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RX saga continues


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13 replies to this topic

#1 RedRX

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Posted 05 December 2003 - 06:59 AM

Slowly eliminating potential causes for the running problems - said problems being: sudden choking after engine has reached operating temp (ie - by the end of the street loses all power for a few seconds), constantly missing at cruise, gets smoother during acceleration, rich running, NO power right off idle (ie AC causes a stall even after hot-wiring the idle-up solenoid) and easy to stall at low revs. When she is wound up (2000-3000rpm) she will pull right past 6000, but always feels like something is holding her back. I KNOW this engine has MUCH more to give - built up by rally mechanics - hi-tensile head bolts, BIG cams (which I know affects the bottom end), and god only knows what head-work. The thing is it has been transplanted into this car with its standard running gear and computer.

So far i have fixed and checked the aux air valve, the EGR valve, cleaned out the disty, tested the temp sensor (the resistence varies with temp, and it gets 5 volts), the knock sensor works (even tho its only a single wire job when it should be the earlier 2-wire - I tested it SKIP, and wow, it DOES actually knock back the timing). Fuel pump has had output and pressure checked, I pulled all the lifters and freed and cleaned and primed them. Phew! I know i need a decent exhaust but there is an intermittency to the problem so it cant just be a clogged cat. O2 sensor is new and seems to work.

DAMN DAMN DAMN - anyone have a clue? I want the girl to sing as she should.:banghead:

#2 Skip

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Posted 05 December 2003 - 10:46 AM

Sorry Red, I know we must have talked by the reference.
I can't remember what year/fuel system you have.

IF it is a hot wire MAF system, have you swapped ignition amplifiers?

Have you any where to get another MAF unit, this unit sounds highly suspect after all you have outlined.

That baby should fly


#3 RedRX

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Posted 05 December 2003 - 10:24 PM

Its 86 Skip, with flapper AFM, and breakerless disty with separate knock control unit. You replied to a post i made about the single vs twin wire knock sensor. Supposed to be twin wire for this model but i have single wire installed - I tested with timing light and it DOES work - dunno if it's false-alarming tho - i just know it winds back timing when i tap near the sensor with a big screw-driver. I know this problem has to be in the control system somewhere cos the engine was rebuilt only about 500-1000km ago and built to take WAY more boost and revs than i give it. Just this damn missing and choking - geez could even be as simple as a faulty plug or lead, but they are new.

#4 Skip

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Posted 06 December 2003 - 08:40 AM

Red, sure sounds now like it is MAF related. If the vane (i.e. flapper door) is hanging (not moving open/closed in concert with the air flow)- it will do what you say.
Can you borrow one? Atleast take it off and feel it swing open and closed. Many people have been known to mess with the return spring in these to "fattin' " the mixture. Maybe the return spring is sprung. Hope this helps


#5 RedRX

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Posted 07 December 2003 - 01:28 AM

I have pulled and cleaned flapper and checked the internals under the glued cover - clean - and flapper is free and spring works
not checked outputs yet tho
need a decent meter

#6 josh long

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Posted 07 December 2003 - 02:44 AM

has this thing run well ever since rebuild? seems odd but have you checked compression? timing belts? dist timing? plug leads swapped? I have at one time or another run into one of these. I also had a cam follower fall off as I was putting one cam case and it took me for ever to find it...........:o

is the ecu known good?

well I'm sure much of this is redundant but give it a try.

Josh

#7 calebz

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Posted 07 December 2003 - 03:35 AM

Any Error codes?

I have a spare 85-86 MAF, but shipping would be a killer...

#8 RedRX

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Posted 07 December 2003 - 08:37 AM

JOsh, Skip and all. The fact that the problem comes and goes leads me to think that there is nothing structually wrong with the engine. The odd times she can run sweet. Interestingly - she runs much rougher with the headlights on; bad earth on the coil? or even a dodgy coil (I thought a bad coil was just that -BAD- not something that caused an intermittent problem.

PS - when using a timing light, is it normal for the strobe to flash at an intermittent rate? ie not firing every ignition cycle? I'm wondering if the leads are right resistance.

#9 RedRX

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Posted 07 December 2003 - 08:40 AM

Hmmm - let me clarify that last question. Does the fact that the timing light misses the odd ignition pulse mean that the PLUG is not firing either? or just that the timing-light pick-up via the clamp to the cable can only catch pulses of a certain strength.

#10 Skip

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Posted 07 December 2003 - 09:07 AM

Red, there have been quite a few posts relating to the flapper door ignition sytem and problems there in.
The intermitant strobe flash of the timing light could be a sign the ingitor in the disty is going or the knock control unit is supressing the spark voltage. What does the spark off the coil wire when cranking look like?
Have you checked the connections on the ends of the fusible links lately? Tha alternater output goes through the link closest to the strut tower, I say this in reference to the remark about the headlights. If we are loosing some charging juice possibly the coil primeray is not seeing the voltage it needs.
Your coil does not have the ignition amplifier on it's bracket so it does not need to be earthed.
This is not ruling out a faulty ground connection somewhere.
On hot wire cars the dash ground is under the intake manifold bolt just behind the upper rad hose connection, another important ground point is the screw by the battery in the rad. core support.
These intermittant problems can certianly be buggers to track down.


#11 RedRX

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Posted 07 December 2003 - 11:42 AM

Thanx Skip - your info is ALWAYS helpful. I'll keep you posted.

#12 bushbasher

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Posted 07 December 2003 - 04:48 PM

can't you just disconnect the knock sensor to see if that is the cause. I thought they were just a trigger, and only send a signal when there is knocking.

#13 RedRX

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Posted 08 December 2003 - 04:59 AM

Have done that bushbashr - still spits and farts. Not game to give it a GOOD run without knock-sensor tho :rolleyes:

#14 RedRX

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Posted 08 December 2003 - 05:00 AM

PS - from what i have read the knock-sensing apparatus is an arcane device with devious signals and mucho filtering to make sense of said signals.




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