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MYRONB
User Rank
Gold
Re: Diagnosis of Engine Lacking Power
MYRONB   5/21/2012 4:03:11 PM
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To xti, et al;

Since other factors, timing, ignition, etc., seem OK, I suspect the problem may be in the fuel system.  If this is a fuel injection vehicle, I would check the pressure in the injector fuel rails.  If low or non-existent, I would check to see if the in-tank pump is running or the in-tank filter is clogged; remember, if the engine doesn't start, the fuel pump will run only a few seconds.  These are not easy to check, I know.

If carbureted, check for (usually mechanical) fuel pump pressure and also the small filter at the fuel inlet to the carburetor.  Also, for either fuel system, check the fuel tank evaporative emission controls and fuel tank venting.  Without venting the tank won't flow.  I would also check the engine air filter as well.  And, oh yes, you did check to see if there was fuel in the tank, right??

Best regards to all, Myron Boyajian

 

Critic
User Rank
Platinum
Diagnosis of Engine Lacking Power
Critic   5/21/2012 9:48:48 AM
NO RATINGS
xti:  the gradual loss of power tells me that there is probably an exhaust restriction, such as a clogged catalytic converter.  However, I would start by running a comprssion test, and if the compression is OK, then check for exhaust and intake-air restrictions.  If compression and airflow are good, then the next step would be to check the air/fuel ratio under power.  Ignition timing could also be a concern, and should be checked as well (probably before the fuel mixture) at all RPMs.

GlennA
User Rank
Gold
Re: Engine issues - tangent
GlennA   5/21/2012 8:30:41 AM
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xti;  I have a theory, but it is not Ann Elk.  I will wait to see if someone else weighs in before I post it - to give others a chance also.

GlennA
User Rank
Gold
Re: Overlooking the obvious = No
GlennA   5/21/2012 8:28:14 AM
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MyDesign;  It's always easy when it is someone else's probelm.  Read xti's post on the Monte Carlo problem and have a crack at that - before knowing what the answer is.

GlennA
User Rank
Gold
Re: Monday morning quarterbacking
GlennA   5/21/2012 8:25:07 AM
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MyronB;  So what is your suggestion to xti's Monte Carlo problem ?

MYRONB
User Rank
Gold
Re: Monday morning quarterbacking
MYRONB   5/20/2012 1:52:02 AM
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To Glenn A:

Good question, but recall that a test for vibration takes but a few seconds, so starting with a cold engine should not cause any problem at all.  Keep in mind that dragsters (top-fuel class cars running nitromethane fuel and superchargers putting out several thousand horsepower) use no coolant at all.  Yes, I know they only need to run for the burn-out, staging, and a 5-second race, but as I said, testing for vibration only needs a few seconds.

Regards,  Myron Boyajian

 

 

xti
User Rank
Iron
Re: Engine issues - tangent
xti   5/18/2012 12:15:20 PM
NO RATINGS
Timing is good, mechanical advance works as expected. Ignition system checks out OK. (MSD 6A's will easily fire plugs gapped at .150 - even if they're immersed in oil.)

- PS if you ever work on a car that has an MSD ignition - be EXTREMELY careful. NEVER go near the plug wires with the engine running; and NEVER even go near the PRIMARY side of the ignition unless the battery is disconnected. Experience is speaking.

Brakes are fine. Parking brake is fine. Car rolls very easily.

Engine does not miss, backfire, or run rough. Just has no power. Starts easily hot or cold. No strange noises in the engine, no vibrations. Oil pressure is fine. Temp is fine.

 

So where are all the people that were telling us how they could have found the missing bearing in 15 minutes, and how dumb the mechanics were to be changing all those parts?

C'mon guys - step up and tell us how to fix the Monte Carlo. No wild guesses - only a methodical, reasoned approach is allowed.

I will even give you a hint. Three things that troubleshooters often seem to ignore in favour of a purely technical approach. What, When, and Where. But you have to ask the right questions. Customers rarely recognize that something they did might have caused a problem. Oops, did I just see a cat run out of that bag?

If nobody seems to be getting warm, I'll define exactly what I mean by those terms.

GlennA - thanks for playing along. At least someone has big enough, er, "dual, low-hanging, spheroid" objects to step into the fray.

Rob Spiegel
User Rank
Blogger
Re: Engine issues - tangent
Rob Spiegel   5/18/2012 12:14:52 PM
NO RATINGS
You're right. I misunderstood that, GlennA. But you did end up answering my question. The engine had to die before they crankshaft problem could be identified.

GlennA
User Rank
Gold
Re: Engine issues - tangent
GlennA   5/18/2012 9:15:43 AM
NO RATINGS
Connect the ignition to the scope / analyzer = check the timing adavance.  You may not have enough advance under load.  Check the brakes = are the brakes, especially the parking brake, dragging ?

xti
User Rank
Iron
Re: Engine issues - tangent
xti   5/18/2012 3:47:33 AM
NO RATINGS
GlennA

The engine revs OK in neutral. Just doesn't have any power under load. Idles fine, too.

Fuel pressure is fine & doesn't drop off under load. Filter in front of QJet carb was changed when cam was changed, but has a bypass spring anyway.

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