mdm6713

I changed the CPS already...and actually this truck was at a chevy dealer...who couldnt do much...the fiddled with it..but its fine...timing chain is a non starter?

billbobagns

Simple way to see if injectors not opening is causeing no-start.

-remember, sophisticated and measured injector pulses are required for good power, low emissions and good fuel economy, but not for basic "starting". Just get some combustible mixture in the in-take. If compression and ignition are good, it will start.

I like to use a little shot of Berryman's "B-12" Chemtool in the intake. If all poppets or injectors are closed, the motor will start and run a few seconds.

mdm6713

My motor starts and runs...just got a really bad miss.and failed the idle portion of my emissions testing..ive put 90K on this motoro myself.i dont know if its orig. or not with the clock at about 260K now. What would be common sense things to check for? Since ive replaced about everything thus far

bowtieman63

Bronzebogen,


I just joined the site. I have a p305 misfire after changing the usual tune parts for these engines. I noticed on mine that I had raw gas shoot out of #7 when I was base timing the engine after I had pulled the distributor to clean corrosion that GM had put a TSB out on..... I wish I had joined sooner to post the suggestion to you.
Have you tried swapping the o2 sensors to see if the problem moves to the other bank? Also, How many o2 sensors do you have, 4? When the straight pipe was installed did they put fittings in to insert the 02 sensors into the exhaust system? if not you will have NO reading from this side and I suppose you would have a rich setting that will flood the odd number bank. Just a thought

DuaneB

I have the same problem with my 1999 GMC Suburban 4x4, After looking into this for hours upon hours, I found that GM has a recall on the SCPI and were replacing it with the MFI. It continued to throw the P0300 code until I replaced the SCPI and went with the MFI. After the dealer replaced all the known parts (Fuel Pump, EGR, Fuel Pressure Regulator, and suggesting the new Spider assembly, Plugs, Wires, Cap, Rotor, ect It now works great but can not figure out why GM won't pay for the replacement due to their mess up. I know the Suburban is 14 years old and I am the 2nd owner they should atleast do something. Guess thats what I get for thinking

voypro

The spider injector is crap. Replace it. When you get underneath the plenum (plastic upper intake ) you will see a lot of carbon residue, that is normal. One sure sign that you have a bad injector is you will see very clean areas on the aluminum of the lower intake. This is calls by fuel washing away the Black Carbon residue. This means to fuel injector is squirting gasoline instead of turning it into a fine mist.

If and when you replace your fuel spider with a new fuel injector THE BRACKET THAT HOLDS THE FUEL INJECTOR IN PLACE IS SUPPOSED TO BE LOOSE. IF YOU CHANGE OUT THE BRACKET (WITH THE NEW BRACKET WHICH COMES WITH A NEW FUEL INJECTOR IN MANY CASES ) IF YOU ATTEMPT TO TIGHTEN IT DOWN YOU WILL STRIP OUT THE SCREW IN THE ALUMINUM LOWER INTAKE. The bracket is held in place with a torque bolt, tighten it down with the proper amount of torque (I'm not sure what that is) but do not strip it out. AGAIN, the bracket is supposed to be loose.

One other thing if you are experiencing a lot of strange codes and hesitation when you attempt to accelerate look for where your computer is on your vehicle. If your computer is placed underneath your brake fluid and power steering fluid reservoirs. That may be your problem. If your computer is located there, they had a chronic problem of corrosion which literally breaks the bolt heads off the Computer housing and allows moisture to get inside the computer and causes computer to mess up. When I removed my wire harnesses from my computer the bottom two harnesses were extremely hard to remove and one of them was literally fused with the computer. (if you're forced to replace your wiring harness to your computer make sure you are very careful when you cut off your old harness as there are several of the same types of wires, if you simply cut them all off at the same time you will be in very deep trouble. My suggestion is to do a few wires at a time, transferring the wires from the old harness to the new harness and never cut the same colored wires at the same time)

jimiheadstone

hi all, went nuts with the misfires as well. Did full tune up changed fuel filter still a misfire. 1999 gmc suburban 162,000 5.7 vortec
Bought a fuel pressure tester this is a must have.
connected the gauge, turn the key to the on position do not start, 40lbs of pressure. Turn the key a few times to the on position with out starting goes to 50. start truck 50 lbs..... shut it down it drains down to 0 in less that 1 minute. Ok most would say, Fuel injectors and gas module on the spider. Nope most people do not realize the fuel pump can get lazy. It also has a ball check valve in it that can relieve pressure from the lines if problem.
So 1st thing I did was change fuel filter and retest fuel pressure.... same readings.
I remove the tank and also discover gas tank has pin holes and is rotting around the flange..... common problem because water sits on top of tank with dirt. Ok new gas tank. got it for 165....... put old fuel pump in take readings.... better goes to 50 now but needs to be close to 60...... change fuel pump.
fuel pressure now 62 in the on position and while running. Fuel pressure holds steady for 30 minutes........ No misfire codes for 6 months now

Dave549

New twist on this old thread...

My '99 1500 has developed a shudder that I've been chasing for over a year and this thread has gotten as close to matching as anything I've found but with a few twists.

I have an intermittent shudder that feels like a couple of plug wires are crossed. Only shows up when I'm easing back on the throttle. Goes away on accel or decel, doesn't show up at all when I'm running cruise control. I'm getting a little bit of hydro locking as described here, but only for one or two revolutions. The hydro locking is worse when the weather's warm and I've just shut the engine off a for a few minutes. When I fill up, I can smell gas when I get out of the truck which I have been attributing to a bad filler neck seal, but after reading part of this thread I'm not so sure. After the first or second rollover, it fires right up, idles smooth, doesn't seem to skip at any speed.

Gas mileage isn't great (about 15.5 on cruise lightly loaded, drops to around 10 pulling my 6x10 enclosed trailer), but it has a trailer towing package and what appears to be a 3.55 rear axle so I wasn't expect great economy but would like to see it do better than it is.

The truck is a Frankentruck (salvage title) that I bought about 2 yrs ago with 54K showing on the Odo. Now its about 70k. From the carfax I know the truck sat a lot over the years and I've figured out it had a different cab transplanted on it (carfax showed a rollover at 29k miles). I bought it with a major brake problem (as in wouldn't stop) and previous owners had done a lot of part swapping chasing the problem, a process that I repeated unsuccessfully until about 16 mos ago when I figured out the cab must have come from a 2500 or bigger as it had a hydroboost pedal which didn't move the actuator rod in the vacuum booster enough to effectively stop the truck.

After getting that sorted out I started driving the truck regularly and after 2 or 3K miles this shudder started showing up.

From this forum it sounds so far like an injector leak. But here's the catch. I get No check engine lights, no misfire codes, even when it shudders hard enough to make you think a wheels coming off. When the shudder starts, I can mash the gas harder or let off and it stops, ease back in and it returns. Sometimes it doesn't do it for days at a time, some days it does it repeatedly, though most often in the first 5-10 miles or so of driving from a cold start.

Plugged in the scanner, rode down the road and watched the O2 readings. Bank 1 shows both sensors ranging from .015 or so up to about .9. Bank 2 showed readings steady in the mid .7's on both front and back sensors. Pulled the plugs, all looked equally burnt so I replaced them, saw no change in the shudder but the Bank2 O2 sensors started ranging down to the mid .5's up to upper .7's. Fuel economy didn't change.

Some articles similar to this pegged it on the ECM, so I bought another one off Ebay but haven't put it on yet as I found another article that said faulty injectors were usually what fried the ecm, so I don't want to take a chance without a little bit more insight into this. I also don't want to fork over $300 for a new injector setup unless I can get more confident that's what the problem is.

Any light you guys can shed on this subject would be greatly appreciated.

bowtieman63

Have you noticed or can you tell me what speeds and gear your truck is in when it does the shudder? I am wondering if you might have a transmission torque converter clutch shudder. This would happen when the torque converter clutch tries to engage. It will feel like a extra shift depending on how hard you are on the accelerator.................

Dave549

Thanks for looking, Bowtieman63.

The shudder occurs in high gear, usually after lockup, at speeds of 35 up to about 60. Always at light throttle pressure, as in just maintaining speed on flat ground, attempting slight speed increase or encountering slight uphill grade. Seems to be worse on low humidity days, seldom if ever on a damp day. Give it a little more pedal or back off and it goes away. Mostly occurs on cold starts but occasionally shows up after extended run time (I live out in the country so it's a 30 -60 min drive to darn near everything). Never feel it under cruise control. Once I feel it I usually just work the pedal to avoid that loading scenario and then I may or may not feel it again that day.

Once when it hit, out of frustration I decided to just hold it at that throttle setting to "see what breaks" so I'd know what to fix. It did something strange - it cycled on and off at about 4-5 second even intervals. This went on for 5 or 6 cycles before I gave in and stopped teasing it.

As a side note, the hydrolocking has occasionally been serious enough I wondered if it was going to actually start, barely rolling over 5 or 6 times then firing right up. The few times that has happened has been with a hot motor on a hot day and a restart after only being shut off for 3 - 5 min.

Replaced battery, then starter last year but that was towards the end of the hot weather. The mild hydro locking (1-2 rev's) continues unless the truck has sat for several days. From what I've seen on the 'net and the dark carbon ring on the throttle body and the fuel pump always need to prime when I turn the key, I'm guessing that one is a leaking fuel pressure regulator or spider line.

Based on the info in this forum and others, I bit the bullet yesterday and ordered a new MPI conversion unit. Still, I'm not convinced that is the source of the shudder. While it's likely the cause of the hydrolocking and not-so-great fuel economy, I'm not getting CE lights or trouble codes for misfires.

Thought about the tranny as a potential source and about 6 months ago I did a filter/fluid change and put in synthetic with no detectable difference. Truck history (carfax) indicated it sat for long periods of time over the years, and when I got it every seal on it started leaking after about 300 miles of driving (tranny, diff, engine, power steering). After replacing the speed sensor seal and tailshaft seal I put in some tranny sealer to swell the front seal. That was about 3000 miles before the fluid change. The shudder was there before adding the tranny sealer. Got all the leaks (and some other issues) under control, but the shudder won't give up.

Just a thought....is the tranny in this model controlled by the ECU or a separate box? Have a few other gremlins (like lack of a ground signal for the AC compressor that disappeared last spring) that point to a going-bad ECU.

Bought a used ECU off ebay programmed to my VIN a couple weeks back but haven't gotten it to take the security code yet. Only had time for 2 attempts - didn't think to check bat voltage before attempting, checked after 2nd failure and got 12.05 v - min req per the box seller is spec'd at 12.4v so I can't claim it a failure yet. That last attempt was yesterday. Too darn cold to go out there today to tinker.

Any insight is appreciated.