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odd start

matuva

matuva

Tropical 6.5er
Messages
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Location
New Caledonia. An island in south west pacific, cl
My blazer is acting "funny" sometimes...
  1. was having hiccups while cruising, even though the PMD is new (D-Tech)
    Swapped to a "used but known good stanadyne", and it looks fine for now...

  • Most of the time, let's say 98% of the time, she starts and run fine.
    But, sometimes, she starts and runs like crap.
    I noticed than when she is going to do that, the Glow light just light 1 second and immediately turns off.
    If the glow light cycles normally, I know she wil start and run normal.

    When running crap, MIL comes ON, but no codes show:???:

any idea?
 
I have cleaned the ones on the batteries and the one on the rear of the engine.

I added a groung straight from the battery to the rear of engine...

still had this issue yesterday:
- 1st start, short glow cycle, starts and run rough at high iddle, MIL ON, I switch off;
- wait less a minute, 2nd start, short glow cycle start and run not so bad, MIL ON, no codes with GMTDScantech, switch off;
- wait a little, 3rd start, good long glow cycle, start and ran fine, no MIL ???

PCM?
 
She was quiet last times, doing that randomly but not so often.

But, thoese last days, she does again every morning. This morning, as there's no or very little glow time, she was hard to start.
Then, she started and rev up to aound 3 000 rpms, I shut off immediately.

I succeed then in starting her, she did iddle normal, not even at high iddle cause she was cold, just normal iddle.
Other than that she was doing fine.
MIL ON

After a 15 mns ride. I shut her off.

I key ON, normal glow cycle occurs, started and run fine, MIL Off...

I'm a bit lost.
 
Brooklyn Tow said:
Coolant Temp Sensor.....The one on top of the T stat/Coolant X over, that controls the signal to the PCM for Glow Time?

WAG
Click to expand...

Did you try unplugging the CTS on top of the coolant X-Over......It will increase glow time as well as increasing advance/timing for an easier start.
 
Last edited:
This sounds more like you have a PCM PROM issue.

Thats about how mine acts every time I swap a differnt PROM in. The first cycle is always short glow and hard start, but runs fine immediately. Yours could be from a PCM problem supplying power to the PROM. You said it happened with stock PROM too right? So more likely an external PCM or wiring fault.

If there were a short I would think it would be the PCM signal wire to the Glow Controller to cause the PCM issue of short glow and poor performance.

Do you use any type of battery charger or jump start charger on the truck?
 
No, no battery charger or jump starter with batteries hooked to the truck.

But pevious owner may have done it.

We checked glow plugs and they are fine. I remember that when we changed the starter, I had a glow plug accidentaly disconnected.
She immediately had very short glow cycle.
Once I reconnected the missing glow plug, she immediately did fine..... till next time...

I'm thinking about the PCM. I will try to find out which wire is this signal wire to glow plug and see if it is OK, or even replace it to get sure.

This morning, while the Blazer was acting "funky", I notice that there was a kind of "electric noise" under dash, approximately above the brake pedal.
As soon as this noise appears, glow relay disconnect.
Once she is back to normal, the noise does not show anymore.

It's like a kind of noise that a faulty relay can do. Does that ring a bell to you?
 
With it being intermittent, always hard to determine.

The PCMs wire to the Glow Controller is yellow, exits from the larger pink 32-pin PCM harness, pin/socket C13, which is the row closest to the the clip. It goes into pin B of the glow controller. You can unplug both ends and check for shorts to ground and shorts between wires.

If a glow plug wire is shorted it would likely blow the fusible link, and damage the contacts withing the glow controller. If one is unplugged it loses a parallel resistance so effective resistance goes up and current from the batteries down, so the battery will get pulled down less from less current flow. And the PCM short cycles glows with high battery voltage. Thats why bad glows with high resistance shorten glow times.
 
buddy said:
With it being intermittent, always hard to determine.
Click to expand...
Yes, you're right buddy, and that's what drives me nut :mad2: with the fact I get no codes, even in history,
despite the fact the MIL did come ON.

Thanks for the info on the PCM wire to the Glow Controller, I will check it.

One thing I forgot to mention, though I'm not sure it related to the same problem:

on highway, if cruising at 140/150 kph for a while, there's a hiccup, and the MIL comes ON.
Last time I had the odd start following this hiccup.
Today, it did not show.
The MIL was OFF at the restart...
 
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