Engine/Transmission (1994 - 1998) Missfire

[MHoak]

I got this truck 1 year ago. It is still the same after 15k and several mods. If you listen or feel at the exhaust outlet there is a puffing sound and feel. I have relpaced the exhaust, injectors, dv's, checked compression, adjusted valves, set timing @ 16deg. seems to run ok, but I have never heared one like this and it sounds like poop out the pipe. What should I check next?

 

[bmoeller]

May need to have the fuel injection pump bench tested to see if the flow is balanced between all cylinders, or maybe a low fuel pressure problem, or bad overflow valve.

 

[NHays]

I have the same problem with mine. Its like it has a slight miss but not really. Runs ok, but not perfect and really smooth. I have not replaced injectors or anything in fuel system. But I did have engine totally rebuilt and problem still there. sometimes it goes away and comes back, right after a HARD pull in the hills.

 

[stacerbob]

What year is yours? My '95 was a 160 HP auto once, it has the 1000 rpm chatter real bad!

 

[NHays]

Have you put in a Governer Spring Kit.

 

[MHoak]

I did check fuel pressure and it was ok at the time. It does have a 3gsk, problem there before and after. The sound is noticable at idle and while driveing thru tunnels and next to walls that reflect the sound, so not just idle. I did get a nasty "fishbite" type of miss at 1200-1500rpm after putting in the injectors. drove like that for a week then got a totally dead hole. reinstalled my origonal injectors to fix that. sent them back, they said nothing wrong but sent another set. Reinstalled new injectors. dead hole gone but still had fishbite miss. they said the #3's work fine without pump changes. I put in 191dv's and the fishbite miss is gone but it still sounds poor out the exhaust, seems to idle slightly rough also

 

[MHoak]

I also would like to add that I had a #6 plate in it, but I could not keep the egt's down with my camper on it, going up even 4% grades. Now back to stock plate centered, also have afc spring kit with the stiffest spring installed and starwheel as tight as it will go without coil bind.

 

[Vaughn MacKenzie]

There's been quite a few guys on this board and a few on NW Bombers with a slight miss/misfire issue with their 12-valves. I've come to the conclusion it's a "12-valve thing" and have fought the problem myself for 2-1/2 years & 45,000 miles. My attempts were several different injectors, delivery valves, injection pump swap, new fuel lines, lift pump, valve job twice, all to no avail. Finally gave up and decided to accept my '96 for what it was.



Vaughn

 

[stacerbob]

Yeah from what I've read its typical of some 12V so I just try to not let it get that low RPM after I take off.

 

[MHoak]

the main issue I have with it is the puffing sound and feel at the exhaust tip @ idle, It just says to me that something is wrong. As far as the miss at low rpm under load is concerned, the 191 dv,s fixed that. Of course if I would have left the stock 180 injectors in it the dv's weren' needed

 

[NHays]

I re-adjused my governer springs, and brought my idle up to around 850rpm and that puff all but went away. and the engine runs alot smoother throught the whole power band. Try it, cant hurt nothin.

 

[Vaughn MacKenzie]

MHoak, it could be a problem with an exhaust valve maybe. Have you done a valve adjustment? How many miles on the truck?



Another off chance is a bad head gasket. Sometimes they leak between cylinders. You might also go under your truck while it's idling and look at the vapor coming out the draft tube. If there's a pulse to it that could indicate a head gasket problem. It could also be a broken ring (that's what I think is up with mine). Mine started acting up at 353,000 miles.

 

[NHays]

MHoak, it could be a problem with an exhaust valve maybe. Have you done a valve adjustment? How many miles on the truck?



Another off chance is a bad head gasket. Sometimes they leak between cylinders. You might also go under your truck while it's idling and look at the vapor coming out the draft tube. If there's a pulse to it that could indicate a head gasket problem. It could also be a broken ring (that's what I think is up with mine). Mine started acting up at 353,000 miles.

Not to say anybody is wrong, really, and I don't like Quoting. But, I have just had the whole engine rebuilt, everything is new except the injectors and pump. When I picked the truck up from the shop, I noticed it had almost the same exhaust sound than before it got broken. I did the readjust on the governor springs and brought idle up to 800-850 and the thing runs 100% smoother, and almost NO chuffing. The mechanic(Matt, at Brattain International in Bend, Oregon. just off of Hwy 26 and Empire RD. ) said, "that the noise is from a slight injection imbalance. One cylinder is firing a tad hotter than the rest, it gets more noticable the lower the RPM's are. " now, we might be dealing with a different noise here, which would make this null and void. :{ . I have been told (Oregon Fuel Injection in Eugene, Oregon. and Brattain International) that the only way to fully correct this is to have the pump and injectors calibrated. I have also done a full valve adjustment, because I thought it was a valve after they told me it was not, it did not help at all and I had to mentally "eat some crow" on that one. Just my $. 00000002 on the subject.

 

[MHoak]

In my gut, I am feeling the pump is to blame, since compression was perfect. This may explain why I got a miss with the injectors when DDP said they should not do that. What should I do the pump, Rebuild, tune, calibrate? approx cost?