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mswest68

88 Turbo - Complete loss of power at around 4300 RPM

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I'm not sure if this is turbo related or a failure in the engine management system.  Car operates fine at idle, through normal acceleration, up until I hit about 4200 RPM. At that time the engine completely cuts out with a violent loss of power.  When this happens I naturally take my foot off the accelerator, at which time the car then drops in rpm and again operates normally until high rpms are reached again.  

Could it be a bad overboost switch, or wastegate failure?

Additional Info.. may be related... my boost gauge never moves and and do not hear the blow off valve operating when driving. 

Any help trouble shooting would be greatly appreciated. 

Edited by mswest68

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Wastegate not opening, engine going to overboost, resulting in fuel or spark cut would the obvious guess, but if you are showing no boost that's weird.   Unless the boost  plumbing to the wastegate also feeds your boost gauge. Check the plumbing, check your boost gauge with another gauge and maybe pull the wastegate cap and make sure you have  movement of the valve if you are getting boost.

I'm not familiar with the 88 engine management though, others should chime in soon.....

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Sounds like rev limiter cutting the spark, does it not?

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Check the distributer wires for breakdown, it is more usual at around 3500revs though. As the advance kicks in the wire streches and breaks. 

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Sounds like fuel cut. The ecu protecting the engine. I have no experience of the fuel injected cars so can't really offer any help. :)

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Engine Overspeed Module. Look for it on the left side of the coil 'box' (rear engine wall).  Does the part number start with an A or B?

 

PS:  Yes it DOES work by cutting power to the fuel pumps, can be a violent experience.

 

 

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While taking a thorough look under the car today, I noticed the exhaust back pressure valve (EBPV) is not physically connected to the corresponding lever on the exhaust pipe.  The valve and associated spring look to be in bad shape - probably broke away from the lever.  Though, I'm not sure this is what's causing my problem.  

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That is not a valid Lotus part number for the EOM. You are looking for a number more like 'A082M6374F' or better, 'B082M6375F'.

 

BUT, you may be onto something with the EBPV (potato valve). Many owners wired those open so verify that the valve is in the 'correct' (open) position.  JAE Parts in the USA sells a spacer to eliminate the valve.

Edited by CarBuff

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I think my problem is in the wastegate, so I'm going to try my luck at rebuilding the assembly, but nothing is ever easy on this car.  I'm stumped.. I can't figure out how to get the wastegate off the manifold - there's just no accessing the bolt nearest the sump.  I then tried to drop the wastgate while still on the adapter manifold.  no luck there either - again can't get to the nuts closest to the motor.  

Does anybody have any experience with this?  Any advise would be great. thanks!

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You can disassemble the wastegate in place, but mind the compressed spring under the hat. You can't get to the valve seat, but you can check the diaphragm, and perhaps un-stick a sticky valve. Someone clever mentioned removing some  of the screws and replacing with zip ties through the holes before removing the rest of the screws. 

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Might be worth putting a manual pressure gauge on to see what, if any, boost you have.

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Another thought upon re-reading the Original Posting:

 

There is no factory Blow Off Valve on an '88. Did a previous owner fit one? Might be a good idea to block it from actuating during your troubleshooting. I've seen a few BOVs that have stuck and malfunctioned.

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Are you sure it's the wastegate? The symptoms somehow don't seem right to me, but I stand corrected as always.

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You can test the wastegate by applying pressure with a compressor and a gauge, to see if and when it opens. If it doesn't open, the ECU will cut fuel and/or spark. That would cause a sudden loss of power. If the wastegate would open to early, you'd still have some power as air is still getting in, just not under boost. Provided you have spark and fuel.

Filip

 

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7 hours ago, Escape said:

 If it doesn't open, the ECU will cut fuel and/or spark. That would cause a sudden loss of power. 

It's an '88 turbo, does it have an ECU?

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So, in light of the many other things I should probably address on the motor (timing belt, accy belts, oil links, etc.) and because I really want to remove and inspect the exhaust, I decided to yank the lump out.  Having never done this before, it took me about 6 hrs, but well worth it.  Now I can properly clean everything up, replace all the belts, seals, hoses, etc. and hopefully fit a functioning exhaust.   

Speaking of the exhaust system, I can't seem to find anyone that sells a replacement silencer and other parts.  Considering the Alunox system.  I've emailed the company twice, but haven't heard back.  any recommendations out there for replacing the whole exhaust system with a higher performance aftermarket m,m?

Matt

20190217_150052.jpg

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Be careful when sourcing exhaust systems from the UK. Many will differ from USA spec. (eg, the tailpipe exits at the left side, or the catalyst/EBPV is different, or the piping diameter is different)

 

The factory Bosch (Langford) exhaust is a 3" system. And, it is stainless steel. Sounds good. 💪

 

While you have the drivetrain out, fit a heavy-duty input shaft circlip (available from JAE or Harry Martens) to the transmission...

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At this point, I couldn't resist doing a complete engine rebuild. I'll provide updates as I can. Currently, the motor is disassembled and at the machine shop getting a 3 angle valve job, crank polishing, and balancing.  I'll be removing the external wastegate system and going with a new turbo with internal wastegate and Alunox SS exhaust manifold and fitting kit.  I hope to start reassembly this week.

 

 

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