suburban misfire

[bramwell]

have a 99 suburban 5.7 with a constant misfire on cyl 1 and 8, random on 4 and 5 check electronics steady spark. did a injector balance test, 7-9 psi drop on all injectors except 1 and 5 they dropped 20 -25 psi.
tried the motovac injector cleaning but no change. the misfire will change periodically even when just sitting and idling. under load and acceleration it sems to smooth out but my guess is the misfires are masked by the other cylinders. the scan tool shows the miss fires on 1 and 8 with intermitten on 4 and 5. I think replacing the injectors is in order. appreciate any comments

[Loekee75]

Originally Posted by bramwell

have a 99 suburban 5.7 with a constant misfire on cyl 1 and 8, random on 4 and 5 check electronics steady spark. did a injector balance test, 7-9 psi drop on all injectors except 1 and 5 they dropped 20 -25 psi.
tried the motovac injector cleaning but no change. the misfire will change periodically even when just sitting and idling. under load and acceleration it sems to smooth out but my guess is the misfires are masked by the other cylinders. the scan tool shows the miss fires on 1 and 8 with intermitten on 4 and 5. I think replacing the injectors is in order. appreciate any comments

what about your plugs/ wires?

[bramwell]

Originally Posted by Loekee75

what about your plugs/ wires?

checked plugs, moved no 1 into no 3 cylinder etc, no 1 still a constant misfire. thinking I may have multiple separate problems here

[zirb]

My 99 did the same thing. Then one day it wouldn't start. It was the coil wire. Just an idea.

[bramwell]

Originally Posted by zirb

My 99 did the same thing. Then one day it wouldn't start. It was the coil wire. Just an idea.

thanks will check it out

[Lu-san]

I have a similar problem on my 96 Sub 5.7 L eng. I get random missfire codes (P300 I think). I have an AutoXray 600 code reader so I can check the missfires on each cylinder. Most misfires on cyl 4, 5, & 6 with vry few on the others. I've changed plugs, plug wires, dist cap, rotor, cam sensor, & coil. Still get the missfires. I haven't had much time to work on it lately (still drivable but the check enginle light is always on). One thing I have NOT checked out yet is that I get a stored code of (P1100). Something about a manufacturer specific transmission code. I'm thinking it may have something to do with the TCC solenoid but when I get a-round-tuit I'll check it out.

You may want to have somebody with a realy, really good code reader (like a dealer or transmission shop) read the codes for you.

[Jeremy-WI]

Lu-san
There is no GM code P1100, it is a problem with the Auto Xray software. I had a phantom P0700 and P1100 when I hooked my first auto xray to my 96 K1500, checked my factory service manual and no mention of a 700 or an 1100 code. Transmission codes are going to be P07?? or P17?? because of the OBD standard. The updated auto xray software should fix the code

[tgperk]

Originally Posted by bramwell

have a 99 suburban 5.7 with a constant misfire on cyl 1 and 8, random on 4 and 5 check electronics steady spark. did a injector balance test, 7-9 psi drop on all injectors except 1 and 5 they dropped 20 -25 psi.
tried the motovac injector cleaning but no change. the misfire will change periodically even when just sitting and idling. under load and acceleration it sems to smooth out but my guess is the misfires are masked by the other cylinders. the scan tool shows the miss fires on 1 and 8 with intermitten on 4 and 5. I think replacing the injectors is in order. appreciate any comments

I have a 99 suburban with a very similar problem. Did you find a solution ?

[WikedKlown]

Same Here... Any Solutions?

[16th hippy]

this thread was started over 2 years ago. would be a good idea to start your own threads and link to this one if needed. mods will likely close this thread down soon and no further posting will be allowed to it. if you are still having this problem, start new thread, include year make and model, engine size and any info on parts changed and so on.