TBI Throttle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.

Help! Canít drive after TB rebuild

Old 01-07-2019, 08:40 AM
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Help! Canít drive after TB rebuild

i recently rebuilt the TB on my 1990 5.0 TBI IROC. Itís new to me and has a massive vacuum leak causing a very high idle. I can hear the leak so loud it over powers the engine noise. I recently changed the fuel injectors so those are brand new. I rebuilt the throttle body with the exception of the electronics (relatively new) and the fuel regulator. Reinstalled and now the idle has reached the point the brakes barely hold (approx. 2500rpm tach is broke) this is my DD so I canít have this continue. Any any help is appreciated.

Slice
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Old 01-07-2019, 11:39 AM
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Re: Help! Canít drive after TB rebuild

Get a can of carb cleaner or brake clean or something, with it running, spray around the TBI, intake, brake booster hose, and every vacuum source. when the high idle dies down for a sec or gets worse for a sec, you have found the spot. Check the TBI mounting gaskets, PCV, etc.
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Old 01-07-2019, 04:53 PM
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Re: Help! Canít drive after TB rebuild

Could be that the IAC has been damaged and isn't closing. Or the gasket that goes on top of the intake under the TBI unit is dried out.

Also, did you lightly blip the throttle? Did you shut off and restart the engine after that? The ECM does an IAC reset at key-off.

RBob.
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Old 01-07-2019, 09:50 PM
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Re: Help! Canít drive after TB rebuild

I blipped the throttle a couple times, and restarted it. No change. The gaskets are brand new as I rebuilt it the night before. The leaking injector is causing a pretty big pool of fuel. What could be causing that? They have 60 miles on them total.
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Old 01-07-2019, 10:03 PM
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Re: Help! Canít drive after TB rebuild

One of the injectors leaking sounds like one of those little rubber o rings in the injector pod is torn. Where is the fuel puddling?
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Old 01-08-2019, 05:43 AM
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Re: Help! Canít drive after TB rebuild

Itís pooling right on top of the TB blade. I just donít understand why al of a sudden it would start doing this. I didnít touch the injectors or that part of the TB since I just changed them. Iíll check the resistance on it today, 16 ohms right?
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Old 01-08-2019, 09:25 AM
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Re: Help! Canít drive after TB rebuild

1.2 ohms.

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Old 01-08-2019, 11:05 AM
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Re: Help! Canít drive after TB rebuild

Originally Posted by Firebirdwade View Post
Get a can of carb cleaner or brake clean or something, with it running, spray around the TBI, intake, brake booster hose, and every vacuum source. when the high idle dies down for a sec or gets worse for a sec, you have found the spot. Check the TBI mounting gaskets, PCV, etc.
1. Brake cleaner is often WORTHLESS for finding vacuum leaks, as some formulations are not flammable. Other formulations will burn, but produce poisonous gas that can land you in the hospital with permanent damage. Similarly, don't use brake cleaner to de-grease metal before welding--when the stuff burns from welding heat, you can be poisoned.

2. Aerosol carb cleaner can be very helpful for locating vacuum leaks, but the usual result of spraying flammable carb cleaner on a vacuum leak (which typically makes the engine run lean) is that the idle speed INCREASES. Some guys prefer propane, with about the same results--often the idle speed goes up, not down. ANY repeatable change in idle speed that can be attributed to extra fuel (carb spray, propane, whatever) is likely evidence of the vacuum leak.

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Old 01-08-2019, 08:54 PM
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Re: Help! Canít drive after TB rebuild

Alright so I checked the o-rings for the fuel injectors since nothing else made sense for a leaking injector since they tested at 1.5 ohms. Come to find the leaker has a small foam o-ring installed and the good one has a rubber one (both the small o-rings). Swap out with spares that I had and no more leak. Starts up no leaking good to go, right?

well I heard a leak around the TB base so I checked the torque on the TB and sure enough the gasket had compressed and they werenít tight. Torque appropriately and now it wonít start. No fuel it seems. I had this problem before and I though I had it figured out but now I wonder if it was coincidence. Thinking fuel pressure regulator as I can hear the pump running.

I will Iíll do some testing tomorrow and let you know what else I find. Thanks all

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Old 01-08-2019, 11:00 PM
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Re: Help! Canít drive after TB rebuild

Oh yeah, I'd only use brake clean if nothing else was available, and still never the chlorinated stuff. Ironically, you really have to keep the "non-flammable" brake clean away from heat so you don't gas yourself.
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Old 01-09-2019, 08:15 AM
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Re: Help! Canít drive after TB rebuild

BrakeKleen in the green can is mostly acetone and methanol. This stuff is flammable and is safe to use around heat & UV.

BrakeKleen in the red can is very dangerous around welding. As mentioned it is a chlorinated solvent. When stick welding, or MIG or TIG with CO2 shield gas it creates phosgene gas. Bad stuff that can kill you (think WW1 chemical attacks).

If welding with argon shield gas it gets even worse as it creates hydrogen cyanide. That stuff can kill you in a matter of seconds.

Since from time to time I do welding the red can solvent is not even on the property, anywhere. Green can only for me.

As for finding vacuum leaks a smoke machine works wonders.

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Old 01-09-2019, 08:35 AM
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Re: Help! Canít drive after TB rebuild

I think there are a few different kinds of tbi gaskets. Make sure that you have the right one because some are shaped a tiny bit different and don't cover the whole base.
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Old 01-09-2019, 08:44 PM
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Re: Help! Canít drive after TB rebuild

So I bought a throttle body rebuild kit that cane with several additional gaskets. I picked the thick one since that is what came off the car but sure enough it isnít the same shape. Iíll be changing that out ASAP. Would this keep the car from starting? It stumbles and then quits. I got it to run twice and it was at 2300 rpm in park.
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Old 01-10-2019, 07:23 PM
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Re: Help! Canít drive after TB rebuild

Alrighty, thanks for all the help thus far. I swapped in the correct shape throttle body gasket. I also in the process broke every hard vacuum line that came off the engine except to the Evap canister. I replaced all with new except for the one for the HVAC, which I capped. I was able to get it started with starter fluid and would you believe it, it ran at 740 RPMs, HALF of what it was before. Iíll deal with the cold for a while as long as she runs.

But, and thereís always a bit right, I am not getting fuel at start up again. Itíll start with starter fluid and then run smooth but I get nothing from the injectors prior to that. New injectors, and I swapped the relay with the AC one previously and there was no change (AC works fine), new fuel filter, I can hear the fuel pump prime the fuel line. it did this when I got it last month but then it stopped. Could the pressure regulator be bad? Iím afraid if I keep using starter fluid I could do damage to the valves or something.
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Old 01-11-2019, 10:08 AM
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Re: Help! Canít drive after TB rebuild

A few things to check:
1. Car off, move key to on position (not crank) do you hear the fuel pump prime? If yes skip 2.
2. If no prime and the car cranks with primer fuel or starter fluid and continues to run on the fuel pump then there is an issue with the circuit. The oil pressure sensor also enables the fuel pump and will run it in this situation. If this is the cause its likely the voltage, ground, or wiring for the fuel pump at the ECU. I can give you more details here if this is the case. Also could be low fuel in the tank.
3. if your fuel system is priming and it will start on starter fluid and then keep running then either the injectors are gummed up and will not start squirting under initial primer pressure but will under full run pressure. Or you don't have enough fuel pressure at prime (a leak, air in the line, bad fuel pump, bad regulator, bad filter etc). A ohm test will not tell you this. I had this happen and new injectors solved it. Also low fuel can cause this so make sure you have at least a 1/4 tank, don't fill the tank encase it is the pump.

\if you don't want to fix properly you can hotwire you fuel pump and it will crank, before I replaced my injectors I had a button I would hold down to force the pump on continuously so I could crank it... LOL that was in college over a decade ago so the cheap solution right...

Since it was cranking with the leaking o-ring I'm going to say you are looking at 3 since the leak was starting the car and then you had enough pressure for the injectors to fire. You can get new injectors pretty cheaply.

This reminds me since I've swapped engines I need to list my TBI for sale Unfortunately there isn't a pressure port on the car you have to buy an adapter that goes inline and its a PIA to get on. But I would check pressure before dropping the tank for a new fuel pump.

Last edited by Aviator857; 01-11-2019 at 10:16 AM.
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Old 01-12-2019, 07:00 AM
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Re: Help! Canít drive after TB rebuild

Brand new injectors just put in last month. That I thought solved the problem but it has since resurrected itself. Fuel pump does prime the line so fuel pressure from the pump or the regulator are potential caused then? I also read a thread where someone had identical symptoms and it was the magnetic pickup in the distributor that caused it. I think I need to check the fuel pressure first though. Did you connect a gauge underneath the car? I canít see where I would be able to put a gauge inline in the engine bay.

Strangely, if you get the car running you can usually go start it again without starter fluid within a few hours. Itís almost like once it warms up the problem tends to go away.

Last edited by SliceIROCZ; 01-12-2019 at 07:03 AM.
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Old 01-12-2019, 08:17 AM
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Re: Help! Canít drive after TB rebuild

How old is your fuel? If it's old and varnished it can cause the injectors to stick pretty fast. Were they new or rebuilt injectors? Name brand or eBay specials?

The pressure tester I have has a T adapter that goes between throttle body and the hard line. It's a pain to get on.

If magnetic pick up I wouldn't think it would keep running after starting it with starter fluid... Could be wrong though.

Put a test light on fuel pump relay and see if it's running the pump during cranking. If it is I would not think it was electic issue. If you run the starter log enough you can build enough oil pressure and that circuit takes over and enables the pump.
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Old 01-13-2019, 09:38 PM
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Re: Help! Canít drive after TB rebuild

Fuel should be pretty good. I filled it with new gas from low before doing the injector/filter change. This was also when the symptoms went away and I thought I had figured it out. Fuel injectors are Reman from Autozone I forgot the brand. Injectors look vastly better than the ones I removed and now have a decent spray cone.

Iíll go back and reread the thread where they determined it was the magnetic pickup but it sounded a lot like the same issue.

I have to find a fuel pressure gauge to see if the line is being primed to the right pressure. Iím leaning towards that but I just canít figure out why the problem
goes away once it has warmed up.
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