Fuel injector knock

TheBac

Why do I keep doing this?
Staff member
Apr 19, 2008
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So, how about we get back to giving advice to the O/P? I would think doing some more in-depth testing first is in order here, correct?

1) Return rate test, both injectors and CP3
2) Compression test

What other diagnostic tests should the O/P perform first?

Since it was brought up, there are no MAF/MAP codes stated, but maybe the sensors are weakening, but not quite into triggering codes yet. Would need screen shot engine data for that.

I recommend the O/P get the truck into a Duramax-friendly shop and get it properly diagnosed.

I do not question the integrity of long-time members here, nor the advice they give. There is a limit on what we can do, though, since we arent actually working on the truck ourselves. However....after a while, the same symptoms given multiple times by multiple people always point to the same things.
 

Trgglynn

New member
Jan 5, 2024
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Portland, OR
I think you’re all on to something. Sorry for the late update, I started a new job and have have been working a good amount of hours.

Here’s an update. The truck started running very bad: downshifting, hard shifts, low power to where 55 was a challenge to maintain, stumbling idle, etc.

My brother in law, who is an intermediate diesel mechanic, and I listened in and identified injector 8 with a bad knock up by the solenoid, and 4 had intermediate knocking too. Also had some codes pop up for the MAP sensor (can’t remember what they are off of the top of my head). I didn’t have expendable funds so I Affirmed two new Bosch injectors, the sensor, and some gaskets and seals.

I replaced the MAP sensor and the truck seemed to run a bit better. I also ran two bottles of dieselkleen through the tank over two tanks and some performance returned. And after replacing the two injectors the knocking has gone away (so far), and a lot of power is back.

My Bullydog GT (using it as an instant fuel mileage monitor) is still reporting 13MPG.

Now in the past I have gotten P0401 and P0404 codes for my EGR. Kind of a long story, but I have a AFE 4” pipe with a aftermarket cat so it will store those codes and give me a CEL every once in a while which I clear out. Has done this before this issue.

However, now it is throwing a code for a P0102 - Low MAF volume. MAF is reading ~27 g/s.

So what I am thinking is happening is the fuel I was using is shit (pacific pride), and quickly/slowly degraded my fuel injectors over 2.5 years. Only thing I can think of to explain it. Unsure of why the CFR has always been so low though. Also found my FPR pigtail was hagrid, so I replaced that as well.

So it seems like I need to figure out if I have a EGR issue, and if that will affect the CFR. Ultimately I really need EFI live for the diagnostics and tuning out issues..

However the biggest thing which is still the problem is the low mileage..

Sorry for the run on post. I’m going to check my compression here when possible. I checked Cyl 5 that had the +1.250 balance rate and it is 380 with the motor hot. Also did a bottle test and the truck leaks absolutely no fuel during hard pulls. Drove it all jacked up for 15 miles with the bottle plumbed in and there wasn’t a drop.

Any ideas on other diagnosis that can be done? Low MAF readings? Other fuel related issues?
 

Ron Nielson

Active member
Oct 11, 2009
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Berryton, KS
Our trucks normally will have a MAF reading of close to 40 gm/sec with the EGR closed. Your reading sounds like the EGR may be open to some extent. When the EGR opens, the MAF reading drops because that exhaust gas bypasses the MAF sensor. There have been several posts over the years about MAF in the 25-28 range.
 

2004LB7

Well-known member
Dec 15, 2010
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Norcal
Yeah. Either the EGR is stuck open or the filter/intake is clogged. If you are sure the MAF sensor is ok
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
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Phoenix Az
You will set maf codes with a stuck open or partially open egr valve. Make sure the intake horn is tight to the turbo and you didn’t miss clamping it (if it was ever removed). That being loose or not seated will set those codes too.

Now that your LDS injectors are out, send them back to them and see if they will warranty them. Then you will have two injectors to put back in if more go.
 

Trgglynn

New member
Jan 5, 2024
24
4
3
Portland, OR
Our trucks normally will have a MAF reading of close to 40 gm/sec with the EGR closed. Your reading sounds like the EGR may be open to some extent. When the EGR opens, the MAF reading drops because that exhaust gas bypasses the MAF sensor. There have been several posts over the years about MAF in the 25-28 range.
After my mileage dropped, I removed the intake cross over pipe from the top of the EGR. It wasn’t too sooty in there, probably a 1/16” or less of soot. I cleaned the valve with a bore brush on a drill on the valve and seat. Definitely not the best method, but enough to get it to seat I would think. My MAF was reading lower, and after cleaning it seemed to come back up to 40~GM/sec. To be honest the EGR has given me nothing but problems, I have already replaced it once.. do you think taking it off for a full clean with a mild degreaser would help? What are the chances of something goin on with the solenoid? Like it not returning to 0 once the engine is on.
Yeah. Either the EGR is stuck open or the filter/intake is clogged. If you are sure the MAF sensor is ok
I’m fairly sure the MAF is ok. I have a OEM in now, and last I checked it read the same as another Hitachi unit I have. Neither one changes how the truck runs if I swap them out.

You will set maf codes with a stuck open or partially open egr valve. Make sure the intake horn is tight to the turbo and you didn’t miss clamping it (if it was ever removed). That being loose or not seated will set those codes too.

Now that your LDS injectors are out, send them back to them and see if they will warranty them. Then you will have two injectors to put back in if more go.
Thanks for the heads up! When I pulled my injectors I tighten up the horn good with a socket. Should be ok I think. Definitely going to send me old two in for warranty and see what they say. I noticed when I pulled the injectors the bodies had diesel on them between the rubber oring and the nozzle. Only thing that makes sense to me is diesel is seeping out of the nozzle maybe? Maybe it’s irrelevant because at such high pressure there wasn’t a ton of diesel on the bodies.

This stupid Cali truck though.

Here’s one to run by you all. Since I have started having this issue, I have had the baro sensor go out, map sensor go out, and now something is going on with the EGR/MAF readings. I noticed my alternator output occasionally going up a bar or so above 14v on the dash cluster. Is it possible the alternator is over powering the system? It seems like these OEM sensors should last longer than 2.5 years/~30k miles.

Also, if I happened to be getting poor quality fuel over the past 2.5 years which caused the injector failures, would the FPR be suspect for idle inconsistencies? It doesn’t lope. After its warm and sitting at an idle it has a “miss” feeling to it.
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
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IMO if you're sending any to be tested I would send them all, not just a few. LDS will charge you for testing, keep that in mind.

If they are under warranty and they fail, they better now. That would be a crock of shit
 

Bdsankey

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If they are under warranty and they fail, they better now. That would be a crock of shit
They charge for testing up front and I believe refund if there is an issue. I've had a customer that went down that route and LDS claimed they were fine which is where my skepticism comes from. Sent the same set to Exergy and DDP, both stated they failed. After a ton of fighting LDS refunded the customer his entire order and testing fee after the injectors were sent back.

It cost him somewhere around $800 total to have them tested by both facilities.
 

Trgglynn

New member
Jan 5, 2024
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Portland, OR
They charge for testing up front and I believe refund if there is an issue. I've had a customer that went down that route and LDS claimed they were fine which is where my skepticism comes from. Sent the same set to Exergy and DDP, both stated they failed. After a ton of fighting LDS refunded the customer his entire order and testing fee after the injectors were sent back.

It cost him somewhere around $800 total to have them tested by both facilities.
I can’t speak to other’s experience, but in the past I sent in two injectors at different times and they were tested. One of which I bought a new replacement and when the one I sent in failed they refunded me the balance of the new one I bought. I was not charged for testing of either.
 
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Bdsankey

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I can’t speak to other’s experience, but in the past I sent in two injectors at different times and they were tested. One of which I bought a new replacement and when the one I sent in failed they refunded me the balance of the new one I bought. I was not charged for testing of either.
I'm glad your experience was different than my customer's.

This customer's set was a SAC65 for an LB7 that made oil from dribbling nozzles since day 1.
 

Trgglynn

New member
Jan 5, 2024
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Portland, OR
I'm glad your experience was different than my customer's.

This customer's set was a SAC65 for an LB7 that made oil from dribbling nozzles since day 1.
On another note, since you deal with this more than I do. Is it typical these days for new Bosch injectors to last 30k miles? Or is it more likely bad fuel is the culprit?
 

Trgglynn

New member
Jan 5, 2024
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3
Portland, OR
Some basic about the EGR system in the attachment
Thanks for that. My EGR seems to be operating per that data sheet. But, at hot idle when EGR is enabled I have a engine knock off and on. It is subtle, but I can feel the engine shifting from the seat. MAF is 27 gr/s. With the EGR of the MAF is back up to 42 gr/s. I wonder if because the truck is fueling lean if the exhaust gas is causing the miss because it is too lean.
 

Bdsankey

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On another note, since you deal with this more than I do. Is it typical these days for new Bosch injectors to last 30k miles? Or is it more likely bad fuel is the culprit?
No that's not common at all. Current Bosch injectors tend to last much longer than that. With quality fuel, good filtration, and lube added it's not uncommon to see updated Bosch run 75-100k+.