I'm not sure if anyone has seen any of my posts regarding spider injectors but, I figured I'd try a thread .. I really need your guys' expertise as me and my mechanic are stumped.

- One month ago my truck became increasingly difficult to start. Sent to dealer for diagnostic, revealed bad MAF. They cleaned it and was great for about 2 weeks then became hard to start again. Took to dealer again and had MAF itself replaced .. no change.

- Came back again a third time and after hours of diagnosing and searching, the dealers best electronics guy determined that my spider injector harness needs replacing as its leaking fuel into my oil. Also suggested intake gaskets. They quoted me over $3000 for the whole job so I decided to shop around.

- Aquired a new upgraded spider from AC Delco which improved the CPI to a MPFI. Found a mechanic who works for dealer and also on the side for people like me who can't afford 3 grand. He brings home the GM diagnostic tool for jobs like mine.. it revealed a misfire in cylinders 1 and 2.

- Over the past week and a half we have done the following work, all OEM AC Delco or Delphi parts:
1.) Installed the new spider
2.) replaced upper and lower intake gaskets
3.) replaced MAF sensor
4.) replaced fuel filter
5.) replaced fuel pump
6.) replaced coil/plugs/wires/cap/rotor
7.) ran an injector cleaner through a vacuum line (a little trick dealers do apparently)
8.) oil change
9.) collant system flush
10.) reset the fuel trims and crank via GM diagnostic tool
11.) replaced air filter

After doing all of this, I *STILL* have a rough idle and it has now even stalled out a couple times on me at a dead stop today. The strangest one is the spider itself actually makes a squealing noise during pre start up pressure build up from the fuel pump. Its not the fuel pump hum that we all know about .. this squealing sound comes from the top of the spider itself. It however does not make this noise if the fuel has bled back into the tank from sitting a little bit but, if i stop at the store and come back out to start it, it squeals.

My mechanic then after all of this admitted he has no idea what the issue is and is stumped, and so are his coworkers. The only thing he can think of is the new spider is faulty. Its important to mention that the diagnostic tool says there are now no misfires at all but the truck stumbles like crazy intermittently throughout idle .. however it drives and accelerates fantastic.

I would really appreciate any detailed info from anyone on this site because i would not want to give up and sell it. I'm a student and am running out of funds to figure this out ..if you happen to know what would correct this issue, I'm all ears!

 

I currently have a stumble occasionally at idle also. Mine I believe is fuel pressure. With a fuel pressure guage on check if pressure is dropping to 49 psi or that area when it stumbles. 50 psi seems to be the magic number on mine. If I push the pressure relief valve on the pressure tester while the motor is running it immediately stalls out. With other chevy vortecs 96 and on I have actually used this valve to pump fuel out of tanks while engine is running instead of siphoning it out. Maybe you have a fuel pump volume issue. Check to see how much it pumps out in the specified time. I'm not sure but I think its about a quart in a min. My pump seems to have just enough to keep pressure good for running and even goes up a little when the vacuum changes when giving it the gas. As soon as I touch that pressure relief valve on this one it stumbles. If I fully press it the engine dies. Again others I have tested had enough volume to pump out the tank and still keep the engine running fine. Food for thought. Just because you replaced fuel pump doesn't mean its working. Idle air contol valve may be something to look into as well.

 

Thanks for the reply! My mechanic has gone as far as saying maybe i have a faulty pump and/or spider but really ... what are the odds of buying two defective brand new parts at the same time! .. would be just my luck tho! My fuel pressure checks out.

I think i may try the IAC next as a faulty one depicts the exact same symptoms that I'm still having .. either that or get another spider ... **** me this is getting really expensive and very stressful

 

I understand the money issue. I have so much in my current project I have to continue just to be able to get some of my money back. No one want to pay for repairs that have been done to a car that isn't running correctly. On the fuel pressure. It can have good pressure and still have low volume. It only needs to not maintain pressure for a split second to cause a stumble and then recover if pressure recovers quickly. I'm experiencing this now with my project. 2001 blazer.

 

In all my searching I've never heard of a squealing spider assembly. That's very interesting. All excess pressure should be retuning to the tank without enough restriction to cause a squeal. Could there be a internal leak in the spider or regulator. But it passes leak down tests right?

 

Fuel pressure is tested with the engine off, and the fuel pump running. GM does not publish any "engine running" specs due to far too many variables being involved.

1998 and newer S/T series vehicles have a vacant terminal in the underhood fuse panel. The circuit goes directly to the fuel pump. It is commonly referred to as "pump prime circuit". Applying battery voltage to the terminal activates the fuel pump continuously.



Connect the fuel pressure tester to the service port.
Connect one end of a fused jumper wire to battery positive.
Connect the other end to the pump prime terminal.
After pressure stabilizes, note fuel pressure and write it down.
Disconnect the jumper wire.
Wait 10 minutes.
Note fuel pressure and write it down.
Post the results.

 

Captian Hook:

Is the volume test also done with this terminal and engine off? In the past I've been able to do the volume test with the engine running and using the relief valve and hose. Engine running may have distorted my results. I also believe my above test parameters are off. 30 secs not 60?

 

Yes, you can use the pump prime terminal for the volume test, and also for draining the tank via the pump, (if the pump works). When testing volume, the engine must be off. If the engine is running, the fuel that's being consumed by the engine will skew the results. Spec is one quart in 30 seconds.

 

Thanks for the tips guys! A bit of luck came my way today:

After noticing today that my "mechanic" didn't in fact install the lower intake gasket, nor did he flush the coolant and yet charged me for both, I decided that was enough for me to go elsewhere .. too many bad things happening and surprises with this guy, who knows what else he claimed to do but didn't. I found a great mechanic who came recommended from a number of people I know and within 10 minutes, he ran a test, threw in a new Temp Sensor, and there you have it .. near perfect idle and running conditions in every regard!

In regards to the spider, we determined it was coming from the fuel pump. The pump is malfunctioning and making an extremely loud howling and screaming noise which was reverberating up the metal fuel line into the spider and making it vibrate. This is why it sounded like it was coming from the spider when the hood was popped. Im VERY surprised the pump is screwing up as its only 2.5 months old! Its a Delphi and well, looks like its a lemon. It is however maintaining proper pressure to drive great but, the scream it makes prior to start up is not a good sign. Very strange but nonetheless, finally figured everything out!

 

When you say "Temp Sensor" are you referring to the Intake Air Temperature Sensor?