Another 3.4 that won't rev over 3k-ish

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drodandsrod

New member
So the new rig has me scratching my head a bit. I just did the usual tune up stuff (plugs, pcv, air cleaner, maf clean, check and top up all fluids, fuel filter) and on the test drive I got on it a bit and it wouldn't rev over appx 3k. I checked in park and the engine won't free rev over 3k. No CEL and the engine seems to run well under the "rev limiter". I didn't find anything hokey during the tune up. I've searched all over for the last couple hours and I can't find a single instance where someone who describes a problem like mine posts finding/fixing the offending component. Are people just keeping it under 3k? FWIW I am a trained mechanic and I have read every post even remotely relating to this problem so I don't need answers like "check your plugs" or other shot-in-the-dark fixes. I'm looking for a definitive or experience/results based answer. Thanks for your input.
 
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Sounds like a limp home mode of some sort. Had a similar issue in my old vtech Honda. Throwing any codes?
 
I've had a 22RE do the exact same thing, and it was low fuel pressure. The hard line coming out of the tank had gotten crimped, so it would run fine at lower RPM, but as the fuel demand increased the pressure would drop because of the restriction.

I suspect that it was causing a lean condition and the ECU was pulling timing which made it feel like you'd hit a wall at 3500RPM.

I'd slap a fuel pressure gauge on it first thing, and at least then you can rule that out. It helps if you have one you can see while you're driving, so you can load it up and verify pressure stays steady.
 
I agree with above poster, if ECU thinks everything is fine and isn't throwing codes I would look at the fuel system, weak pump or bad filter.
 
Yeah, I guess I'll be looking at the fuel pressure. I'll have to see how much a fuel pressure test kit is gonna run me. I may just replace the pump, I just hate throwing parts at a problem though.
 
I had a 99 suburban 4x4 i was diagnosing with similar issues. No CEL. Idle perfect. Ran smooth up until about 3k rpm or if I put significant load going up ahill.

In that scenario it was short on fuel. It had the old spider injection system which was stupid and old. Anyway....I replace the injectors and injection controller and all was good.

If you don't have a plugged cat I would say fuel problem. Especially if the idle is spot on.
 
I don't know if the timing belt has been done recently in terms of miles. The lady I bought the truck from owned it for the last three years and put 2200 miles on it. I know she didn't have any maintenance done. Someone took care of it in the past though, I did the "new" vehicle tune up on it and there was even anti-seize on the spark plugs!

Funny you mention the 'burb and those crappy injectors. I had one too and had the same experience, just hadn't thought about it in a while. I'll likely just R&R the pump if I can't find a fuel pressure test kit. The idle is spot on, the exhaust does sound a little off but I chalked that up to my ear being tuned to V8.

Does anyone know the PN for the OE fuel pump?
 
Last edited:
drodandsrod said:
i don't know if the timing belt has been done recently in terms of miles. The lady i bought the truck from owned it for the last three years and put 2200 miles on it. I know she didn't have any maintenance done. Someone took care of it in the past though, i did the "new" vehicle tune up on it and there was even anti-seize on the spark plugs!

Funny you mention the 'burb and those crappy injectors. I had one too and had the same experience, just hadn't thought about it in a while. I'll likely just r&r the pump if i can't find a fuel pressure test kit. The idle is spot on, the exhaust does sound a little off but i chalked that up to my ear being tuned to v8.

does anyone know the pn for the oe fuel pump?
Click to expand...

950-0100

Denso 950 0100 Electric Fuel Pump | eBay
 
drodandsrod said:
I don't know if the timing belt has been done recently in terms of miles. The lady I bought the truck from owned it for the last three years and put 2200 miles on it. I know she didn't have any maintenance done. Someone took care of it in the past though, I did the "new" vehicle tune up on it and there was even anti-seize on the spark plugs!

Funny you mention the 'burb and those crappy injectors. I had one too and had the same experience, just hadn't thought about it in a while. I'll likely just R&R the pump if I can't find a fuel pressure test kit. The idle is spot on, the exhaust does sound a little off but I chalked that up to my ear being tuned to V8.

Does anyone know the PN for the OE fuel pump?
Click to expand...

I wouldn't start with the pump personally. There are other things that could be causing the problem. Your best bet is to check the fuel pressure before you start throwing parts at it. Could be the pump, or regulator, or clogged filter, or a kinked line, or some other odd issue we haven't mentioned yet. I've gone down this road and spent a lot of time and money for nothing.
 
Fixed

Well thanks for the input everyone. I finally got a scan tool and read through the stored codes. I had one for the TPS and one for the lockup solenoid. I did some looking and found that the lockup solenoid won't work properly without a good TPS signal. I replaced the TPS and life is good. The engine pulls cleanly and the trans seems function properly, so count me a happy camper.
 
I'm pretty sure the TPS was the issue. I'm not ruling out problems w/the cat at some point. For now though the engine pulls cleanly (not as much fun as the 454 in my last rig) to 5500 and keeps on working in the next gear. Power is as good as can be expected and mpg.s are around 17 tank to tank so I don't think I've got any other immediate engine problems to work through.
 
Good to hear. I don't know of any 5vz that will pull like a 454.

Found a new OEM TPS for $20 on CL. May replace mine as PM of sorts.
 
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