Hello:

1986 Coupe..stock motor...PCM 4Less tune
Removed smog pump and related components

In the past couple of weeks i have developed a poor cold start situation (outside temp around 50+ degrees). Seems like when you have a choke problem on the older vehicles.
The car cranks longer than usual (5-7secs) after sitting over night or an extended period of time.
Then when it does start it seems like it is barely catching and runs poorly...chugging and sputtering for the first while ..i have to give it throttle to keep it running sometimes...until warmed up and then it runs just perfect.

--no codes
--removed and cleaned throttle body
--deleted air pump and components when i did the waterpump 2 mnths ago
--new IAC..8mnths
--new water pump..Edelbrock..2mnths
--new performance thermostat 180..2 mnths
--new TPS...2 MNTHS
--new FIC 24LB injectors...1200 miles ago
--new MAF power and burn-off relays..8 mnths ago
--new fuel filter 1800 miles ago
--new fuel pump 1800 miles ago
--timing at 6 BTDC
--swapped in a known working ECM...no change
--swapped in a spare MAF sensor...no change in starts.
--unplug the maf while at idle and the car gasped for air..sputtered the the idle leveled out again
--pulled a few spark plugs and they all looked fairly normal...whitish/brown...no concerns
--tested a new Coolant temp sensor by just plugging it in on a cold engine and starting car...no change
--new cold start switch at the front of manifold..1 year
--Fuel pressure at rail with key on is 42lbs
--no fuel odor in the line to the Fuel pressure regulator
--Manifold pressure is 19lbs...does that mean there are zero vacuum leaks??
--Datamaster scan show nothing out of the ordinary...by the time it goes into closed loop, the car is running great.
--also noticed recently too that warm/hot restarts take about 2 secs where before this it would fire instantly when up to operating temperature.

--does the EGR valve play any part when the car is started??

I would appreciate all your thoughts on comments about this issue

Sorry for the long thread but i was trying to be thorough

Ray

 

Cold Start injector? Is it functioning or was it tuned out? The 89 uses the same ECM you do but does not have a 9th injector.

 

not tuned out of the bin....im using $32 bin

I could unplug it and see if it makes any difference.

I didn't think that injector came into play at temperatures of 50+ degrees?

do you suggest i unplug it and try it with the 89 ARAP bin?

 

The cold start injector switch only works while cranking. It has a heating element inside it and times out after 8 seconds. It will not function if the coolant is over 95 degrees F.

 

Last Night...Changed the CHIP to the 1989 ARAP...unplugged the CSI connector at the injector...no change...actually seemed liked it cranked over longer before catching? still ran choppy till warmed up.

This morning...OHMed all the injectors cold...seemed well within specs 14.2 to 14.4...CSI ohmed at 4.0.

Put the ECM back to the way it was with custom $32 bin and reconnected the cold start injector (assumed working)

any ideas??? anyone

Thanks

 

8 new ACDelco plugs did not help either...didn't hurt anything...

Anyways,,,,always wanted to change out those Champions that the PO had in there a few years ago

 

My buddy thinks it is my fuel pump going bad. We took the air coupler off and sprayed a shot of starter fluid and it fired up and continued to run. It is only if it sits for a long time that is wont start. Is the fuel draining out of the lines thus the bad fuel pump problem. How long does it take to change out a fuel pump in my 1988 C4 ? Does it sound like it is the fuel pump ?

 

Put the gauge back on the fuel rail. Key on for 2 seconds-off, read pressure. Should be pretty close to 40 or so. Sounds like the fuel is leaking back down after shut off for a while like overnite. My sons Avalanche does the same thing but I will key on/off cycle 3-4 times and it cranks fine. His mechanic is replacing the fuel pump as we speak. I am out of town, my sons bad luck, my good fortune, lol. I know who would be doing that job for free.

 

whats the fuel pressure at idle and as rpm is rapidly increased? as in floor it..?

The fuel pressure gauge tells everything that you need to know about the fuel system by observing the way the needle behaves under a variety of conditions.

If you think it thru...you are watching fuel under tension thats being used and replaced. As use increases, does the gauge indicate that supply keeps up with usage?What about replenishment? A dip is normal but the length of time for the tension to recover is critical.

Keeping the gauge on the rails for a night and writing down the system pressure every hour (for at least the first 5-6) to get a picture of the system integrity is very helpful. Hint...if it don;t hold at least 30 psi after 1 hour then its too loose and leaking/bleeding off. A good pump/system should hold pressure all night and have 10 psi for your viewing pleasure with your first cup.....A system that drains itself and has to completely refill and repressurize will be hard to start cold, slow to start because even though it self primes there WILL be voids in the injectors that cannot go away until liquid is allowed to pass thru as each injector cycles a few times (aka cranking time).
Don;t use starting fluid on these engines. It fractures piston skirts and ring glans...Starting fluid is for diesel engines.

 

Yeah, what Lee said

 

Not sure if you guys are addressing my original issue or the problems that C4in mesa stated.

Anyways...when i measured my fuel pressure it was 42lb at the rail with key on.
When i was cranking the engine over it dropped to about 38 and held at 38 when the motor was at idle.

I observed leakdown for about 2 hrs and pressure dropped from 42 to about 35lbs after that time...i dont think i have any leakdown issues but will monitor it overnight and try to record a few intervals and post what the pressure id in the A.M.

btw...still having the "barely catching...sputtering cold starts" perfect after its warmed up...like 3-4 minutes

 

My issue is th same as raiderz meaning that after I get it started my troubles are over unless it sits for awhile. I have not yet used a gauge to test fuel pressure. I found a pump for $100. I looked in my service manual with no luck telling me if it is in the tank or outside the tank ? How many hours to do this job. I do not do any work on the car. I wish I could ! Sadly I lack the patience, garage and tools ! My mechanic is good but I would like to hear from you guys on how long the job will take should I have to replace the fuel pump.

 

Fuel pump re/re very simple job to do.
Pump inside the tank
takes 1hr with a couple of pops...ur mechanic probably wont be drinking any so it should take him 45mins ...tops.

There are a ton of write-ups on the forum about the procedure...Search

 

15 hour Fuel pressure reading as follows:

5:30pm 42lb
6:30 34lb
7:25 29lb
8:30 24lb
9:25 22lb
10:30 20lb

9:00A.M. 8lb

Doesn't seem like i have any fuel pressure issues....back to testing some more sensors / wiring i guess

 

Thanks raiderz have a great Memorial Day !

 

Yessir....thats right about what it should be.
Well, the next thing to question in the fuel system would be the injectors themselves...
Even IF they pass OhMs testing all that indicates is that the injs solenoid /coil is ok. These on-car test do not speak to the quality or ability of the injector to spray fuel. Knowing these things as we all do, its one of the better (safe) bets to assume that the injectors are BAD,. just by way of history and age, if nothing else.
They have baskets, screens and nozzels that get clogged and ruin the spray in the intake runner. They will dispense droplets instead of mist and that makes for a hard to start engine. If these are the stock injectors...its time. For $200 you can hardly go wrong.

 

....New rebuilt Bosch3 24 lbs from FIC about 1200 miles on them as in my first post. Not a likely culprit...but you never know?

Im leaning towards a sensor being the issue. I tested the CTS wiring with key on and get 4.98volts from the ECM...i swapped out a new coolant temp sensor not installed...just plugged in) started the car..no change...i might try another new coolant sensor in the same manner...it really feels like the old choke days when u start it cold?

 

Got home tonight...still had the gauge on the car from last night..and all day...went to unhook the gauge at about 8:00pm and the gauge was reading 18lbs??

WTF...when i left for work this morning at 9am it was 8lbs...nobody touched the car in all that time...how does the pressure at the rail increase like that on its own??

It was an extremely hot day here ...100 degrees F in my garage..does the temperature have anything to do with the pressure increase??

Freaked me out!

 

could be vapor pressure from fuel expanding in the rails in the heat (like gas cans expand if you don't open the vent valve), nothing to worry about IMO. Your fuel tank is vented to allow for expansion.

 

I was hoping it was something like that....don't need another issue until i can the starting problem straightened out.......

I tried another new coolant temperature sensor swap this afternoon...same results....extended cranking..barely catches when it does fire...have to give it throttle to smoothen it out and idles choppy for 2-3 mins then its okay....runs perfect after 5mins in this heat.

Its gotta be a sensor because it runs perfect when warmed up....which one?
Any other sensor on this L98 come into play for start up?