I've finally sorted out the ignition problems in my 84, got a rebuilt computer and distributor over the summer, latest thing i did was get rapidfire plugs. i was having lots of trouble with the plugs fouling out, but these rapidfires work much better. My issue is, when i first start the car, it runs great, then after 30 or so seconds it gets really rough, then straightens out again aroud 150 or 160 farenheit. I started it cold with a test light on it and watched. As soon as it fired (my base timing is 10 degrees right now), the timing shot up off the scale like you would expect. After a few seconds, the timing started slowly coming down, all the way to the base timing. Thats when it started running rough. i had my Dad get in and bring the rpm up to about 1800, and it was still rough. suddenly while he was holding the rpm the timing shot back up way off the scale, it straightened out and the rpm jumped to well over 2000 w/o a throttle change. i checked EST and ESC per the manual , everything was normal. any ideas on what causes the timing advance to drop out when its cold?

 

wow... that's a real pain.

Do you have the helms manual? It might address this problem directly.

However, the rebuilt distributor might be the problem, or, the remanned computer....

base timing, I think, should be down around 6 degrees

 

There a number of things that can cause this.

My similar problem, years ago, turned out to be a faulty ECM. I identified it, after checking everything else, by swapping in a borrowed ECM that I knew was in good working order.

Easiest way to diagnose this is to hook up a real-time data logger, like Diacom, etc., then you can see if one of the sensors is out of range.

I suspect 02 or coolant temp sensors, but I'm not big on just changing parts in the "hope" of hitting on the malfunctioning one.

Jake

 

I would suspect the coolant temp sensor in the front of the manifold.
Do you have a scanner so you can see what temp this sensor is reading and compare it to the dash temperature indication? Note that the dash indication and the ecm use two separate temp sensors.

The alternative is the remove the sensor and test it in hot water with a digital ohm meter. The temp vs ohm charts are in the shop manual.. I can post them if required.

 

10 degrees is safe, just watch out for detonation. I run 10 degrees on premium fuel with no problems.

How many miles are on this motor? If you have over 100K on it, your timing chain needs to be replaced. Mine was so loose the motor was loping all over the place and idled like crap. Also couldn't keep it timed correctly. Replaced the timing chain, and now it idles much better, has more power, runs smoother, and the ignition timing sticks dead on.

It starts to run smoother at around 150 degrees because it's going into closed loop.

Are you getting any codes?

 

sorry i didnt fill u guys in on the details... the previous owner had replaced the engine with a 383 shortly before he passed away. his wife doesnt know much about cars so she wasnt much help in lettin me know what it had. it has iron heads but i dont know the casting #. The car just will not run at 6 degrees timing. it smokes and shakes at that low of a setting. ive had so much trouble the last couple years getting the timing right. i think when i had first gotten the car the dist was in a tooth off, since the balancer mark was way off the scale even in est bypass. getting the helms this year helped quite a bit, i didnt know to put it in so the rotor is between 1 and 8 at TDC.... now it seems to be in the right place. like i said though if i back the timing down anything under 8 it starts smokin and poppin. i think the higher linear speed of the piston at the same rpm to get through the longer stroke distance somewhat explains that. also the cf manifold must not help much with the closed out ports... the air must be slowing way down when it spills into the intake runner... i bet it needs the timing for power just to keep the air going into the chambers. also if it has a different cam thats confusing the computer too. anyway i was just wonderin if there were any known glitches in the 84 4+3 ecm in open loop mode... i had checked the manifold water temp sensor a while back with an ohmeter when the engine was cold, and the resistance was close to the book value. oh well at least its runnin pretty well warm. im thinkin about seein if anyone around here can extrude hone a cf manifold. im a little leary of the x-ram. well thanks for the help guys.

 

one more thing i forgot to mention guys. the car was running so badly from the time i got it in 2001 up to this year that the engine is full of carbon soot. (the coil had a hole burned through the side, and the square metal coil framing had melting marks adjacent to each plug tower, so i replaced distrib, coil cap and ecm.) the plugs still kept getting wet all summer till i got rapidfires a few weeks ago, now its running much better. anyway i stuck a q-tip into a cylinder and it came out looking like charcoal. literally, i mean solid black particles like .5mm diameter, plus loads of fine black ash. not sure of the best way to clean it out.... dont really want to go so far as to take the heads off now that i just got it runnin nice. it has a triple shot of lucas fuel treatment in the tank so thats probly makin the stuff start to come loose. oh well thanks guys

 

If it runs that poorly with the spec timing, I suspect the outer ring of the vibration damper may have moved, and you are getting incorrect reading from your timing light. You should verify your timing marks.

It sure would be nice to know more about that cam. Does the widow have any old receipts, or can she send you to whom ever put the engine together? Piston speed has nothing to do with your basic tuning problems. You are "over thinking" the situation. More "over thinking". As bad as a stock Crossfire manifold is for performance, it has nothing to do with your drive-ability problems.

The only people that can Extrude Hone anything thing, is Extrude Hone. I am aware of one guy that had his Crossfire intake Extrude Honed. AFTER it was ported, they charged him something like $700.00 for the job. For now, your need to get it running properly. THEN you can pull the manifold and port it yourself for a dramatic improvement in performance.

RACE ON!!!