CRANKS FINE BUT WON'T RESTART AFTER SITTING 60 MINUTES OR OVERNIGHT

Tiny
MTRDUDES
  • MEMBER
  • 2001 ALL OTHER MAKES ALL OTHER MODELS
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 336,789 MILES
09/00 Workhorse P42
VIN #5B4KP42R813327341
Chevy 5.7L / 336,789 miles

I have a customer in Savannah, GA with a Workhorse stepvan fleet; I live in Charleston, SC and go there every couple weeks to maintain it. They have a stepvan (info above) that is kicking my butt and would really appreciate your insight. The original complaint two weeks ago was that it was turned off at a route location then would crank over good but wouldn't re-start after 30 minutes or so. It was towed to a local garage and they replaced the fuel pump; it was picked up the next day and driven back but then wouldn't re-start at Unifirst so I was asked to come check it.

I first scanned for diagnostic codes even though the check engine light wasn't displayed and there weren't any; I then checked for ignition spark at the plugs and had good fire. I installed a fuel pressure gauge and checked the pressure key-on at 32 psi at the engine when the service manual says it should be 55-60 psi; when I turned the key off the pressure dropped approximately 6 psi in 10 minutes. I then cranked the engine over and sprayed carb cleaner in the air intake, the engine started and ran and the pressure was 44-48 psi with the needle fluctuating. I inspected the replaced fuel pump and saw nothing unusual but replaced it with a OEM pump and the pressure was 54 key-on and the engine started and ran normally; I also replaced the fuel filter and it definitely had blow-through restriction, the original garage didn't replace it. I road tested the truck and it had very poor acceleration so I removed all the spark plugs since I had never replaced them and found all of the center electrodes worn out and #5 plug fuel-fouled. I performed a cylinder compression test and all cylinders were within 10 psi of 125 psi so I installed new plugs/wires/distributor cap and rotor; I also replaced the oil pressure switch because it was seeping oil. I then road-tested it and the performance was much better, basically what it should be.

By this time it was late and I had to get back to Charleston so I told the location the truck was good. They called me three days later and said the truck ran fine for two days but that morning had done the same thing on the route, cranking but not starting after 30-60 minutes at a customer location. I had originally ordered the fuel pressure regulator located under the intake manifold because the fuel pressure gauge needle was still rapidly fluctuating even with the new pump installed and I thought the regulator may be causing that. I went there this past Saturday with another vehicle tech friend and we rechecked everything I had previously done then checked for the continuing issue. We removed the manifold and replaced the regulator with a dealer/OEM one and checked everything with the manifold off, all looked good. We checked the key-on fuel pressure and it was now at 48 psi but the engine started and the gauge fluctuation was gone. I shut it off and we worked on other trucks for an hour or so then checked the fuel pressure; we had left the gauge connected and the pressure was down to about 42 psi. I attempted to start the engine; the pressure went up to 48 with key-on but had no-start; I found that after 4-5 start attempts and being patient that I could get the engine to start. We disconnected the steel fuel supply line at the engine and fuel filter then used compressed air to blow through the lines; found no restriction but some grayish, dirty fuel came out so I removed the filter and manually blew through it; it had very slight restriction but also the same dirty fuel in it. I then disconnected the line from the filter back to the pump, did the same thing and got the same result; no restriction but grayish fuel. I pulled the pump, inspected inside the tank and saw the fuel was clear all the way to the bottom of the tank with no visual indication of trash or other foreign substance. After reading some more I saw an indication that the MAF sensor may cause a similar condition so I checked the sensor wiring/OK and swapped the sensor with a known good sensor off the same make/model/year stepvan and then waited about thirty minutes before trying to restart, still got the same result with the same pump pressure readings. Regardless, every time it doesn't start I can prime with carb spray and the engine starts immediately and runs good.

I apologize for the long explanation but wanted you to know all the details. I'm assuming the problem is something obvious that I'm missing; that's why I took another experienced tech with me Saturday. I'm going down there again this Saturday and hope you'll be able to give me some positive leads to follow, thanks.
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Tuesday, September 22nd, 2015 AT 11:05 AM

8 Replies

Tiny
DR. HAGERTY
  • MEMBER
Your excellent work seems to have one thing overlooked, are all the injectors OK?
I was having my butt kicked by a GM car and it turned out to be an injector.
At almost 337k miles, just my eye on it mate.
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Tuesday, September 22nd, 2015 AT 11:40 AM
Tiny
MTRDUDES
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I haven't specifically checked into the injectors; the main reason is because when it's running the performance and rail fuel pressure is good. My main thought was that unlike all the other stepvans like this that I've replaced fuel pumps in over the years, this vehicle is the only one that is delivering less than 50 psi pressure with a new OEM pump. What is your thought about the injectors; are you thinking that if the injectors are clogged the engine isn't getting a rich enough mixture inside the cylinders and causing the hard start? How did you end up deciding it was injectors on the vehicle you worked on that was giving you a problem?
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Tuesday, September 22nd, 2015 AT 12:29 PM
Tiny
ALEX_BUENA
  • MEMBER
Here is a video of what I think he is talking about for testing injectors http://youtu.be/Lbdjn_uP85A
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Tuesday, September 22nd, 2015 AT 2:04 PM
Tiny
DR. HAGERTY
  • MEMBER
When warm the injector(s) were a dead short electrically, I found it by disconnecting the injector(s)
Also your "spray and it ran" technique is telling me it is not getting fuel during "start" Can you look at injector pulse width during these episodes
Could it be electrical? What is the cold start strategy in there? Or even warm start

Replacement of the major components has been confirmed and would suggest that the issue is elsewhere, but is it? That fuel color would have me at loss, where did that come from?
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Wednesday, September 23rd, 2015 AT 7:57 AM
Tiny
MTRDUDES
  • MEMBER
I watched the video and got some pointers from it that I'll check out. I'm going there this Saturday so will do the checks on the injectors. Cold start (overnight) and hot start) have the same characteristics; will not start until cab spray is injected inside the breather duct and gets to the throttle body. Also meant to mention in the beginning that this is basically the same type of vehicle as a 1999/2000 Chevy P30 step van, the only difference is Chevy quit making them and Workhorse took it over (Workhorse went bankrupt in 2012 and now Unifirst is buying Freightliner chassis with a Utilimaster body).
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Thursday, September 24th, 2015 AT 7:15 AM
Tiny
MTRDUDES
  • MEMBER
Checked the truck again this Saturday; checked the injectors and firing using a noid tester, all were firing properly. Also purchased a new fuel pressure gauge to check my old one and found out the old one was reading 8-10 pounds less than the new one so fuel pressure to the rail is 56-58 now and the OEM spec is 55-62 psi so pressure delivery is right where it should be. I'm completely stopped by this engine issue, never had this problem in 40 years of wrench turning. Any other ideas or suggestions are greatly appreciated.
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Tuesday, September 29th, 2015 AT 6:54 AM
Tiny
DR. HAGERTY
  • MEMBER
When I worked at the dealership level, there was one car that even the engineers were left scratching their heads about.
It turned out to be a tin whisker on the PCM circuit board.
Who da thunk it?
Connector, conductor, component is a strategy useful in eliminating the wiring harness(es)
Grounds and B+ all checked
So, you are getting an injector signal, spark and it cranks, but wont start without a spray of cleaner. Is that right? Did you pull the injectors and observe spray patterns? Is the intake tract clean, no carbon build up. Just thinking out loud man, only a few hairs left!
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Tuesday, September 29th, 2015 AT 8:30 AM
Tiny
ALEX_BUENA
  • MEMBER
Just throwing out some ideas test battery, clogged cat, fuses fuseable link. Maybe the smallest thing causing your struggle also that video I posted there are other videos of issues that maybe you are coming into contact with by that person.
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Wednesday, September 30th, 2015 AT 1:29 PM

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