Rough idle, misses under load

S

STAGEUP

Member
Hi guys! Well, first problem with the Syclone has turned up at 110,000 miles. The truck had a bad miss under load, and idles rough. It doesnt stall, and it doesnt have any check engine lights either. No codes. So I did the following..

installed a new set of GM plug wires

Installed NGK UR6 plugs gapped at .030, and also check the plugs for hairline cracks

installed a new cap and rotor

New fuel filter

Checked the TPS, MAP for proper voltages

Checked the OHM readings on all 6 injectors, and they read fine at 0.016

Did a compression test and it was perfect.

Checked for any pinched vacuum hoses, or cracked hoses, everything was fine

Im puzzled now, what can be going on?? Could it be the fuel pump? I installed a walbro 255 about 10,000 miles ago. How could it go 10,000 miles, and suddenly give up now? Any ideas? Thanks!
 
skipztt

skipztt

boost
Re: Rough idle, misses under load

well def check the pump. there has kinda been an issue of walboro's being cheap chinese junk pumps and taking a crap on people. i think i even need to check mine out too. :tdown:

but everyone is gonna tell u to get datamaster on ur truck. once you get that on there, you can narrown down your problems much better. especially with these trucks
 
syclone3

syclone3

Member
Re: Rough idle, misses under load

If you can hook up a fuelpressure gauge to some injection hose and an adapter to the stock rail. Just route it up with the gauge under the wiperblade. Take a drive and see what the fuel pressure actually is. We test a lot of cars on the dyno like that. See a lot of fuelpumps that are almost dead under boost on various turbo cars.
 
S

STAGEUP

Member
Re: Rough idle, misses under load

I hooked up a fuel pressure gauge today.

It holds pressure at 45psi with the igniton on.

When the engine is idling, the psi varies from 35-40psi with the vacuum hose connected.

With the vacuum hose disconnected, the fuel pressure goes up to 40-45.

When I rev the motor, the fuel pressure doesnt go past 50psi.

So now, Im pointing at the injectors. I OHMd the injectors, and they all read .016, which means they work, but I havent I havent done a pressure test on them yet. How do I go about powering each individual injector so I can measure pressure drop?

Also, the fuel pressure regulator is the original 18 year old unit. Could the FPR be something to look at?

Another thing, since this problem started, the transmission takes longer to shift, and shifts a lot firmer.

Thanks for any info.
 
BoostedSUV

BoostedSUV

Active member
Re: Rough idle, misses under load

check the timing? mine had a lot of the same issues and my timing was off, the distributor hold down came loose.
 
TYHOGG

TYHOGG

Active member
Re: Rough idle, misses under load

I know it sounds stupid but double check the wires on the cap. its not hard to cross them up.
 
S

STAGEUP

Member
Re: Rough idle, misses under load

Okay guys. Thank you for your input. Ill double check the firing order and wires. And I will check the timing again. Thanks!
 
sytydvr

sytydvr

New member
Re: Rough idle, misses under load

check all the check valves on the vaccum lines there is a particular 3way that gives vaccum to the a.c controls, is located on the passenger side near the egr valve and fpr. the one on mine was shot!!!
good luck
 
S

STAGEUP

Member
Re: Rough idle, misses under load

Okay, well I checked the wires, and timing. Everything was good.

Gonna check the check valve today. This is so frustrating!!! :(
 
S

STAGEUP

Member
Re: Rough idle, misses under load

Changed all three check valves.

replaced all vacuum lines.

replaced throttle body gasket

No luck.

Im just going to pull the injectors now, and have them serviced at AZ TPI.
 
nello

nello

Active member
Re: Rough idle, misses under load

STAGEUP said:
Changed all three check valves.

replaced all vacuum lines.

replaced throttle body gasket

No luck.

Im just going to pull the injectors now, and have them serviced at AZ TPI.
Click to expand...


Injectors would be my next suggestion. I battled a crappy idle for a bit after I bought my truck. I found I had one bad ignition wire, junked vac lines, a cracked injector, and leaky lower intake manifold. Once all that was fixed I added a tune up and my crappy idle was now perfect. G/L. And if you find a bad injector I've got a spare for ya.
 
S

STAGEUP

Member
Re: Rough idle, misses under load

UPDATE:

I did a pressure test on each injector. I gave each one power for 3 seconds. 2, 3, 4, 5, and 6 injectors made the pressure drop from 45psi down to 9psi after the 3 second injector power up. Number 1 injector on the other hand only fell down to 15psi.

So needless to say, I think I found the problem. This will also explain why cylinder 1 was running a lot cooler than all the other cylinders when I did the water spray test on the manifolds. :tup:
 
S

STAGEUP

Member
Re: Rough idle, misses under load

nello said:
Injectors would be my next suggestion. I battled a crappy idle for a bit after I bought my truck. I found I had one bad ignition wire, junked vac lines, a cracked injector, and leaky lower intake manifold. Once all that was fixed I added a tune up and my crappy idle was now perfect. G/L. And if you find a bad injector I've got a spare for ya.
Click to expand...

How much you willing to let that injector go for? Looks like I got a bad one.
 
B

bucwildbob

proud owner # 1662
Re: Rough idle, misses under load

is your coolant temp sensor ok? a bad coolant temp sensor (for the computer, not the temp sending unit for the guage) can make your vehical run really rich, idle badly and cause missing. This will also happen if you take out the thermostat and it never warms up... does your exhaust smell rich? You might pull the plugs and see what they all look like. narrow it down to a single cylinder or a global problem.
 
S

STAGEUP

Member
Re: Rough idle, misses under load

Well, I wanna give a BIG thanks to Nello for shipping me an injector for free! I really appreciate it!

And now, the moment we have all been waiting for!


ITS FIXED!!!!!!!!!! The number 1 injector took a crap! I can't explain how well the Sy runs now! Its amazing! Before the injector went bad, since I bought the truck, it had a slight unexplainable ping, and didn't feel too responsive. Took it to the track one night, and ran a best of 13.8 bone stock. I felt it could do better, but I was satisfied. Then my injector took a crap, and I ended up changing a whole lot of stuff! Now that the injector is fixed, it feels soooo strong!! I can't believe it!! I can't wait to take it back to the strip! :tup:
 
alwayscode390

alwayscode390

pppssssshhhhhtttttttttttt
Re: Rough idle, misses under load

My truck idles with a "skip" in the idle heartbeat too ... but otherwords runs great.

It could use a tune-up though.

Glad you found your problem :) ---
 
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