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Discussion Starter #1
My 95 is starting to surge at idle. I don't notice it when it is cold just when its up to temp. I just noticed it today. It surges about 50-80 rpm according to my scanner. I know that isn't much but I just have a feeling that it is a sign of things to come. History of truck
149000 miles
PMD in bumper cant remember brand I think its a D-Tech harness is from badger diesel if I remember correctly.
Injectors replaced about 1-2k ago
Lift pump& OPS replaced 5-600 miles ago.
No tank sock pre filter installed 5-600 miles ago
I don't at this time have a way to test fuel pressure. I know the lp and ops are new and both are ac delco brand but in my experience new doesn't always mean good. I haven't had time to get clear fuel line installed on the return line. Its on my list to do going to try if I can find some locally tomorrow. Anyone have any ideas of where to start?
 

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Check your fuel lines for any kinks, corrosion, weeps, leaks etc.
Clean your FFM and the small screen manager in the bottom of the FFM.
Install a piece of clear fuel line on the return side of the IP to help locate any air in fuel
Fuel pressure gauge would be very helpful
 

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Discussion Starter #3
Pressure gauge is in the works. Had plans to get a couple guages bought stuff happened and money had to go elsewhere. I know when I was under it removing the tank sock and installing the prefilter none of the lines where kinked after everything got put back into there correct places. Im hoping that I can get it on a hoist tomorrow as well so I can get a better look at things.
 

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Are you talking about prolonged surges (greater than half a second or more) or short spikes of increased RPM?

My 99 Suburban did the latter a few years ago, and it gradually got worse until it was not safe to drive in traffic.

Turned out it was a bad crank position sensor.

Cheers,... Jon.

Sent from my Moto G (4) using Tapatalk
 

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Yeah the FFM are prone to leakage among other issues.I threw mine out long ago and retrofitted to a racor spin on 2 micron secondary filter on all my trucks.
 

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Discussion Starter #6
Are you talking about prolonged surges (greater than half a second or more) or short spikes of increased RPM?

My 99 Suburban did the latter a few years ago, and it gradually got worse until it was not safe to drive in traffic.

Turned out it was a bad crank position sensor.

Cheers,... Jon.

Sent from my Moto G (4) using Tapatalk
Best I can describe it is it sounds like a slightly cammed gas engine. Rpms go up and down roughly once every second or so. According to my scanner it drops below commanded rpm then picks up above commanded rpm. It drops 20-40 below and on its way back up its 20-40 above.
 

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Discussion Starter #7
Yeah the FFM are prone to leakage among other issues.I threw mine out long ago and retrofitted to a racor spin on 2 micron secondary filter on all my trucks.
I would like to do something like that. I have the parts to change over to a spin on filter just have to get the time to do it.
 
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That would be the best thing to do when you have some time to spare.I put two fuel filters on the three trucks I have and secondary filtration on my two diesel cars.Its the best thing since sliced bread for sure.Your injection pump and injectors will thank you for it.
 

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"Big Cam Surge" ECM coolant temperature sensor.. Unplug to test. Located on top of motor.
 

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Best I can describe it is it sounds like a slightly cammed gas engine. Rpms go up and down roughly once every second or so. According to my scanner it drops below commanded rpm then picks up above commanded rpm. It drops 20-40 below and on its way back up its 20-40 above.
Ok, that doesn't sound the same as what mine was doing when the CPS went out. Mine was random spikes of up to a thousand RPM, causing it to lurch forward if in drive.

Every time I pulled up at the lights I'd have to leave at least a car length between me and the car in front, and stand hard on the brakes to make sure I didn't rear-end them.

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"Big Cam Surge" ECM coolant temperature sensor.. Unplug to test. Located on top of motor.
That reminds me of another issue that I had that would give uneven engine RPM in various situations.

Whilst driving, under light loads, I was seeing a 'surge' of about a hundred or so RPM, occasionally followed by a 'Coolant temp sensor CCT fault' code being thrown. (I can't remember the number for that one.)

Chased my tail for weeks on that one - the sensor tested fine, replaced it anyway but still no change, disconnected it and spoofed the signal at the ECM and it ran fine, finally found the fault in the form of a poorly crimped wire in the engine harness plug where it meets the body harness.

Moderate bumps in the road were causing the wire to pull out of the back of the pin, I suspect this was causing the ECM to read cold (or hot - I can't remember if the sensor is NTC or PTC) and adjust parameters accordingly, giving what felt like a surge.

Pulled the pin out of the Deutsch connector, crimped it on the wire properly, put it back and the problem went away and hasn't come back. The solution cost me $0.00 but plenty of hours!

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Discussion Starter #12
"Big Cam Surge" ECM coolant temperature sensor.. Unplug to test. Located on top of motor.
I wouldn't say "Big cam surge" Maybe a mid size cam. I will have to get my meter out tomorrow and test since I don't have my scanner at the moment. I do remember it was reading 201 degrees when I did have my scanner on it when it was doing its surging.
 

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Discussion Starter #13
Been busy with work and havent been able to update. Couple days ago after work found a nice puddle of fuel on the ground under the truck. Found one of the lp fittings loose. So far surgeing is gone. Now sometimes I have a issue with on cold startup sounds like a misfire and stumbles almost stalls then clears up and runs fine. Ugh why can't I go a month with out haveing to do something to this thing lol.
 
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