2oCHEVYo0

Okay, so I've posted in several forums and asked lots of people for advice only to stump EVERYONE! It's driving me NUTS!!!

WHAT I'VE REPLACED:
I just bought a new motor to put in my 1995 Chevy Silverado Z-71. It was purchased as a brand new (not rebuilt) direct replacement for this truck. I replaced the water pump, distributor, starter, wires, plugs, as well as the TPS, IAC valve and the coolant temp sensor located on the intake. Also the PCV valve has been replaced. I have spent a great deal of money and time on this swap and am very frustrated to not have a solid running truck.

NOW TO THE ISSUE:
The engine idles pretty good (700rpm) and can't really hear it having any difficulty. When I give it gas however it starts to bog down really bad and once you let off the gas it almost locks up for a bit and then jumps back to normal. The timing is good (4 degrees advanced) and it is not throwing any codes.

WHAT I'VE TRIED TO FIX IT:
I've swapped out the distributor three or four times between two new ones and the old one, and they all act the same. I then replaced the TPS and the IAC valve with no results. I also changed the coolant temp sensor. I have also ran sea foam through the whole motor and also changed out the fuel filter. I've also checked for vacuum leaks and never found one.

I spent ALOT of money on this project in hopes that I could start driving the truck and park the Camaro to start my real project, but this is taking LOTSSSS longer than I had hoped and draining all my maro's funds

Any input would be AWSOME as I seem to have hit a brick wall here

2oCHEVYo0

Any brilliant mechanics out there got any ideas? I'm so freakin lost

kevinkpk

I am not super hot on the 'newer Models" except getting my azz kicked with problems on my 96 Lumina. Does it use a MAF sensor? If so, get the correct cleaner for it, and try that. Also on your TPS check the reference voltage, I believe 5 volts with key on not running. Your saying distributer, and I assume hei. 4 deg (advance) sounds low at 700 rpm, but that should increase as rpm does, and dosen't sound like the problem unless it is not increasing with speed which would cause your problem. If you can get it to 2000 rpm, with a light check to see about where the timing is. The other thing, yea I know you checked for vacuum leaks, revisit that as an engine swap is prime culprit for one, and easy to miss. I'd also recommend with WD-40 in the areas that could have a vacuum leak.

2oCHEVYo0

It doesn't have a MAF sensor and the distributor isn't HEI. I have checked all the lines over pretty good and haven't found anything but I suppose I should do it again.

kevinkpk

So I assume it has a carb, and not fuel injection? I'd still try wd-40 with it running, and spray around suspect intake leaks, also if you have a vacuum guage see what it is at idle.

shamrock246

whats the fuel pressure?


Sean

97 4x4 burb

RacerX

Yea, is it carb'd or FI'd? I d say carb'd because in an FI system the TPS would give you that symptom. But you say you replaced the TPS. In a carb'd system the float or internal pump would give you a symptom like that if it couldnt keep up with demand.

Throttle body FI? Could be bad injectors also cant keep up with engine demand for fuel. Seafoam is good but not a cure all if you reused the same TB.



Then of course it could be a restricted fuel pump that cant match engine demand for fuel. Clogged fuel filter.

2oCHEVYo0

Well it's not a carb. I haven't checked the fuel pressure (hopefully tomorrow) but the fuel filter is brand new and it doesn't seem to have any problem with giving enough fuel. Had my dad take a look at her today and he seems to think it may not be cutting the fuel off quick enough when I let off the gas, thus, flooding the engine. It does seem to spray unburned gas out of the pipes when it starts bogging so it seems plausible to me. I'm gunna hopefully check the TPS tomorrow as well to make sure it's default voltage is correct.

RacerX

The way it is described it sounds like a flat spot in the voltage curve of the TPS. I had this symptom many times in many different cars when I had Fords. I had the problem 3 times in one car. The problem was at that time the TPS were aftermarkets(Wells, Borg-Warner, fake Motorcraft from Ebay) and then tines inside the sensor werent similar to the screw on the TB. So after a while the plastic tines would get chewed up by the screw. So I would open the throttle and the car would choke and then roar to life. Eventually got a Standard and the problem went away.

And you dont need to check the default voltage, you have to check the voltage as you work the butterfly KOEO. It should go from 0.5 to 4.5v real smooth. If it jumps or 0s out then there is a problem.

And another time it was the ECT sensor. The housing was plastic so it lowered/raised/whatever resistance and always put the car in a cold start mode.