How to Troubleshoot Your Turbo

A turbo charged mercury capri in 1991
A turbo charged mercury capri in 1991
How a turbo works
How a turbo works
What the turbo looks like
What the turbo looks like

Troubleshooting a turbocharger

All turbocharged engines since the 1960s are generally the same when it comes to diagnosing why they are or are not working. They comprise of a:

· Actuator, which is a spring loaded diaphragm device that sense and controls the pressure in the compressor discharge

· Compressor, which is a centrifugal radial outflow type

· Turbine, which drives the compressor and is a radial inflow type

· Wastegate, which allows a portion of the exhaust gas to bypass the turbine wheel limiting compressor speed to limit boost pressure. Boost itself is controlled by the Wastegate, which closes to optimize vehicle performance. It opens to limit boost when the maximum limit is reached.

· Center housing, which supports the bearings, compressor, turbine and oil seals

The turbocharger is driven by waste exhaust gases forced through an exhaust housing onto a turbine wheel. The turbine wheel is connected by a common shaft to a compressor wheel so that both wheels rotate simultaneously when the exhaust gases hit the turbine wheel. Rotation of the turbo assembly compresses the intake air routed through a compressor housing, forcing the compressed air into the engine’s cylinders. The increased amount of air forced into the engine creates more power than a similarly sized non-turbocharged engine and power similar to a larger, non-turbocharged engine. For comparison, a non turbo engine in a 1994 Mercury Capri has 100 hp, while the XR2 Turbo model, has 132 hp, using the same 4 cyl. Engine. The difference to a driver is substantial. The non-turbo engine is underpowered and has no get up and go, while the turbo is quite the opposite. In 1966, Chevy sold their rear engine Corvair Corsa Turbo which created 180 hp, compare it to the standard Monza model that had 110 hp. One downside to a turbocharger, is the superheating of the intake air. Since the turbine must be run by hot exhaust gasses, the heat transfers via conduction to the compressor. The compressor becomes superheated, and therefore heats the incoming air to the engine. The other main con of a turbocharger is something called turbo-lag. Turbo-lag is the time it takes for the turbo to spool up and produce power. Since an engine does not create large amounts of exhaust in low RPMs, the turbo creates small amounts of boost, and must have time to gain rotational inertia from the exhaust. The Turbos of the 60s and 70s are known for their finicky operation, or, everything had to be perfect in synch and to spec to avoid problems. They required frequent tweaking. Turbos from the 80s on, are much more reliable. If maintained, they will last 100,000 miles before replacement.

TROUBLESHOOTING CHART

PROBLEM

DIAGNOSIS CHECK

 

No Boost

Compressor inlet hose collapsed, Compressor outlet to throttle body hose leaking, turbo or compressor wheel is damaged, turbo bearings have seized, wastegate is stuck open, clogged air cleaner, clogged air passage upstream of compressor

Fix

Tighten hoses, replace turbocharger, open wastegate, replace air cleaner, unclog air passages

Lack of Power

Bad engine compression, incorrect valve timing or clearance, incorrect ignition timing, clogged air cleaner or hose restriction upstream from compressor, oxygen sensor bad, volume of air flow incorrect

Do compression check, correct timing and readjust valves, find air flow restriction, test oxygen sensor

Detonation with No Boost

Low grade fuel, ignition timing is too far advanced

Add higher octane to fuel or drain and replace, correct timing to spec.

Detonation with Normal Boost

Same as no boost and: insufficient fuel supply, low fuel pressure, bad oxygen sensor, engine overheating, oil leaking into compressor from turbo, Valve seals leaking oil

Same

Excessive Fuel Consumption (black exhaust smoke)

Engine needs tuneup, high fuel pressure, fuel line plugged, injectors are leaking, oxygen sensor bad

Tuneup, test for fuel pressure in line and clogs, install new injectors, test oxygen sensor

Excessive Oil Consumption (blue, gray or white smoke)

Incorrect oil type, clogged air cleaner or hose restriction upstream from compressor, PCV malfunctions, Oxygen sensor bad,

Noise or Vibration

Leaks at turbocharger inlet and outlet, foreign object damage to turbine or compressor blade, turbine bearings failed

Replace turbocharger

High Boost

Wastegate is not functioning, leak in exhaust system before muffler, leak in wastegate activator to compressor

If exhaust is smoky

Check compressor outlet for oil, check compressor inlet for oil.

If compressor outlet is not oily, check turbine outlet for oil.

If oil is present, Turbo is OK, check PCV system for clogs.

If oil is found, it is an internal engine issue. If it is not found in turbine, Turbo is OK, smoke is from car engine.

If compressor inlet is not oily, check for restriction in turbo oil supply tube.

Repair restriction if found. If none is found, check for restriction in the turbo oil return tube. Remove restriction if found, if now, replace turbocharger.

Wastegate- check diaphragm

Remove actuator diaphragm hose at diaphragm. Connect pressure diagnostic gauge to diaphragm inlet. Apply recommended air pressure to diaphragm.

Actuator rod should move, if no, replace turbocharger.

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Comments 19 comments

capri xr2 4 years ago

why do you have to replace the turbo if only the actuator diaphragm is broken?


Vinsanity100 profile image

Vinsanity100 4 years ago from Michigan

This a very useful article. I plan on getting a turbocharger for my car this coming summer.


perrya profile image

perrya 4 years ago Author

My 91 merc Capri has a turbo. When it went out, I simply lost power and could barely crawl. since there was no excessive smoke, I knew the turbo did not go out. When I popped the hood, the hose had come off. I have talked to others whose turbo went out-tons of smoke-$3000 to fix/


Kits 4 years ago

Hi guys my 92 Capri turbo cuts out when boost kicks in. Like for instance when driving up hill turbo starts spooling and when u need it to pull it just cuts out. I've checked everything and is all good.

Umm is there anything like a restricter in the engine bay when boosting it?

Cheers.


Kits 4 years ago

It's a 91 merc Capri turbo


perrya profile image

perrya 4 years ago Author

how about small vacuum leaks anywhere? My 06 VW, with turbo, did this. I had no boost going uphills. It was a small slit in the rubber hose that was a 5 min fix. Any leak may cause it. These can be VERY hard to locate and time consuming.


Kits 4 years ago

So you think that there is no restricter in the engine bay and it has to be a leak somewhere?


Alan 3 years ago

Help my golf turbo has no boost still running vaccum but poors white smoke any suggestions


perrya profile image

perrya 3 years ago Author

defective wastegate?


Alan 3 years ago

Wastgate seems ok not stuck open and its white and bluey smoke thanks


perrya profile image

perrya 3 years ago Author

well, in my experience, when the turbo goes out, lots of black smoke comes out. Sorry.


Jane 2 years ago

I have a 1994 Capri and the turbo has been bypassed prior to me getting the car. Any suggestions on the first steps to check its functionality? Several hoses seem to be missing, any recommendations for purchasing them?


perrya profile image

perrya 2 years ago Author

Bypassed? Hmm, how does the car even run? The turbo model and the non-turbo model are different setups. The turbo model will barely run if the hoses are not connected or if the turbo is bad. Does the car run normally?


Jane 2 years ago

Yes, the car runs. It is currently being worked on since the transmission shifter stabilizer bar broke and I just found a replacement. While it is being worked on, I have decided to see if it would be possible to get the turbo going again.


perrya profile image

perrya 2 years ago Author

I guess by runs I mean, can you drive and accelerate the car? if so, maybe your turbo is fine and the hoses missing are not related to the turbo operation.


Jane 2 years ago

The car is drivable and able to accelerate; it is just very slow to get going.


perrya profile image

perrya 2 years ago Author

well, when my hose from the intake slipped off while driving, the car suddenly lost acceleration and while it ran, it could not go faster than 10 mph, so I pulled into a parking lost. I thought the turbo had gone bad. I was able to limp home at no more than 15 mph. The disconnected hose (2-3 inch diameter) was reattached and it ran great. without seeing a photo of your engine area, hard to tell you much.


Jane 2 years ago

I am able to get to freeway speeds. Just lack any quick acceleration. Is there anyways to upload a photo on here?


perrya profile image

perrya 2 years ago Author

Even with a turbo, the Capri is not fast to accelerate. It is FAR faster than a non-turbo, which is horribly slow from a stop. If you can get to hwy speeds, everything must be ok with the turbo. A turbo is either good or bad and you would hardly be able to drive if the turbo was bad.

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