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Discussion Starter #1 (Edited)
A couple of weeks ago I started a thread to find out what is the significance of injection pump closure time. Several Forum members contributed to my education on this subject. Thanks to: Diesel-T, dieselmike1, THEFERMANATOR, turbovanman & DieselPro.

For reference, I have a 1994 OBDI so I use GMTDScan Tech. GMTDScan uses the term “injection pulse width”. Both GMTDScan Basic and Tech will read “injection pulse width”. I do not know what the other scan tools use to describe DS4 injection pump closure time.

My Conclusions: Good idea to periodically check IP closure time.

(1) Normal closure time: between 1.5 ms & 1.9 ms
(2) < 1.5 can trigger DTC 35 (OBDI) P1216 (OBDII) & >1.9 can trigger DTC 36 (OBDI) P1217 (OBDII)
(3) Closure time moving out of normal spec or DTC’s can indicate a bad PMD. PMD is the first thing to replace, then re-check closure time
(4) If a known working PMD does not correct closure time, then the IP is failing.

This is a summary from the original thread:

Definition of Closure Time: "The DS4 uses a PWM solenoid to control rack travel internally to limit fueling. They measure solenoid closure time as a way of verifying that the solenoid is closing and properly controlling the rack travel." [quote from original thread]

Normal closure time: between 1.5 ms & 1.9 ms. This is also stated in the Stanadyne Service Bulletin SB500R2:1.5ms to 1.9ms
What happens when closure time is outside normal operating parameters:

(a) Stanadyne Service Bulletin SB500R2:
<1.5ms might trigger DTC 35
>1.9ms might trigger DTC 36

(b) "Closure time code 35 sets when the fuel injection solenoid closes at less than 1.2 ms. Closure time code 36 sets when the fuel injection solenoid closes at more than 2.5 ms. From what I have seen trucks with a closure time slightly higher than 2.5 ms run quite well and should not be considered bad in my opinion. Some of these "specs" have been altered in some trucks due to a reflash or model change so your truck could throw a code and still be within usable shape." [quote from original thread]

What does it mean if the closure time changes at different speeds/RPM:

"It shouldn’t change much. If it does that is an indicator of a possible issue" [quote from original thread]

What causes closure time to vary from normal operating parameters:

"The PMD is a major contributor to it since it powers the fuel solenoid. GM even had a bulletin out back in the day to replace the PMD before the pump when a code 35 or 36 popped. I know mine varied some from idle to WOT, but varied from about 1.5 to 1.8. When I had a bad PMD (would stall at idle) the closure time would drop down to 1.2 to .8 when it would stall out. Replaced the PMD and it went back to 1.5 to 1.6 at idle." [quote from original thread]

According to the Stanadyne SB 500R2: causes are:
• Damaged PMD calibration resistor
• Defective PMD
• Defective Encoder Sensor
• Improper IP Poppet Valve Stroke Setting
• Incorrect IP Poppet Valve Spring Preload
• Improper Poppet Valve Stroke Setting (<1.5)

In addition, "Dry " ULSD fuel is bad for DS4 IP's. Everyone should be adding lubricant (2 cycle motor oil, Diesel Kleen, Howes Diesel Treatment, etc) at each fuel stop.

Here is the link to the thread: http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/651794-ip-closure-time-aka-injection-pulse-width-gmtdscan.html
 

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Hell i ain't checking anything as long as they run good.
I have 16 diesels on my farm to maintain + all the other work that needs done
I got no time for that BS,.. i got to sleep too!..jeez! :coffee:
 

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Great follow up. Funny thing is, the customer who's truck died has exactly the same readings on the new/used pump.
 

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What causes closure time to vary from normal operating parameters:

"The PMD is a major contributor to it since it powers the fuel solenoid. GM even had a bulletin out back in the day to replace the PMD before the pump when a code 35 or 36 popped. I know mine varied some from idle to WOT, but varied from about 1.5 to 1.8. When I had a bad PMD (would stall at idle) the closure time would drop down to 1.2 to .8 when it would stall out. Replaced the PMD and it went back to 1.5 to 1.6 at idle." [quote from original thread]

According to the Stanadyne SB 500R2: causes are:
• Damaged PMD calibration resistor
• Defective PMD
• Defective Encoder Sensor
• Improper IP Poppet Valve Stroke Setting
• Incorrect IP Poppet Valve Spring Preload
• Improper Poppet Valve Stroke Setting (<1.5)
"Dry " ulsd fuel should be mentioned as a cause?
 

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"What causes c-times to vary from normal values?"

Electrical malfunctions aside.. IMHO its FUEL SUPPLY SYSTEM DIFICIENCIES for the most part. Many GM and Stanadyne Service Bulletins regarding the PMD failures were IMO carefully crafted fabricated lies to cover up the fact that most factory authorized service centers diesel techs were NEVER properly trained nor prepared for the revolutionary DS model pump. And the adverse effects of the new Tier1 diesel fuel being phased in just as the EFI 6.5TD rolled out didnt help matters but I digress..


short c-time typically indicates air. The lack of the fuels natural resistance causes the popet valve to seat to soon- SHORT time.

long c-time typically idicates contamination, increasing the fuel natural resistance causing the popet valve to seat late- LONG time

For a longer explaination, see explain how the ds4 pump works please.
 
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