BS: Car problem - any mechanics out there?

Subject: RE: BS: Car problem - any mechanics out there?
From: Claymore
Date: 18 May 10 - 08:40 PM

I have read all of the above and still think its part of the automatic choke system which unfortunately is part of the engines black box (very expensive).

To insure its not your wires, simply observe your engine at dusk. If its a wiring problem, the sparks will light up from the point of origin (hole in wire, bad radio resister on spark wire etc to the top of your head gasket. However such a hole in a wire etc. would only affect the performance of the engine, especially during idling and not starting. In addition if it was some form of electrical problem, the injectors would still be letting in gas which you could smell at the exhasut pipe after some of the cranking you describe.

Also you never said that if the vehicle did start up at one of the "middle points" was there a bang or sudden acceleration (hydrostatic lock on the injectors).

Once you have eliminated the elecrical possiblity then the only other case is the throttling of fuel as the third part, lack of O2 would only be cause by a super dirty air filter or an old fashioned throttle plate.

A quick test would be to have a friend attempt to start the car while you placed your hand over the air intake and removed it after a few revolutions or until the car started. This test would indicate a black box interface with both the injectors and the spark unit, as the pumping motion of the piston movement would suck in more fuel if your hand is acting like an old fashioned throttle plate.

If there is a spark she should fire right up, but at the end of the day you still have a black box problem, which might be solved at the local junk yard. Incidently some of the folks in a junk yard are the best mechanics in the business, and might be persuaded to wire it up for pin money

Subject: RE: BS: Car problem - any mechanics out there?
From: Bobert
Date: 18 May 10 - 09:50 PM

Well, Claymore, ol' buddy... That's exactly what I said except in fuel injection lingo... They don't have chokes... They have cold start valves that inject more fuel into cold engines... Same principle as a choke... I think it's faulty and shutting off too soon and that tyhe engine isn't warmed sufficiently before it shuts off... That's why it won't restart when it is just slightly warmed up... It thinks the engine is fully warmed up when it isn't and therefore is stravin' the engine when it's only slightly warmed up...

That's my call...

What the hell you up to, Claymore??? I played a private party in yer neck of the woods this past weekend... Didn't see you there...

b~

Subject: RE: BS: Car problem - any mechanics out there?
From: mousethief
Date: 19 May 10 - 01:38 AM

Also you never said that if the vehicle did start up at one of the "middle points" was there a bang or sudden acceleration (hydrostatic lock on the injectors).

No it does not. If it does start in the middle points (sometimes after I've cranked it three or four 5-10 second cranks separated by 10-20 seconds waiting) it sounds like normal.

A quick test would be to have a friend attempt to start the car while you placed your hand over the air intake and removed it after a few revolutions or until the car started. This test would indicate a black box interface with both the injectors and the spark unit, as the pumping motion of the piston movement would suck in more fuel if your hand is acting like an old fashioned throttle plate.

I don't understand what this means. I'm a car lightweight. I haven't worked on a car since my 1967 Mustang and it was much simpler, and had a carburetor.

Subject: RE: BS: Car problem - any mechanics out there?
From: Richard Bridge
Date: 19 May 10 - 02:11 AM

I'm itching to find out the answer when it is discovered - and at present everything points to some sort of enrichment device (not "choke" - those only exist on carburettor engines). But it could be an electronic control (part of or attached to the Engine Control Unit - many have one or a set of resistors to control signal voltages which cowboys can tamper with to provide more fuel if they have turned up the wastegate on a turbo - a disgression in this case but a fault with such a resistor COULD be the problem) fault, or a sensor fault providing the wrong signal to the ECU, or it could be an associated device (like the "radio suppression relay, which is not actually a radio suppression relay, on 7 and 9 series Volvos) or it could be something like the ancillary injector rail pressure (on early V6 Volvos with mechanically controlled injection there were three different injector rails, one for cold start, one for normal running and one for in between).

Subject: RE: BS: Car problem - any mechanics out there?
From: JohnInKansas
Date: 19 May 10 - 01:19 PM

The problem does suggest a fuel mixture error.

A component critical to fuel mixture that is somewhat prone to failure is the "oxygen sensor" that detects unburned fuel in the exhaust gas to tell the computer to make the mix leaner. (More air - less fuel.) Many recent vehicles have two oxy sensors, with one near the actual engine exhaust point and a second one nearer the catalytic converter outlet.

Since a richer mixture is needed for cold starting, the oxy sensor is likely to pick up an excess of fuel during starting. As the engine warms up and the mixture is "leaned" the excess has to be burned off, so the sensor actually lags the actual exhaust gas state as the mix leans, if a fully rich mixture was used for the cold start.

Residual "excess" on the sensor, when you try to start a warm engine, may make the computer think the mix is too rich, so it provides a very lean mix to the engine, with insufficient fuel for the restart.

If the engine runs long enough to "purge" the oxy sensor so that it gives a correct reading for the current state of the engine, the mix will be right for starting. If the engine didn't run long enough to clean up the excess from the last cold start, the mix will be too lean for re-starting.

A good sensor should clean up very quickly, but one that's been in service for a while may have a much slower response. Even a sensor that's gone completely "dead" probably won't prevent starting under most conditions, and a dead or dying sensor is usually seen just as a degraded performance while the engine is running. The sensor also can be "killed" rather quickly by fuel contaminated with anything that doesn't "burn out" quickly, with even small amounts of leaded fuel being a most common cause before it was mostly eliminated from the market. Some aftermarket "fuel additives" still available can have very negative effects.

Exhaust system leaks, or clogging, can significantly affect how quickly the sensor cleans up, and how closely it follows actual mix conditions. Exhaust line problems that persist for too long can actually cause permanent sensor failure. An inefficient (worn out) catalytic converter might allow the secondary oxy sensor to call for leaner mix.

Some engine computers from around the era of the vehicle in question did not record an error that directly indicates oxy sensor failure, although I can't say whether that's the case with the specific vehicle involved. The diagnostic test for sensor condition is a simple resistance (any VOM/multimeter) check, but resistance values have to be matched to actual sensor temperature and you'd need specs for the specific sensor on the vehicle.

This is only one of many possibilities; but it's one commonly mis-diagnosed and ignored around the time that the vehicle in question was new. (New oxy sensor - $20, "carburetor rebuild" or mixture control module replace - $400, hence a bit of bias in what the mechanic tried first)

John

Subject: RE: BS: Car problem - any mechanics out there?
From: Richard Bridge
Date: 19 May 10 - 06:34 PM

That seems plausible John - but -


I cannot say for a Honda, but the equivalent sensor on 7 and 9 Volvos (which they called the "Lambda sensor") if faulty would have given a code readout.

Subject: RE: BS: Car problem - any mechanics out there?
From: JohnInKansas
Date: 19 May 10 - 11:42 PM

The information available from the computers has varied a lot from one vehicle to the next. Whether the mechanic who plugs in to read the information will know what it means probably (in most places) varies a lot more.

Most of the diagnostic stuff does prove helpful for "standard failures," but for anything "intermittent" the codes are mostly useless, and GM at least gave multiple warnings about not believing the computer under many circumstances - or at least they did a few years back.

There are lots of other reasonably common failure points that could contribute to the problem at hand; but like for computer problems, many are quite difficult to diagnose without "hands on" the machinery. There are too many likely "solutions" to know which ONE is right.

John

Subject: RE: BS: Car problem - any mechanics out there?
From: ragdall
Date: 20 May 10 - 02:02 AM

I may be wrong but surely a 1978 Fairmont will have carburettors rather than electronically controlled fuel injection, so the diagnosis process may be rather different from the OP's Honda.

You're right. My car will be getting a carburetor transplant, Friday. It'll cost my entire pension for this month. Not sure about putting a new carb into a 32 year old car. I hope it won't reject it?   

rags