost, so no blockage there. There's no cat, so it's not blocked, the oil is nice and clean ( changed it a few weeks ago ) no sign of mayonaise so not a head gasket problem.

i've given up on the engine management side of things, replaced many of the vac hoses, tested vac, plenum pressure, etc and all is OK. Maybe the Distributor has a problem and the advance isn't working properly. ( but then it wouldn't have power when starting from cold ). Bugger.

When it starts playing up, the turbo starts spooling and boost pressure rises, but then the air intake goes from a nice 'whoosh' to a popping/choking sound. I have to change gear at around 2800 revs, but very little power.

Sparky - fancy a trip to Oz ?ice.gif

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Looking at the diagram, when cold the green valve looks like it diverts vacuum to provide a throttle jack and alter the advance to promote rapid engine warm up. If it's not switching ports when warm then it would carrying on affecting the spark advance. Have you tried bypassing the valve by connecting port D to port 2 when warm to simulate the changeover?

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Not sure if this is relevant but I had same issue last week see other post on Turbo issue below this one.

My car was running fine then lost all power suddenly above 3000 revs. It would not go above 90-100mph in either 3rd, 4th or 5th gears and struggled to maintain 60mph up a slight hill.

Switch her off let her cool down and all was well. she'd boost pull al the way through to increased redline 7800 and no problems until she'd warmed up again. Then same problem nothing over 3000rpm and rough running.

Turned out my Wastgate was seizing open when the Turbo had warmed up. Cars running as good as ever now its been freed up.

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Steve, take the car out, get it hot do what you normally do when it loses power, but as you do it pull the choke out and report back. Might give us some clues.

Roger

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Hi Roger, pulling out the choke made it splutter more and it stalled. I also checked all the ignition connections and even replaced the spark plugs but there's no difference.

sailorbob, I tried that but no change. I bypassed the green valve altogether too. In fact I did the same with the brown one, and also tried connecting vac directly to the dizzy advance but nothing changed.

On my last test drive the car didn't have enough power to go up my driveway, and I had to tow it back up. It felt like a hill start in 5th gear, ending up in a stall whilst slipping the clutch. ( i was in first ! ) Even after leaving the car an hour to cool down, it had no power so it's worse now than it was before.

I'm all out of ideas. I think the turbo wastegate is OK, I have boost pressure, in fact when the boost starts it's almost like it's blowing out the fire ! Is it possible that a bad fuel pump can deliver a high fuel flow, but not have enough pressure ? It's an inline pump, not in the tank, and I wondered if a generic Walbro pump ( 220l/h) might be OK, available on ebay for $100 and states Ok for turbo cars upto 500bhp, or does it have to be a special 'lotus' item. I have read 3 other threads about similar problems being cured by a new pump so might get one anyway.

What ever it is, it happened in just a few seconds whilst out on a long drive, one minute all was well, the next power was lost.

Edited by stevem

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Some progress today. I borrowed a fuel pump pressure gauge and hoses from a local mechanic ( he was strangely very helpful ) and found that the fuel pump will push 20psi before starting to stall. On the carby side of the regulator, at idle the fuel pressure is 3psi and rises as boost pressure is applied to the boost tube. With 10psi of boost pressure ( from a small compressor ) the fuel pressure is just under 15 psi, which is just about within design spec of boost pressure + 4psi.. So the problem is not fuel pump related.

thumbsup.gifanimier.gifcheers.gifbounce.gif

it's FIXED !!

Ok, Once I found the problem it took 10 seconds to fix it, and it cost me nothing. Guess anyone ?

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I know the answer and if Steve is offering a prize, I'm open to bribery. evil.gif

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OK thrill seekers......secret.gif

The problem was that the four banjo fittings on top of the carbs that attach the balance pipes had vibrated loose. The carbs were rebuilt about 4000 miles ago just before I purchased the car, and they must never have been tightened up enough when put back together.

The 200 mile drive on the old Sydney back-roads must have jiggled them loose. That would explain the smell of petrol under load going up hills too, which I could smell a couple of hours before the car lost power.

All good in the end, most of the vac pipes are replaced with new ones now, and I learned a bit along the way about the engine management system and ignition.

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That's good Steve, I'm glad I didn't break it. :D

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