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95 Chevy cranks excessively before starting

 
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n01tk



Joined: 23 Apr 2011
Posts: 39
Location: Nova Scotia Canada

PostPosted: Mon Aug 27, 2012 6:00 am    Post subject: 95 Chevy cranks excessively before starting Reply with quote

My C3500 will not lite up quickly after sitting ( 24hrs). I installed a new fuel filter, pump, lines and TBI ( rebuilt) This truck has the long fuel pump run time (~20 secs) to ensure vapour lock doesn't occur. I installed a fuel pressure gauge and get 11 psi ( gauge cal. checked). The gauge stays steady when increasing trottle. Installed a node light on injectors and both are pulsing when truck is cranking. Looked down tbi troat of the TBI and could see fuel in intake manifold. Turned my attention to spark. Repaced coil. Checked output, above 40,000 volts. Wires, cap, plugs and rotor button replaced < 1,000 mile ago. At that time removed ign. module, cleaned grounds and replaced module with thermal conductive grease applied.
This truck runs very smoothly when it does start and goes into closed loop when temp is achieved. Checked TPS and ECT sensors, both appear to be OK. The IAC counts are 35, which indicate no vacum leaks.
I am now wondering if the fuel is being sucked into the cylinders, but my vac appears to be OK? Running out of ideas. All help greatly appreciated
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n01tk



Joined: 23 Apr 2011
Posts: 39
Location: Nova Scotia Canada

PostPosted: Fri Sep 07, 2012 2:48 am    Post subject: Reply with quote

Decided to buy a can of quick start. Let vechilce sit for 24 hrs and sprayed quick start down throat of TBI. The truck turned over about one turn and fired up. Halleluiah, progress. Cool Should have done this sooner. Pinched off vacuum line going to vapour recovery canister. Turned truck over and engine started within one turn. Will have to wait over night and and try again. This is definitely a fuel problem. Looks like I have a vacuum leak but why does the IAC show 30 counts when running?
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dfddfd2



Joined: 27 Feb 2008
Posts: 112
Location: Burgaw, NC

PostPosted: Fri Sep 07, 2012 4:56 am    Post subject: Reply with quote

Please keep us posted. My son is having the same problem with his Blazer.
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n01tk



Joined: 23 Apr 2011
Posts: 39
Location: Nova Scotia Canada

PostPosted: Thu Sep 13, 2012 10:44 am    Post subject: Still looking Reply with quote

I am now looking for any vacuum leaks which may be leaning out the fuel mixture causing a slow start. I am presently constructing a smoke generator to help identify leaky areas. Let you know how well it works.
http://www.fiero.nl/forum/Forum1/HTML/081547.html The Blazer may be a different problem, I would check fuel pressure, there is a mulitude of tests you can do with the gauge installed, good luck.
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n01tk



Joined: 23 Apr 2011
Posts: 39
Location: Nova Scotia Canada

PostPosted: Sat Sep 15, 2012 10:33 am    Post subject: Reply with quote

Built the smoke generator, could not find any vacuum leaks. Smoke white in color and hard to see. Measured cranking vacuum. 2" hg. This is low. Everything I read says 3 t0 5" when cranking. Drawing in air some where? Running vacuum is 15" hg momemtarly than it slowly moves up to 20 "hg ( 15 secs). At idle moves between 20 to 21 and back to 20 in 1 sec intervals. Any ideas? Rolling Eyes
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n01tk



Joined: 23 Apr 2011
Posts: 39
Location: Nova Scotia Canada

PostPosted: Tue Sep 18, 2012 1:50 pm    Post subject: Reply with quote

I did take some propane and went all the way around the base of the TBI, no change in engine speed. Discovered something interesting, when I electrically disconnect the IAC the engine starts 1/4 turn everytime? Appears to start properly. Is the IAC open when disconnected or closed. I need more informatrion on IAC control logic. Another idea is with the IAC disconnected I no longer have the leaning out effect of an additional vacuum leak? Thanks for any help. Question
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n01tk



Joined: 23 Apr 2011
Posts: 39
Location: Nova Scotia Canada

PostPosted: Thu Sep 20, 2012 1:49 pm    Post subject: Reply with quote

I tested the IAC input with a noid light. The noid light flashes with engine running. Lights turning red and green if throttle is varied. Noid light does not flash when key is turned to on position. Also no flashes when key is turned to off position. Noid lights stay lite but don't flash either in "on" position or " off " position. Looks to me the ECM is not running the software routine to park the IAC for cranking? Comments please.
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fstfwd



Joined: 07 Dec 2012
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PostPosted: Fri Dec 07, 2012 9:59 am    Post subject: Reply with quote

I am also experiencing this issue. 91 chevy p/u 1500, 350 tbi, running DynamicEfi EBLFLASH. I have advanced both base and initial timing to match in tunerpro up to 6*, tried varies IAC count changes.

Will be following this post for any suggestions.

thanks,

BW
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billgraves



Joined: 20 Oct 2006
Posts: 17
Location: Memphis, TN

PostPosted: Mon Feb 04, 2013 10:43 am    Post subject: Long Crank to Run time Reply with quote

Hello N01tk,

I did see (might have missed it) the engine in ur 1995 3500. If it's a 7.4L I believe the Fuel Pressure was higher that year for Hot Fuel Handling. (Vapor Lock). If i'ts a 5.7L don't get hung on the IAC.

Let me get this straight. After 24 hrs you crank and it take a "Long" time to run. How long? IF you spray it with starting fluid, there is no long crank to run time. I would first check the basics. Externally run your fuel pump for a min and then turn the key on. Set up for the next day test by plugging OFF the Canister line at the TBI Base. Crank to run. Go this route and you will find it.
Insure a hot engine when setting up for the next day on shut down.

The IAC system "PArks" at a calibrated point. Usually 140 steps. (These steps have no feed back.) Remove IAC and clean it and remove the pintle. I use Anti-sieze on the threads and walk to pintle back down. Lubing the motor as well with a little anit-sieze before stuffing in the lintle.) The cal CAN be changed but Truck adn Bus was very SLOW with IAC movement back then and GM was conservitive because of stalling in some engine families. So IAC walks home slow as Idle comes slow.

The Cal could have a timer or a COUNT to delay fuel just like the Camaro/Corvette has in 86-89. It delays the fuel 8 to 12 revs before fuel so the enigne is spinning. I change this to 1 and the crank to runs are shortened. It can help
There are numerous other items you need to insure.
The correct injectors. Provide us with is the O2 NEW and what brand. (It DOES MAKE A DIFF on the brand).
Grounds soldered and moved away from teh t-stat housing
Block Learns at 30 moh and 55 moh and in DRIVE at IDLE.
What is the iadle spd and IAC counts in DRIVE
IAC counts in Park, hot at idle

I hope this will help
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n01tk



Joined: 23 Apr 2011
Posts: 39
Location: Nova Scotia Canada

PostPosted: Tue Feb 26, 2013 11:37 am    Post subject: 95 Chevy Reply with quote

Hey Bill thanks for the detailed reply. I have replaced the ECU and the truck is starting much more consistant but still has a long crank time when cold. I am going to get the info you requested. Will get back to you, thanks again.
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billgraves



Joined: 20 Oct 2006
Posts: 17
Location: Memphis, TN

PostPosted: Tue Feb 26, 2013 4:22 pm    Post subject: Reply with quote

Hello Nova Scotia,

The small diameter distrubutor has problems as well. My won truck (1977 with a 454 / 4L80-E transplant) has a NEW GM Module, pick-up coil and silicone grease on the bottom of the moduel. I rean a ground strap to a stud I put in the dist base (extra I added) to providea level ground plane.)

Check the magnet on the shaft. If oil got to it it will be very weak VERY WEAK and not enough to induce a large enough voltage into the pick-up coil unless the engine spins fast enough in SOME cases I've seen. Seen Ign Coil female connector ends to LARGE and had a loose female terminal. GOtta replace the couil for this.

Aslo check the location of the Coil to the Distrubutor and the routing of the Moduel to Coil Wire (white and pink) Insure the wire is away frm any Secondary wiring and droops low asap from the coil. I've seen some short ones cause a false trigger to the pick up coil and have other troubles.
This is some of what I look for.

The Grounds are VERY important I will say it again. Soldered and clean. I use STAR washers to ground the grounds. (My Truck has a GROUND BUSS I made with a copper base and brass studs. I use 2 #6 multi stranded groundwires to the NEg Bat terminal to each ground buss. The copper and brass studs are soldered to promote current flow and it looks a bit better. I use a #0 welding cable to ground the alt too. Somewhat over kill but I don't want to walk home ever.)

I have seen a tight ground to an intake manifold measure 0.3 volts on a voltage drop. Using the neg battery for the ground plane. The 0.3 volts was the O2 Ground on a single wire O2. The car was in Buy-Back and acted just like a pluggged cat converter. The ground bolt WAS Tight. It measured 1 ohm resistance. When I volt dropped it the volts went to 0.4 to 0.5 as the throttle and load increased. The scan tool O2 read low as well. I installed a star washer to correct it as a temp fix and it ran great. (The dealers, yea dealers, had ecmed, injectored and cat convertered and complete exhaust the car with spark plugs, Ign coil, pick up ect and al the sensors along with 8 or 9 O2's. To correct this long term, for the owner, I spliced into the ground wire and ran a seperate wire to the Bat Neg wire from teh neg cable and ties them as one.

I hope this will help.

One more. Big or small blocks. You set the Ign timing and the truck runs poor. I';ve seen the damper ring on the balancer SLIP so bad it retards the timing 20 degrees or the ring is so far off I used the Ign Coil wire to trigger the timing lite to find it. I check TDC for al the balancer I suspect.
Hope this may help someone. someday
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billgraves



Joined: 20 Oct 2006
Posts: 17
Location: Memphis, TN

PostPosted: Tue Feb 26, 2013 4:24 pm    Post subject: Reply with quote

Another Item to watch. Reman ECM's. I only use Delco. Had others trick me and ou find another ECM problem. Do it once and not twice.
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n01tk



Joined: 23 Apr 2011
Posts: 39
Location: Nova Scotia Canada

PostPosted: Fri Apr 12, 2013 4:41 am    Post subject: Reply with quote

Hey Bill,

You sound very well groomed around these trucks. I do beleive grounding is a big issue. I have yet to get the truck back out on the road for a good run so the learn function can kick in. Until I do this I am not in a good position to determine the problem. I am doing some body work ( dump box) but will get ahold of you when I get back to troubleshooting the long start time. Thanks again for the reply.
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billgraves



Joined: 20 Oct 2006
Posts: 17
Location: Memphis, TN

PostPosted: Fri Apr 12, 2013 9:08 am    Post subject: When in Closed Loop Reply with quote

Hello n01tk,
I won't waste funds on any O2 other than a Delco. I learned from my job the lessons of aftermarket O2's and saw this at home. I use a Denso O2 but recalibrate the tables. In the late 90's or early 2000's the big block released a bulliten for failing O2's.The Delco was replaced with a Denso and a calibration was nec as well. The Denso O2's function 150 deg C higher, without failure than the Delco's. Delco could have done this but funds were to high for change.
The Big Block really does not need a heated O2. Insure agood grounds and a Good O2. The O2 is like a ni-cad battery and wears out or the end measurements are not aboe to be performed correctly,. I replace them at 40- 50k. Use Chevron Techron fuel additive a few times a year. Helps keep slime build up off the sending unit and injectors clean and a bit of carbon.
Lube or regrease the Ign Module at 50k and clean the pick up coil connector. Keep wires clean and cyl 4/8 and 5/7 apart in the seperators.
It helps more than you know. In 1957 Olds found this. Look at an Olds motor wire seperators on the drivers bank. 5 and 7 are aparts.
Good Luck.
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1227730 IROC



Joined: 22 Mar 2013
Posts: 16
Location: THE LAND OF BROKEN DOWN CARS

PostPosted: Wed Aug 21, 2013 9:07 am    Post subject: Reply with quote

n01tk wrote:
I did take some propane and went all the way around the base of the TBI, no change in engine speed. Discovered something interesting, when I electrically disconnect the IAC the engine starts 1/4 turn everytime? Appears to start properly. Is the IAC open when disconnected or closed. I need more informatrion on IAC control logic. Another idea is with the IAC disconnected I no longer have the leaning out effect of an additional vacuum leak? Thanks for any help. Question


I DID THE SAME THING WITH KEY ON ENG OFF. IAC COUNTS ON TUNERPRO DISPLAY ARE 160 ( FULL OPEN)

ENG IDLES AROUND 1400-1500 AT STARTUP WITH CONNECTOR PULLED FROM IAC ON MY L98 5.7 . THIS TESTS IF THE IAC IS RESPONDING TO OPEN COMMAND. MY ENG STILL DIES IMMEDIATELY AT STARTUP AND IDLES IF I OPEN THE THROTTLE A SMALL AMOUNT. I SUSPECT THE IAC IS GHOSTING OR THE ECM IS NOT SENDING OPEN COMMAND FOR SOME OTHER REASON...
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