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Uneven firing at 950-1200 rpm

D

dtreid

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Alberta, Canada
98 Chev 2500. Between about 950-1200rpm there is a slight unevenness in engine running. It does this regardless of throttle setting or engine load.
Above and below this rpm the engine runs smooth as silk. There is no smoke at all.

I've got a video uploaded on youtube

http://www.youtube.com/watch?v=vMLBTbzeZ5w


Any ideas?
Wondering if it's a bad injector. These ones have probably 200000kms on them at least.
 
Can you hook up a scan tool or software and see if CTIME is getting above specifications when that lope happens? gmctd taught me that can be caused by a bad ignition switch or bad grounds.
 
I don't have access to a scan tool unfortunately. I've just swapped this motor in, and did a careful job of cleaning the grounds while I was at it. I guess the more important question is, will it damage anything to run it like it is?
 
Sounds like a diesel :)

What kind of fuel has your friend been using? And additives?

Any more details? No codes, and no smoke ever, during start?
 
The trucks running winter diesel right now. The motor that I've put in it sat for at least a year before I got it. I ran it for probably 1/2 hour before doing the swap. I've dumped in an additive called Diesel Injector Cleaner. I'm not getting any codes, and no smoke on startup.
 
was the IP transplanted in place, or did you install it? Was TDCO and timing set since the swap? And the previous truck didnt have the issue and it was turbo truck? What happened to the last engine in this truck?
 
Transplanted engine was from a 94 N/A 1500. I just added the turbo to the 'new' engine. I swapped it without removing or changing pump timing. The last engine in the truck got a cracked block. I have not done a TDCO or timing check since the install. Would this help?
 
So its a 94 L49 "P", mounted into an L65 "F" setup. You are using all of your intake and computer and everything from the 98.

I would do a TDCO and IP timing set. Make sure the TDCO is around -.5 and the IP idle IP timing is at least 3.5* and you have an idle fuel rate of 7-9mm3. I like my idle IP timing higher though, more like 8*, quicker off the line, but engine does not idle as smooth. Mine idles really smooth at about 4.5* idle IP timing.

I dont have my manual with me, Im traveling right now, but I was thinking the timing is different for the L49 vs L65.
 
I used the block, head, and IP from the N/A engine. I swapped over everything else.
Can I do TDCO without a scanner?
 
Youre going to need a scanner, as NVMilton originally recommended. Maybe you have a friend thats a GM mechanic?

Did you put a 94 block in a 98 2500 or move everything from the 98 over to the 94?
 
I'm telling ya.. it's ground or ignition switch related, check the voltage at the PMD. When ya hit that rpm range, I am betting that your ctime is long and just under setting a code.

GMCTD knows all.. and what he doesn't he can fake really well. :D
 
The only ground that I didn't clean is the one on the actual injection pump. Could this cause the problem?
Could it be old dirty injectors?
 
It could be a number of things, but replacing parts is an expensive diagnostic method. Which is why its nice to have access to a scanner from a buddy or friendly mechanic. it would take all of 5 minutes to check everything.

Where is your PMD located? What resistor is in it?

It could always just be a funky IP too. Is there an optical sensor harness filter on there?

What model of IP is it?
 
Yes, the one on the injection pump was the bad one on mine. You can check it with a volt meter at the PMD with pin leads. If the voltage is less than measured at the battery (mine was 1.24 volts lower), your stumble could be caused by grounds or your ignition switch.

I was like 15 minutes from ordering a new injection pump when gmctd told me to check the voltages before I waste a bunch of money.
 
The PMD is still on the pump with a #5 resisitor in it. The pump is a 5521, and I'll have to check if it has a filter harness on it.
 
I swapped filter harnesses and cleaned the ground on the pump. It's maybe a little better, but not completely gone. Not sure what else it could be.
 
Do I need a scanner to check voltages? It also seems to sort of come and go. Doesn't seem to matter if things are hot or cold.
 
Nosir, a voltmeter with a set of pin leads will do the trick fine. I use a $3 one from Harbor Freight that I keep in the truck.
 
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