No boost / Low boost condition?

[MadMaxx]

Hello

My 88 has developed a slight problem. The other day while driving, the car just felt a bit wrong. Upon inspection, the boost gauge in the cockpit was not moving. It was below the mark where it usually starts (all the way to the left, below the 1st hash mark by about 3mm) so I thought it had either gotten stuck, or I had a vac leak somewhere. Upon the drive home, the gauge just started working again, but boost levels were low... very low. It's barely moving, almost to the 2nd hash mark on the gauge, and power is down a considerable amount. Now, I thought "Ah crap... turbo failure" at first, but there is no sign of it. No massive smoke, no noise, no oil around the tail pipe interior to give the tell-tale sign of a blown set of seals.

Now, I have the lotus shop manual for this car, and will begin troubleshooting it tomorrow morn. But, if you guys had any specific areas to check I'd appreciate the info.

James

[lotusguy]

MadMaxx said:

Hello My 88 has developed a slight problem. The other day while driving, the car just felt a bit wrong. Upon inspection, the boost gauge in the cockpit was not moving. It was below the mark where it usually starts (all the way to the left, below the 1st hash mark by about 3mm) so I thought it had either gotten stuck, or I had a vac leak somewhere. Upon the drive home, the gauge just started working again, but boost levels were low... very low. It's barely moving, almost to the 2nd hash mark on the gauge, and power is down a considerable amount. Now, I thought "Ah crap... turbo failure" at first, but there is no sign of it. No massive smoke, no noise, no oil around the tail pipe interior to give the tell-tale sign of a blown set of seals. Now, I have the lotus shop manual for this car, and will begin troubleshooting it tomorrow morn. But, if you guys had any specific areas to check I'd appreciate the info. James

James,

I suspect that your condition is the result of a clogged turbo exhaust inlet. Your catalytic converter's ceramic matrix has probably broken and some pieces are restricting the exhaust flow to the turbo.

Ask me how I know this...my car is currently suffering from the same thing, except that whatever ceramic pieces which came loose (I could actually hear the cat rattling) have worked their way further downstream or lodged (temporarily I'm sure) somewhere in the cat, so as of this writing, the car operates perfectly.

It's the end of the driving season here, so I won't address the fix until next spring which is to either replace the cat entirely, or to hollow it out using a broomstick or similar tool to break up and remove whatever remaining ceramic matrix is still inside.

To check this, start the car and slowly work through several RPM ranges with the car in neutral, lifting off suddenly once a set RPM has been reached. Eventually, you'll set up a resonant vibration of the loose material in the cat which you'll be able to hear. This will confirm my diagnosis. However, if you don't hear this, it doesn't mean it isn't the cause of your trouble. Pieces of the matrix may have moved and then lodged into place in such a manner that it restricts the exhaust flow and backs up the pressure. Remove the cat and look inside, shake it to see if anything is loose. Try hooking it up to a shop vac and blow through it in the opposite direction than usual, see what these tests tell you about it. Then replace or eliminate the cat altogether depending on your wallet and eco-consience. Happy Motoring!... Jim'85TE

[MadMaxx]

Lets just say that the material in my cat has already been... ummm........ vacated The valve which has the butterfly in the exhaust (something to do with warmups) is still there however.

I'll hook up my gague tonight to see what the actual readings are. Hopefully, it will be something simple to fix (ha!).

James

[MadMaxx]

I don't think the back pressure solinoid is opening the butterfly. It feels very stiff, where it used to feel like it was a smooth transition between open and closed with my hand. I'm going to let the car reach operating temps and see if it's still closed.

The car isn't producing hardly any boost if any now. The audible spool up "shhhhhhhhhhhh" is gone, replaced by just free reving engine sound.

MM

[cnh1990]

If the EBPV is not centered or has tilted it can cause the butterfly to touch the sides of the flange that is on the muffler pipe side of the butterfly. You can also look directly into the cat by taking the EBPV off just loosening the cat pipe from the turbo then the cat can angle down a bit so you can peer inside of the cat with a flash light.

Calvin

[MadMaxx]

The EBPV is fine.

There is only a single hard vac line going from the outlet on the turbo compressor side to the external wastegate, correct? Do I need to detach this line and apply vac to see if holds pressure? or is there a test port on the unit somewhere I can plug into to do the test? I think the problem is in the wastegate, since the turbo looks fine and there is no sign of oil to signify a blown turbo seal.

Thanks!
James

[tony8169]

This is simple your wastegate has seized in a half open possition, causing no build up of boost pressure, (or very little).
Simply unbolt from the wastegate adaptor and have a look. Piece of cake!! 10 minute job.
Let us know how you got on, Tony.

[igreenrover]

Hi again.

I can't look at my car until the weekend (I work 200 miles away from it during the weeks - very sad!)

Do you think that a seizing wastegate could cause an intermittent fault like this?? If so can it be freed off, or will I need to replace something?

Thanks in advance

[cnh1990]

You can use the pump bulb for the seats to test the operation of the wastegate on the hose leading the wastegate capsule.

Calvin

[dictys]

cnh1990 said:

You can use the pump bulb for the seats to test the operation of the wastegate on the hose leading the wastegate capsule. Calvin

Can you desribe the process, thanks.

Rgds
Dictys 89 se

[cnh1990]

take the hose from the wastegate capsule insert a T into this hose. One end of the T will then attach to a pressure gauge and the other to the seat pump.

It has been a while since I have done this and so I must recheck my manual for the correct figures but I think I pumped the pressure to .65 bar and another time .8 bar to compare. I then measured the the movement of the rod coming out of the capsule and rechecked the adjustment nut of this rod. If anyone has a service manual chime in with the correct settings on the pressure gauge and the rod movement. My manual is sitting at home, so I will have to look at it later and give you the numbers.

The rod must not rotate within the capsule of the diaphram or it will tear rendering the capsule worthless. Only the adjustment nut must be allowed rotate.

Calvin

[MadMaxx]

Calvin,

The 88 FI car doesn't have the actuating rod, or atleast that I could see anyway. There is a single hardline (vac) comming the turbo to the wastegate (way down low).

I think it's all controled by pre-set springs from factory, but I have not opened up the wastegate yet.

James

[lotusguy]

MadMaxx said:

Calvin, The 88 FI car doesn't have the actuating rod, or atleast that I could see anyway. There is a single hardline (vac) comming the turbo to the wastegate (way down low). I think it's all controled by pre-set springs from factory, but I have not opened up the wastegate yet. James

James,

You are correct. The pre-SE cars have what's termed an external wastegate (as opposed to integral wastegate).

Lotus used two models (apparently at random)of external wastegates, a fixed threshold and an adjustable threshold model. The adjustable threshold model is distinguished by the presence of a Cap-head screw w/locknut protruding from the bottom of it, and can be adjusted simply by loosening the locknut and turning the cap screw. This either increases or decreases the pressure the spring exerts on the diaphram. The fixed threshold model uses a calibrated spring and shim internally to regulate at what pressure it will open. This model is less easily adjusted. To adjust it, you replace the spring for one of different strength, or add/remove a shim which has the same effect.

Inside, there is a diaphram connected to a plunger which allows exhaust to be directed to the turbine blades on the Turbo. The hard line you refer to is the boost control line and it's function is to direct positive pressure (boost) to the diaphram on the side opposite the spring.

Once sufficient boost pressure is produced, the spring pressure is overcome and the plunger opens directing the exhaust away from the turbine and out through the exhaust system. This slows the turbo and reduces the boost. Once the boost pressure drops sufficiently, the spring pressure overcomes the boost pressure and the plunger closes allowing the turbo to spool up again.

A variety of issues can occur with these wastegates. The plunger, which lives in the exhaust stream can become clogged and fail to seal properly, this has the effect of only partially feeding the turbo. Or, it can stick in either the open or closed position, or anywhere in between, in which case you have either no boost, partial or runaway boost. Also, the diaphram can tear, rendering the wastegate totally ineffective at regulating boost. Finally, the spring can either break, or suffer fatigue, which result in only partial boost or no boost at all.

The fix is to rebuild the wastegate, either yourself (parts are available) or by a shop. A shop is preferable because they have the equipment necessary to recalibrate the wastegate. Hope this helps. Happy Motoring!...Jim'85TE

>> Edited by lotusguy on Tuesday 25th November 19:29

[cnh1990]

Yes that is correct that the 88 does not have a rod to adjust, my response was directed at a question from dictys who has an 89 SE. So the detailed test proceedures are geared for SE model and newer.

Calvin

[igreenrover]

Hi Guys

Finally got to look at the car last weekend…

When I put it on the ramps I could hear something knocking on / in the exhaust system and after further investigation it appeared to be coming from the Cat.

Anyway, I removed the exhaust back box and BPV only to find half of the Cat matrix jammed in the valve and blocking the exhaust. After removing this, and the rest of the matrix from the bottom of the Cat I have boost again. I think the cat overheated when I suffered ECM failure and this is why…

Anyway, the Cat appears to be constructed in two halves, with a primary and secondary matrix. The primary appears fine so I left it in there – any comments? I don’t think it’s a problem in the UK as it was not strictly required for emissions until the 90’s.

Gareth