Hi all, long time reader and first time poster!

I've been the proud owner of a 1992 Camaro RS 305 TBI with a T5 over in the UK for over 20 years. In that time, it's been very rare to have any issues (it's only done 41k miles) & especially ones that aren't pretty straightforward to resolve. However, over the last 6 months, it's been having issues with its running that are getting to me. When it starts there are no issues, however, as the revs start to drop (like it's coming off choke), the revs drop drastically and it seems like it's going to stall. Then there's a blip of power, as I guess the computer detects this and it recovers. Then it drops off again and the same thing happens. This continues to happen until it's warmed up, where it idles normally. If I then drive it down the road, the power isn't smooth and it jumps about under acceleration being very lacklustre in power.

I made a video of how it runs today & posted it to YouTube, so hopefully this link works: https://youtu.be/Rh2ymHYWYT8

I've done some reading on these boards and found lots of interesting things, but I don't seem to be any closer to resolving the issue. I have also take it to a local garage and tried some of the things they suggest also with no affect. Below are the things I've tried so far & I'd really appreciate any additional thoughts. Thanks so much.

Replaced the Fuel Filter
Ran a full fuel tank with some Redex fuel cleaner
Replaced the Coolant temp sensor
Replaced the IAC
The garage ran a vacuum check and found no leaks
I also disconnected the battery after each change to make sure it had a fresh map, but the issue remains.

Thanks again if you got this far & for any suggestions
James

 

A nice photo of it, so you can see why I want to get it working properly again!

 

Have you verified fuel pressure? These pumps are know for slowly dying vs immediate failure.

 

Not yet. I don’t have the tools for that one. I had hoped to find a set with the TBI adapter in it, but can’t seem to find a reasonably priced one in the UK. Would it be something a garage can do pretty easily? Or do I have a different option?

 

might ask if the line fittings in the kit are gm saginaw, can put inplace of the fuel filter.

 

How easy is it to read the pressure with a gauge that goes that high?

 

Ask the seller for a gauge picture. I’m sure it has 2 psi increments .

 

they replied back & youre correct. 2 psi increments. Kit ordered and I’ll give it a go when it shows up. Thanks for the suggestions & will keep you posted!

 

When you replaced the IAC did you clean the port inside the TBI? Assuming you did an IAC reset when replacing it?

I've heard that should fuel supply be an issue (9 psi to 13 psi required) you may want to investigate further the externally mounted fuel tank pressure relief valve mounted over top of the rear axle (drivers side or LH ). Over time it can get stuck, especially with the road/gravel conditions of the UK, trust me - I know with past MOT's. Unable to relieve pressure it puts a strain on the fuel pump when trying to perform in a deep vacuum. Its pretty easy to remove, disassemble, clean and reinstall but they are selling them online.

Another thing to throw at it with remote troubleshooting is a PCV.

I'm also hoping you went AC Delco on the parts...

I recently downloaded TunerPro RT and with an ALDL cable have datalogged. It is a great friend in the world of troubleshooting things like this.

All the best and good luck.

Cheers,

-CB

 

@bennettcvcu is right on it. Be sure the throttle body is clean, the shaft is tight and not worn, and the blade(s) are in position and fully closing. Then verify the TPS is sensing correctly and within specs, and adjust the throttle stop minimum air position to specs. If you are going to be in there, it would be good to verify the injector pod is not leaking. Once that is resolved and the fuel pressure is verified, other items can be considered.

Another item which can affect the idle is the PCV valve. An incorrect valve can create problems, which is why I generally try to clean the original valve and re-use it. The PCV valve has two calibrated springs, and a pintle tip and body designed specifically for an engine family. They are NOT universal, despite what your parts store replacement interchange might indicate.

The video clip appears to demonstrate the stall saver programming in action, most probably due to an incorrect IAC action and/or minimum air setting. If you have the original IAC, it can be cleaned, lubricated, its spring re-tensioned, and returned to service is there is any question about the replacement part being suitable.

One thing to bear in mind - When the battery is disconnected the ECM reverts to its default stock/backup mode. It can take several drive cycles at multiple tens of kilometers to allow the ECM/blm/int to rebuild the data tables that work with your specific vehicle. This has always seemed to be more prevalent on speed-density vehicles versus fully sensored types.

 

Hey CB,

Thanks so much for the reply & sorry for not posting back until now. Time is a bit on the limited side when it comes to getting anything done on the car

Ok, so when I replaced the IAC, the port was completely clean, which is something that I've noticed as I've been working through the engine bay. Nearly all of the connectors seem to only be coming apart for the first time. The new IAC looked the same as the old one, so I just put it in It didn't make any difference, but I didn't do the reset. I even put the old one back in, but the problem was identical. I'll try resetting the IAC next time I work on the car. I'm still waiting for the Fuel Pressure Testing kit to arrive (expected this week) so I can give that a go. Will also try and take a look at the pressure relief valve as suggested.

Thanks!

 

Hi all,
Ok, I managed to get some time with the fuel pressure testing. However, the rubber used in the kit seems to react with the fuel and swells up, which then means the gauge doesn't read the pressure properly. I ended up using a gauge from a separate pump which also showed a better range. The pressure only seems to get as high as 4.5 PSI. I also tried it with clamping the return, disconnecting the injectors and applying 12V to the fuel pump, but the reading was the same. No leaks from anywhere that I can see.


This is as good as it got for pressure!

 

There's your sign. Time for a pump.

 

That was the first thing that the Haynes manual suggested we look at. If I removed the old one and then put it back in again, would the idle still need adjusting? As I mentioned previously, I did pick up a new one, but there was no difference at all, so I wasn't sure that the IAC was the cause. Once the car is warm, it idles fine, but doesn't pull smoothly when driving. Would the IAC also cause that?

Thanks so much guys.
James

 

That's kind of where I was at
Might I ask, it's a 92 RS, so which pump is suggested?
Also, will changing the pump definitely fix the idle problem? Or is it likely that there are multiple issues?

Thanks

 

No one from "here" (this side of the computer screen) can say decisively if there are other problems or not. We CAN say decisively, that your fuel delivery is definitely an objective problem (which could and likely would affect idle -and the other symptoms that you described), so you should just go ahead and fix that....the assess.

Any off the shelf pump for that application is fine. If you're planning big, future mods, you may want to get a pump for a MPFI version of the same car (a pump for that car that came with TPI) which will give you a large surplus of pump capacity.

 

There's no way to answer that here. As with all troubleshooting, fix the obvious stuff first (in your case, low fuel pressure), and then see where you're at.

As far as which pump to buy, for myself, I usually decline to specify a brand due to the unfortunately sketchy quality of so many formerly good-quality repair parts brands that are now considered to be junk. Others here will likely step in with their own suggestions though.

 

Any TPI replacement pump would work, along with the trusty Walbro 255. Buy from a reputable source as there are some fake Walbro's out there.

 

No, I realise that and I thought it as I was typing it too. Totally fair & I thank you all for your suggestions.

The car is pretty much stock & I always said I'd keep it so, as far as was possible anyway. If it's much more expensive to keep stock over an upgrade item, I'd probably go with the upgrade, but I wasn't planning on doing anything major. Certainly nothing that would require significant additional fuel flow at this time.

It's going to take me quite some time to get the time to do the pump, but I have some garage space. I was planning on taking it all to bits and seeing what I need, then purchasing it all in one lot before reinstalling. As the rear end is down, I'd also like to take some time rubbing down and sorting the rusty bits. You know, the stuff that won't get looked at again