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89 suburban tbi issues

D

dick_landy

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Mar 17, 2007
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Location
winnipeg,manitoba,canada
Here is a run down on my truck:

5.7 tbi, injector spacer, k&n with extreme top, 2.5" dual exhaust from manifolds back, 40 series mufflers,35" tires with stock gearing, within the last few months I have replaced:

optima red top battery, o2, accel cap and rotor, msd wires,stock delco plugs, rebuilt the tbi inluding the injector o rings, fuel pressure is bang on, tps sensor, tbi base gasket,fuel filter, idler pulley and an a/c delete pulley kit.

The issue:

starts good, idles good,runs good, accelerates good. whats the problem you ask?Theproblem begins when the motor is warmed up, if I am driving very slow - for example in a parking lot or pulling out of a parking space, the motor begins to surge and run lopey like it has a huge cam. rarely it has done this while driving. If it has, it has been at around a steady 30mph with my foot barely being on the pedal. It has done this before and after replacing these parts.

Today I tried to make the truck run like that while in gear but holding the brake pedal. At idle, it runs smooth at 500rpm like its supposed to while in gear. Bring it up and hold it at 750rpm it starts to run rough although it rarely wants to die, it drops down to 500 then back to 750. Sometimes it drops to 200-300rpm and bounces back. Then if while in gear I bring the idle up to 900rpm, it will run perfectly smooth.

I will add that if I am cruising at around 45mph and up or I accelerate full throttle, when I let off the gas it smells heavily like gas(when the rear window is down).

Now I am thinking I need to replace the timing chain. Here is my theroy:

If the motor is under a hard load the timing chain has tension, when I let of the gas, the chain slacks up and retards the valvetrain slightly, therefore explaining the odour of gas. When the idle is at 750rpm in gear, there is a load but not quite enough to keep the tension on the chain all the time(tight,slack,tight,slack, in conjuction with when the motor fires). When I put a timing light on it, it was bouncing between 0 and -2 degrees.

This is starting to piss me off and I figured someone here can agree with me on the chain or point me in the right direction.

Thanks
 
Is it throwing any codes? You'll know if there are any codes if the service engine light is on. If it isn't on, maybe the bulb is burned out.
 
ran it on a snap on scanner, no codes and i dont think the bulb is burned out. a mechanic freind of mine says "0* is the "new vehicle" setting but they never run right when they are old and tired, we dont even put a light on them, we set the timing by ear"

seriously though, what else could it be? its got 260,000 k on it and i can guarentee its never been apart, doesnt run rich(tail pipes arent black) doesnt puff even when cold and doesnt use any fluids either.
 
What does the vacume look like at idle and 1000 rpm? Steady in the green or low and wobbly as if the ecm is hunting for the timing? Does the engine run beter under hard acceleration then moderate or the opposite?
 
Yeah I agree with you. Prolly is the timing chain. With that many miles on it I am sure it is definatly streched with worn gears. The timing jumping around a couple of degrees at idle with the bypass wire unplugged pretty much confirms it to me.
But before you tear it apart.

There is one other thing to check.... acually 2 The dist module and the magnetic pick up coil.
You can take the old module to an auto parts store. They can check it for you. Or buy a new one for 40 bucks.
There is a plug on the dist module with 2 wires connected.(white and green usually) These wires go the the mag pick up coil. Pull the plug and put an ohm meeter between the wires and read thru the coil. Should read between 500-1500 ohms. Check when the engine is warm if possible. if out of specs the coil is going bad.
Reaon I say is you said the problem starts after the engine is warmed up. Both of these components are affected by heat. When wearing out they start having problems after engine is warm.
 
havent checked vacuum yet to see what its doing, that would be my own fault,i will admit it slipped my mind. it runs fine under all other circumstances, hard throttle(other than the stench of gas when i let off), moderate, idle,cold or hot. its seems only when the throttle blades are slightly craked open.
 
Reaon I say is you said the problem starts after the engine is warmed up. Both of these components are affected by heat. When wearing out they start having problems after engine is warm.
Click to expand...

it wont do it because if the truck is cold its at fast idle until it warms up.its only around +1* celcius around here
 
Replace the thermal sensor in the front of the intake. Temp switch. You are flooding out. I would suggest that you get the one with the pigtail if your wires are worn at all. As a check, you can unplug the sensor and see if your problem goes away, or changes at all. I have replaced 5 or so of those sensors on various trucks for various problems.
 
I unplugged the sensor. The idle picked up from 700 to 900 rpm in park. the check engine light went on. I'm assuming the idle picked up because the ecu doesn't know that the engine is warm and it acts like the choke is on. Whats it supposed to do when I unplug it?
 
so i disconnected the vacuum line from the egr and plugged it and the problem is gone. now i know what to replace. thanks for all your suggestions guys
 
Check the EGR valve and controller. The ECM uses exhaust gas under 1500 rpm to lean the engine. If the EGR valve is sticking the ECM is flooding the engine and will cause a stall. That is why it only happens when the engine is warm and is allowed to idle down. Also check all vacumn hoses to controller.
 
There are varying parameters that invoke EGR, definitely not where the poster is having problems.

Make sure you aren't dealing with a simple vacuum leak, bad EGR solenoid, etc. before replacing the EGR itself. EGR's are fairly expensive to replace, especially if they aren't the problem. If it's not consistent, either the EGR isn't bad, or it's sticking ONLY after you've been cruising, etc.
 
Dick,

Did the EGR fix your problem?
I've got a 95 Yukon doing almost exactly the same thing!
I'd like to know how yours turned out.

-Ben
 
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