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TBI driveability issue

Update...

I installed a brand new fuel pump and fuel filter on the K5, as well as, the brand new IAC, and a brand new tbi base gasket.

The brand new tbi base gasket fixed the high idle problem, but the blazer still runs the same going down the road.....runs like crap - way under powered!

I have my brother's GM Tech 1 scan tool, but apparently it doesn't have the mode to check the TPS voltage......grrr

No improvement whatsoever for any speed going down the road.

The blazer doesn't buck, snort, backfire, etc, it just doesn't have the normal power of a tbi 350 motor with 4.10 gears and 35" tires like on my other blazers and pickups that had the tbi 350 in them. It doesn't pump out black exhaust like if it was running rich either.

Tomorrow I'll check the TPS voltage with a VOM and see what it comes with.
 
Come on? A tech 1 can't read TPS? This was GM scan tool for these systems...

And my $300. AutoXray Scantool will? And also do any car up to 2010...

You sure? Anyway DVM will! Hope it's your issue.

Does it read MPH from VSS?

Have you checked to see if your skinny pedal makes the throttle blades go WOT?
 
Well that's what I would've thought too, but I didn't see it in the menu on the little screen.

Without popping the hood again, is there 2 or 3 wires that go to the TPS connector? If it's 3, which wires do you test the TPS to check it for voltage?

I don't see a spot in the menu on the Tech 1 to check it for MPH from the VSS either.

I haven't checked yet to see if full throttle at the pedal is opening the throttle plates all the way or not. I will tomorrow after work when my friend that I used to turn wrenches with at a shop, is coming over to take a look at it with me.
 
What does it do? Nevermind I don't want to know, I thought it was a good tool...

TPS has 3 wires. Probably these colors, if not positions will be the same.
A Black is ground
B Dark Blue TPS signal
C Grey 5 volt reference signal

Ground DVM does not have to be to A, can be to motor. Probe B with positive end of DVM. With key on it should read about .54 volts, open throttle slowly and the reading should go up smoothly to about 5 volts WOT. If so? TPS is good.
 
It had been since 2000 since I touched a GM Tech 1 tool and yes it does have lots more data to get off it.

Had to push the No button to get it to scroll down the data list.....:haha:

Anyway, with the Tech 1 the TPS is at 0.64 volts at idle and at 4.10 at full throttle.

My buddy came over and with the throttle pedal pushed to the floor, the throttle plates only opened up to 1/2 throttle.

So we bent the OEM throttle cable bracket back towards the rear some more, and then moved the throttle cable to the pin for the cruise control cable (no cruise control on this K5).

Now it's getting full throttle at the throttle plates....:thumb:

But the throttle pedal is stiff and there are no return springs on the linkage either.

My next step is to replace the tbi unit with another known good one. I just bought a 88 Burb tbi 350 complete with wiring harness, ECM, pan to air cleaner, 31 gal gas tank, fuel sending unit, dash cluster, bezel, etc.

I bought anything I want off it (minus front and rear axles and the radiator) for $450. My coworker had the Burb and drove it every day to work and back home. It never smoked, burnt oil, and it ran great. Another friend of mine bought it for the 700r4, the NP 208 t case, axles, and radiator.

So it looks like I'll have it fixed as soon as I get the other parts.

Thanks for all the help......:thumb:
 
:doah:

You sure it's the TBI that is making it hard to depress? Disconnect it and try the TBI and throttle linkage/cable.

Most TBI have 2 springs on them wrapped around the throttle shaft. I have been known to cut one on conversions! Stock trucks that came with TBI had proper linkage for all that spring.
 
As a temp fix until I get the other motor and tbi, can I use a good tbi from a 5.0 if I put my injectors in it? Or is the 305 tbi smaller in cfm rating? I already have a nice tbi from a 91 5.0 tbi trans am.
 
I swapped the motor out for the 88 TBI 350 that was in my coworker's 88 Burb. I used the throttle body from the Burb as it was a known good working, problem free unit.

It turned out to be a GM "New 350" crate motor after wiping the crud off the GM valve covers and finding the GM decals on it.

The Blazer runs better then it ever has since I got it, but it still dies when I first fire it up unless I hold the throttle pedal down to keep it idling for a couple minutes.

Before the engine swap, my Blazer has always died at cold startup but I'm thinking it's because I might not have a full 12v signal coming up to my alternator. I swapped out the old alternator with the one from the 88 Burb when I swapped the motor, and it still acts the same.

So my next test will be to see if I have 12 v coming up to the 2 pin plug on the alternator and at the bat post on the alternator. I'm wondering if a blown fusible link is the culprit down by the starter? The only way the alternator will charge is if I give the motor some rpms, but it did the same exact thing as the old alternator, so I'm leaning towards something else being the problem.

The bottom end and mid-range feels like a normal TBI motored Blazer now, but the top end is still a little weak feeling to me. Could it be because I have stock manifolds going to dual 2 1/4" exhaust pipes with Flowmaster mufflers and tail pipes with no Cats, vs a single 3" pipe from the y pipe to the muffler and then a 3" tail pipe? A single 3" pipe is what I had on my 87 K20 4x4 and my 89 K5 and they both ran awesome with that setup.

Thanks for all the great help you guys provide.

Doug
 
Silverado_K5 said:
The Blazer runs better then it ever has since I got it, but it still dies when I first fire it up unless I hold the throttle pedal down to keep it idling for a couple minutes.

Before the engine swap, my Blazer has always died at cold startup but I'm thinking it's because I might not have a full 12v signal coming up to my alternator. I swapped out the old alternator with the one from the 88 Burb when I swapped the motor, and it still acts the same.

So my next test will be to see if I have 12 v coming up to the 2 pin plug on the alternator and at the bat post on the alternator. I'm wondering if a blown fusible link is the culprit down by the starter? The only way the alternator will charge is if I give the motor some rpms, but it did the same exact thing as the old alternator, so I'm leaning towards something else being the problem.

The bottom end and mid-range feels like a normal TBI motored Blazer now, but the top end is still a little weak feeling to me. Could it be because I have stock manifolds going to dual 2 1/4" exhaust pipes with Flowmaster mufflers and tail pipes with no Cats, vs a single 3" pipe from the y pipe to the muffler and then a 3" tail pipe? A single 3" pipe is what I had on my 87 K20 4x4 and my 89 K5 and they both ran awesome with that setup.

Thanks for all the great help you guys provide.

Doug
Click to expand...
Could just be your butt dyno is off? Or are you comparing stock gears and tires to stock gears and bigger tires or?

If the fusable link was blown it would never work.

So you got a new motor, it's better, but cold start is still and issue? EFI has got to have good 12 volt power, you got the new altenator which should charge better at low RPM which EFI needs. Is your battery weak? Cranking takes a lot of power from a battery, then may be low till gets charged? Voltage low also makes fuel pump voltage low which makes pressure low... did you use the ECM from new motor truck? :confused:
 
It's been so foggy here lately with freezing fog, that I haven't had a chance to look at the Blazer.

I do have the ECM from the 88 Burb, and I will install it in the Blazer this week to see if it changes anything.

The wiring up to the Alternator and changing the ECM was my next steps to do.
 
Quick test would be check battery voltage before you start, watch voltage when starting and see where it is when it first starts running?

You changed engine to a truck that was converted and runs better, but still have same issue at startup makes me think it is in the truck...
 
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