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Old 01-02-2013, 10:03 PM
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throttle blip causes bog

I have a 1990 454ss but currently it has a throttle body injected 350.
So whenever I blip the throttle the engine bogs and will die if held. I can open the throttle smoothly and the engine will rev. Depending on how I blip the throttle and fether it, the engine will backfire. No matter how fast the engine is turning if I blip the throttle it bogs.

Here is what I've done:
-Cheked plug wires are correct
-plug wires are good
-has a new distributor and ignition coil (replaced to get it running)
-timming is good.
-if the TPS is disconected nothing changes, took it off and left conescted, and no difference. Moved the TPS manually without throttle movement and this does nothing (no I havnt researched all the details on what this unit does)
-Tried a different MAP sensor
-NO vacuum leaks.
-If I disconect the vacuum hose from the MAP sensor the engine runs like a POS but if I blip the throttle it doesn't bog.
-intake doesnt leak
-throttle body is sealed
-injectors are clean

I know I can hook up a code reader and diagnose this but I dont have one and cant bring it in to a shop. Just looking for some help before I spend money on a code reader and parts if I dont need them.

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Old 01-02-2013, 10:22 PM
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forgot to mention I had the timmoing light hooked up just to watch the spark and when the throttle is blipped the timming seams to cut out no matter which wire its on. Cut out as in the light quits flashing momentarily
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Old 01-03-2013, 09:42 AM
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Originally Posted by KMPJ-93 View Post
forgot to mention I had the timmoing light hooked up just to watch the spark and when the throttle is blipped the timming seams to cut out no matter which wire its on. Cut out as in the light quits flashing momentarily
Thats a strange one. have you tried to put a battery charger on the car and try thte blip.

Spark should not drop when the throttle is touched. No real connection between the systems. What type of dizzy. HEI can do all kinds fo strange things with low voltage or bad coil or moduale. Best to check the system over and make sure the cap and rotor are not cracked or broken any where. also make sure the wires going to the distributor are not touching anything when the engine moves for stepping on the gas. Might just be a bad wire grounding out when you hit the gas. also be sure the ignition is using thick strong car type wire and does not have some speaker wire running for power. Need thick wire that will not melt when it gets hot.

USally this type of problem is from the power wire touching the header or manifolds but can be in the back of the engine as well.
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Old 01-03-2013, 09:51 AM
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Is this a bone stock 350 with the 350 TBI unit, 350 harness, and 350 computer?

Or are some of the parts from the 454?
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Old 01-03-2013, 04:44 PM
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The engine sounds camed, and has shorttube headers. Other than that it seems stock. I assume the electronics are for the 350 as I have extra electronis in a box of 454 parts. New distributor (including cap/rotor) and ignition coil. I don't believe this unit is HEI as it's not the big cap with power wires etc. going to it.

I never thought to check the voltage of the battery/load test, I just charged it and put it in. I will check for rubbing wires in the back.

Are you recomending I take off and clean all the grounds? (I know I shoud probably do this anyways)
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Old 01-03-2013, 04:53 PM
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Quote:
Originally Posted by KMPJ-93 View Post
The engine sounds camed, and has shorttube headers. Other than that it seems stock. I assume the electronics are for the 350 as I have extra electronis in a box of 454 parts. New distributor (including cap/rotor) and ignition coil. I don't believe this unit is HEI as it's not the big cap with power wires etc. going to it.

I never thought to check the voltage of the battery/load test, I just charged it and put it in. I will check for rubbing wires in the back.

Are you recomending I take off and clean all the grounds? (I know I shoud probably do this anyways)
Yeah clean grounds are always a must. If its efi i would check the main harness grounds for corrotion. The battery, fuel rail, behind the engine does it have a grounding strap going from the engine to the frame. And is the computer bolted down and grounded.
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Old 01-03-2013, 09:49 PM
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I cleaned all the grounds, and everything is bolted down properly. The issue still remains.

So about what I mentioned about the MAP sensor. When I disconect the vacuum line, it runs terrible but the bogging issue seems to go away when I blip the throttle. I'm pretty sure the MAP sensor is good, but like I said I don't have a code reader.

does the MAP sensore just run off the vacuum? what does the MAP sensor control or does it run in sync with other sensors etc.?
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Old 01-06-2013, 08:11 PM
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Here's an update on the bogging issue I have. I've been heading in the right dirrection.

First off, for older vehicles like this (not sure maybe even all OBD1) a scan tool is NOT required. All you need to do is jump "terminal B" to the ground terminal (i can go into deatail if anyone would like). With these terminals jumped and the ignition on (vehicle not running) the vehicle goes into diagnostics mode and the "SERVICE ENGINE SOON" light begins flashing in sequences. It flashes once, pauses, then flashes twice consecutively (code 12). It does this three times, then flashes the codes. the way it flashes creates a number. EG: flash pause flash flash flash, means 13.

Anyways all I got was code 14, 15, and possibly 16 (did 5 quick flashes then a small pause before the last) Code 14 and 15 have to do with the temp sensor, and 16 has to do with a speed sensor I believe. None of these have to do with an ignition issue so I went on diagnosing sensors manually.

Basically the only left to be tested was the IAC valve. While the engine was running I disconected the IAC and nothing happened (I believe it should rev up?). So I took out the IAC and cleaned it. The haynes manual said the thing inside should not stick out more then 1-1/8" so i made it a bit less and re-intalled it. According to the Haynes manual, ECM will reset the IAC valve once the engine reaches operating temp. and is shut off. When I fired up the engine it idle reaaaallly high and backfired alot and would still bog when the throttle was bliped. But I waited for it to reach operating temp., shut it off, and fired it up again.
Nothing changed, and it was still idleing high, so to me this means the IAC valve did not reset, and is faulty. I pulled the IAC valve again and did an OHM test...55ohms, is that alright?

I then ran the truck without the IAC valve in it, and the wires disconected. It idled high and rich as hell, but when the throtle was bliped it reved right up with no bog.

So I am thinking the IAC valve is my issue. Or perhaps the ECM is not reading the sensors properly. I find it wired that nothing is throwing codes. But any further input would be great.
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Old 01-06-2013, 09:25 PM
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Maybe a foolish suggestion but try changing the fuel filter. Sometimes this can cause a drop in fuel pressure and cause a lean condition.
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Old 01-06-2013, 09:33 PM
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Thank you for the suggestion, but i have a new one in already.

But I think I answered my own question

ENGINE COOLANT SENSOR. Code 14 and 15. I had a brain fart. When i read engine coolant sensor I thought to myslef "duh...my temp guage is working fine"....but thats a different unit in itself.

The engine coolant sensor tells the PCM if the engine is cold, warming up, normal, or overheating. It plays a role in timming as well as a whole schwack of stuff. Tomorrow I will get a new one, and post back with my results.
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