94 5.7 TBI Intermittent loss of power towing uphill - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 02-09-2011, 06:50 PM   #1 (permalink)
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94 5.7 TBI Intermittent loss of power towing uphill

I know it is tough to diagnose ANY problems without a) being there or b) having the computer data...but l need some suggestions.


1994 C2500 Ex cab TBI 5.7/4l80e.

Truck is in Seattle (parents rig).

When pulling 2 horse trailer w or w/o horse...up hill...truck lacks power and falls on its face. Sometimes you can let up of the gas pedal and then hit it again and it clears right up and runs fine. You can take the same route over and over and it does NOT do it all the time. Truck will downshift to lower gears but acts as if it is 'cutting out' as described to me by parents. Seems to do it on the 'return trip' from horseback riding...not on the way there.

Unloaded NO problems at all.

Truck taken in to local repair shop. These items were found to be "faulty" and repaired/replaced.

TCC solenoid
EGR Valve
Fuel pump
Fuel Filter replaced as well.

ALLEGEDLY these things below have checked out OK.
O2 sensor
Coolant Temp sensor
Fuel pressure...not sure where checked...if it was after regulator or not.
Tank looked clean...no debris

Wondering where to go from here. Tried to explain to my father in law that they need to run winALDL and capture the tables to see what is up. Each time it goes to the shop and THEY drive it...it does not 'act up'. Not sure if this particular shop is well versed in TBI or not. After the truck came back from the shop the last time it is now slow to warm up...but does come up to temp...used to warm up pretty fast.

Have SEARCHERD and found that the regulator could be bad...not sure if they checked that or not, ignition issue with the distributor, map sensor, TPS (again allegedly ok).

It is hard to get the parents to ask the 'right questions' and get the right answers. I may need to call the shop myself and see WTF is going on.

Anyone else tried and successfully tracked down a low power issue under load with a TBI?

Cliff notes.

Parents 94 c2500 TBI 350
Sometimes moves as fast as Jabba the Hut when under load going up hill.
Local shop can't seem to find problem, some issues fixed but still happens
Came to Pirate for help...
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Old 02-09-2011, 07:05 PM   #2 (permalink)
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Quote:
Originally Posted by oldschoolrides View Post
Sounds like a possible bad injector.
I Googled that and did not find a ton of info...but it does sound plausible. I will try to look that up some more..

I asked my step dad to go out and with a timing light shine it on the injectors and see if he could see them dribble at all...and what the pattern looked like...and to see if they drip when turning it off.

Interesting thing is that truck with trailer runs fine on the flat...up hill with a load...it sometimes shits the bed. Does not die...but lacks power 'sometimes'...today he told me when he was driving it it was like it was lacking fuel.

Oh yeah...only 80K on this engine (original).
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Old 02-09-2011, 07:19 PM   #3 (permalink)
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Found this thread...about the same issues...except that parents truck runs and idles fine. Again "allegedly" the shop has checked this stuff...maybe time for a new shop!?
-----
1987 Suburban, 350, 700r4, stock GM crate motor with about 30k on it. When I put the motor in about five years ago it ran great, until recently.

After searching, learning, and testing different components this what I got.

Symptoms:

• Seems to run OK when cold but not what it should.
• Erratic idle.
• Idle is worse when in drive opposed to being in park.
• Lacks power and seems to “cut out” when under a load. I first thought it was hunting for a gear but not so.
• All of this has gotten worse over about 3 months to the point of I really cant drive it any more.

I cleared the codes and drove it for a day then checked them, this is what I got:

• 24 Vehicle speed sensor. My speedo works fine, I don’t know what this is.
• 44 O2 sensor lean condition. Not enough fuel?

Conclusion 4/24/09 If you don't want to read this whole post here are the findings:

1) Bad vss.
2) Vacuum leak between the TBI and intake manifold.
3) Bad plug wires, they were arcing to the engine block.


--------------------
Father in law says plug wires were replaced last year...possible that they are worn or bad...should have him go out and look for any blue arcing at night...

Humm...I guess that i better call the shop and get the full details on my parents ride...and use the above as information to question WTH they are doing. LOL Anyone else ??
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Old 02-09-2011, 07:20 PM   #4 (permalink)
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How about the evap system, has it been checked to see if there is any restrictions in it or the fuel return lines? Maybe the fuel pressure regulator too. Going uphill with higher fuel demand may cause a faulty regulator to crap out.
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Old 02-09-2011, 07:30 PM   #5 (permalink)
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Quote:
Originally Posted by just4cuz View Post
How about the evap system, has it been checked to see if there is any restrictions in it or the fuel return lines? Maybe the fuel pressure regulator too. Going uphill with higher fuel demand may cause a faulty regulator to crap out.
EVAP...that is something I mentioned to father in law...but doubt he asked the shop. One would figure that they would check this shit...if they knew what was up.

As for the FOP regulator...not sure where they measured the FP at...in line with the filter removed..or the more PITA way at the TB itself. I agree...they need to check FP under load...but since it is an intermittent thing...could you really suspect the regulator?


Back to the EVAP...not sure what could cause the problems stated...will have to read up on that.

Thanks for the suggestions.

Keep bringing it...
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Old 02-10-2011, 04:42 AM   #6 (permalink)
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On my 92 I had an injector go out intermittently and have the same issues you are having. The injector would fail under load an after the truck had been running for a while. Cold days it ran fine. You best bet is winADL thats what I used. I seen in the logs when it started loose power is was running very very lean or richer than any saudi.
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Old 02-10-2011, 08:19 AM   #7 (permalink)
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Pull a spark plug. I'm betting that it'll be white as it sounds like the truck is running lean. Either way look at a spark plug. And while you've got the timing light on it (you said you were going to look at the injector spray pattern), look at the timing mark at idle. It should be advanced almost farther than the timing tab (WITH THE TAN WIRE CONNECTED). Open the throttle and the timing should advance even more, then "tap" the intake manifold with the handle of a screwdriver. The timing should retard momentarily. This will tell you if the ignition is behaving correctly. 90% of TBI issues are the fuel pump or the ICM.
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Old 02-10-2011, 04:13 PM   #8 (permalink)
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I had catalytic converter that would warp internally under load, causing a significant restriction in the exhaust system. The result was my Jeep couldn't get out of its own way. Gutted the Cat, and that solved the issue.
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