Manager Forum

Hey, Im in the middle of trying to diagnose a misfire that became present after the trans was replaced due to a blocked check valve in the cooler.

Prior to this the engine ran smooth with no issues, I know cause its my truck.

The cap,rotor, plugs and wires were replaced because even if they were the problem they were going to be pretty soon. Also made sure there wasnt any slop in the distributor.

That didnt fix the issue so as a guess I changed the Crank Sensor, which is good cause we found a washer stuck to the tip of it. Again it didnt fix it.

ohmed the Cam sensor and its in spec. Checked the Cam sync and its spot on.

Pulled the plugs, none are black or wet.

Did a compression test all cylinders save for 1 and 3 were at 180. 1 came in at 160 and 3 at 140. Test was done warmed up.

Id say that the compression test would verify an issue but I cant see how a smooth running engine with a compression issue would stop being smooth after a matter of 3 days.

The o2 was replaced about 5 months ago and the EGR was done about 7 months ago. I can stall the truck by opening the EGR via the bidirectional controls.

No codes are set.

Im at a loss on this one. I dont see any wiring damaged, loose grounds, nothing. Hopefully you guys may be able to point me in the right direction as Ive addressed most everything that is known to go bad and replaced other stuff that looked marginal with no improvement.

I waqs wondering if you wereable to determine which cylinders are missing? Have you checked the fuel pressure and flow. This all could just be a coincedence that it is happening now. Also have you checked the fuel trims to see what the computer is trying to do? You mentioned changing plugs, wires.cap and rotor. Were htey of good quality. I've been burned before not using OEM for this type of thing. Just some thoughts.

Take a look at crank sensor. I've cracked a few causing a misfire (random). The other thing that pops to mind is the dist cap may have been damaged.

steven kiser wrote:Take a look at crank sensor. I've cracked a few causing a misfire (random). The other thing that pops to mind is the dist cap may have been damaged.

Well, I had similar thoughts but he says he changed the cap and the crank sensor, if I understood the original post.

Yeah Steve, I was going to mention cracked cap, although what i re-rread looks like cap was replaced after tranny. I've seen them up against the fire wall with tranny out. Identifying the cylinder will certainly help

I would check the crank sensor also. Also check the flywheel closely. I know whne I am working on my persoal stuff I may not be as cautious. Ding the flywheel comin out or goin in and ya may have problems. Just a thought.

compression shows all cylinders with in 25% of each other, 25% of 180 is 45. 135 min

I'll assume that no vac hoses got pulled off.

Well, after rereading the post and just not scanning it i see all the replaced parts. I'm wondering if it's a dead skip and not just a real rough idle. The engine may have been forced since the transmission failed. I believe this is the era of the gasket blowing out of the plate on the bottom of the intake. If there is an abnormal amount of vacuum (take off oil cap and place hand over port) that may be the issue. I'm going with (since the initial post was so detailed) there are no codes and the skip can't be nailed down. If the toner ring on the flywheel was bent during the transmission R&R it will cause an issue. Was a ground wire left off? Were the evap hoses crossed?

Guys thanks for the input so far.

I havent been able to identify the cylinder, which would make diagnosis a whole lot easier. I used a timing light on each wire to see if I had any odd misses and didnt see anything abnormal.

I used a laser temp probe on the exhaust manifolds to look for a dead cylinder as well and they all seemed to come up to temp although the outter ones were a bit slower (makes sense since I have two exhaust ports right next to each other in the middle cylinders).

Vac has been verified intact.

I used Napa Echlin ignition parts, not the Mileageplus stuff.

The truck definitely feels like a hole down, it idles stable but it shakes and it doesnt clear up or get worse with RPM.

I had a buddies transhop do the R&R. Im not gonna post their name but they are well known for hi performance Diesel trannies and race trannies in the Rancho Cordova area. At this point Ill assume that the flywheel is undamaged.

I doesnt seem fuel related like a pump going south. I know that feeling where its way down on power and it lean pops. No popping like Im running out of gas.

Ive thought Ive addressed ever potential bad spot in the truck short of a new distributor but Ive had Dodges in here with CMP issues and they dont run.

Ill run it up and see if I have an intake leak.

Beyond that, Im gonna let it go. Its a beater I got from the tow yard a couple years ago and has ran fine up until this but I may just look around for a mid 2000s Silverado. I hate giving up but I have limited time to chase down the issue and I dont like changing parts (although like I said the cap, rotor and wires had seen better days and the rotor was burning up at the tip).

Woah here. Have we gone from a skip to a vibration?

You should be able to power balance with a scan tool (modis, verus etc). If not, try unplugging inj 1 by 1. If the shake doesn't increase with eng rpm then maybe Steve's on to something. Good luck

steven kiser wrote:Woah here. Have we gone from a skip to a vibration?

Well, at some point as I read the posts late yesterday, I was getting the same feeling. Possibly more of a vibration than a miss.