TBI 454 lacks power

[roundhouse]

We installed the fuel pressure gauge tee and ran a hose some could zip tie it to a windshield wiper

That way we could see it and if it dripped a little it was outside the cab


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[Dr_Snooz]

I fiddled with my HF adapter today and was able to get it to seal. Fuel pressure was 11.5 psi at all times under all conditions, including hard throttle, up a hill, towing my tool trailer. The fuel filter is not clogged.

I'm flummoxed.

[bd]

Assuming the vehicle displayed symptoms during your road check, the fuel pressure is okay.  Did you check exhaust backpressure with a gauge as previously suggested?

[Dr_Snooz]

It was displaying symptoms on the road test. I haven't checked the back pressure yet. It's next on my list.

[Irish_Alley]

dual tanks?

[Dr_Snooz]

Single tank.

Since we're getting to the outlier possibilities, I thought of a couple possibilities last night. First, when I pulled the engine the injectors were hard wired to the loom. There was no Molex-type connector between the injectors and the loom. When I pulled the engine, I had to cut the wires. When I put it back together, I wired in a cheap Molex-type connector from Radio Shack. The connector I used looks more like the connector you'd find on the fan inside your computer than what you'd find under the hood. In other words, it's not really the right connector to use. It makes good contact and is not corroded. In my research, I wasn't able to find that injectors are very picky about voltage drops or amperage draws or anything that could be related to that connector, so I can't think of any reason why it would be causing problems. Nevertheless, there's always that possibility. Anyone have thoughts or experience on that? If the connector is no good, how do I reconnect those wires better? My preference is to have a proper Molex-type connector rather than butt crimps or wire nuts or something.

Second, the catalytic converter is only two years old. My smog test was last month and the numbers were epic. It ran super clean, so I know the cat works well. However, upon first start of the new engine, I got gallons of water blowing out the tailpipe. It did this solidly for two days and then tapered off in the next week. Now it doesn't do it at all. I speculate that the tailpipe filled with condensation during the month I had the engine out and the pipes open. The shed in which the truck was sitting had a lot of condensation dripping from the tin roof during that time and some of it could have fallen in. It seems very unlikely that all that water came from a dripping roof, but that's the only thing I can think of. The question is whether all that water blocked the exhaust flow somehow?

I'm just brainstorming here. I know. TLDR.

[bd]

What do you mean the injectors were "hard wired?"  The injector harness should be terminated with this.  Post a pic.  Nonetheless, the Molex connector shouldn't cause an issue as long as the wires were clean and crimped properly to their terminals.

Is the radiator coolant level low?  If it is, run a compression check.  Otherwise, check the exhaust backpressure.

Be careful about reaching for wild conclusions!  Proper diagnosis is systematic and methodical.

[Dr_Snooz]

Yeah, those are the connectors. Unfortunately, the wires coming off them go through a small hole in the aluminum throttle body, then disappear into the loom. There's no way to remove them without cutting them.  

Coolant level is fine. Doesn't leak. Doesn't smoke.

I might buy one of those ALDL cables so I can monitor the sensors in real time and see what's going on when it loses power.

I'm trying to scare up a backpressure tester locally. I checked spark voltage today based on someone else's recommendation and it's 30kV, so that checks okay too.

[Dr_Snooz]

I swear I typed up this post a few days ago, but I guess it didn't take. I can't find an exhaust pressure tester locally and I don't want to send away for one, so I threw my vacuum gauge on the truck the other day. With an exhaust restriction, the vacuum should fall off at higher revs. Mine stayed steady, which is what it's supposed to do. My cat is just over 2 years old and the truck passed its smog check two months ago with flying colors. I mean, the emissions levels were amazingly low. I don't think I have a clog, but if you guys think I should buy the gauge to confirm, let me know.

In other news, I replaced the PCV valve for kicks and the situation is noticeably improved. Not 100%, but better. So I'm thinking vacuum leak? Any suggestions for spotting vacuum leaks aside from the spray carb cleaner deal?

[bd]

Don't buy a backpressure gauge.  Does your vacuum gauge also register pressure?  At ~2000 RPM, exhaust pressure should measure no more than 1.5 - 2 PSI.

[Dr_Snooz]

Well, the truck is running better and better with that new PCV. Tonight coming home it was almost normal. I unplugged the battery to reset the ECM and clear out the old maps when I got home. We'll see how it runs tomorrow. I might have solved my problem.

[bd]

Spray a little B12 through the PCV and down the throats of the throttle base to see if that makes any improvement.  Then pull the vacuum line off the MAP sensor and do the same to wash out the line all the way into the TBI base.  Could be as simple as carbon building up under the base, restricting vacuum signals.

[Dr_Snooz]

It was a fun couple days, but now it's worse than before. Aaaarrgh.

I'll try cleaning the vacuum lines next.

[Dr_Snooz]

Getting back to this after a long absence. This problem is ongoing and exasperating enough that I just want to sell the truck. Too bad that it's all set up for me: overload springs, wiring to run the camper, trans cooler, oil cooler, battery isolator, inverter, etc. So I soldier on.

I found in the GM manual a troubleshooting section devoted to low power complaints. It's pretty thorough covering:

- check air fiter
- check timing
- check condition of plugs, wires, all vacuum lines
- check EGR operation
- check for silicone contaminated O2 sensor
- check exhaust backpressure (using a vacuum gauge)
- check compression
- check valve timing (ie: timing chain/cam problems)

I followed the procedure, checking everything right up until check compression, timing chain and other things gone horribly wrong with a rebuild. So far, everything checks out great. Plugs show signs of maybe running a little lean, but nothing that would completely emasculate my truck, I think. The O2 sensor looks good to me, but I'm no expert.

Pics are below and second opinions welcome. (Okay, there's only 7 plug pics because I'm an idiot. Suffice it to say that they all look the same.)



















Anyway, when I connected my vacuum gauge to do the backpressure test, I noticed that the needle whipped erratically around ~19Hg. As I increased the throttle, it whipped erratically over a much wider range. From what I can research, this indicates weak valve springs. I'll try to get a video of the gauge later today, but would weak springs cause a low power problem with a rough and surging idle? I assume it would. If I have valve problems, then it's something I need to take up with the rebuilder, right? How hard is it to change valve springs?

[bd]

The spark plugs appear fine, although from the color change on the ground electrode, they are burning a little hot.  You might consider changing to an AC R43CTS next tune up.  The condition of an O₂ sensor cannot be judged by appearance, only by monitoring its function with a scanner.

I am curious...

...when I connected my vacuum gauge to do the backpressure test, I noticed that the needle whipped erratically around ~19Hg. As I increased the throttle, it whipped erratically over a much wider range. From what I can research, this indicates weak valve springs. I'll try to get a video of the gauge later today, but would weak springs cause a low power problem with a rough and surging idle? I assume it would....

Were you trying to check exhaust backpressure?