EDIT 6/19/12: To keep from spamming new threads, I'm posting changes as I go in this one. If you don't want to read the whole story, please just scroll to the last post to see what's currently going on. Thanks in advance for any help and/or advice anyone can provide.

Okay, where to start... I am a somewhat accomplished shadetree mechanic, but I've never had much luck with pre-OBDII fuel injection. Right now I am frustrated to my wit's end and need to ask for a little input from anyone who cares to chime in. This is going to be a bit of a long post, so make sure your drink of choice is topped off and get comfortable.

I bought this car back in December 2011, a 1992 T-Top RS that I had my eye on for months. I got a screaming deal on it but I knew it came with some issues. It idled very high (about 1200 RPM when warmed up, closer to 2500 when cold). It always ran super rich, and I tried changing the CTS with no change. After about three weeks, it started randomly stalling out in traffic and then the fuel pump went out altogether. I put in a new TPI pump (cheapo chinese unit), sock, and filter and that lasted almost a week running even richer than it had in the beginning before once again I was getting no fuel pressure. Assuming it was just a bad fuel pump, I swapped it out under warranty and it still ran super rich (I'm talking black smoke out the tailpipes kind of rich) only this time it made it only about half a mile down the road from my house before this second fuel pump died.

After that the car sat for a few months until last weekend. I did some thinking and disconnected the return fuel line under the hood and tried blowing into it with no luck. Basically there was a blockage stopping fuel from returning to the tank, causing the pumps to burn up. So I bought a new Bosch TBI fuel pump and also got a rebuild kit for the TBI. When I pulled the TBI, I noticed there was a vacuum port on the backside of it not plugged into anything, so I bought a cap for that and hoped that may take care of my high idle. When I got into the fuel tank, I noticed a large piece of metal that appeared to be some sort of brace that had come loose inside the tank. It looked like this may be causing some problems, so I spent the next 5 hours with tin snips and channel locks slowly chopping this brace up and pulling it out through the fuel pump hole. Yes, I know I should have just bought a new tank, but I have way more time than I do money. After all was said and done, I dropped in the new pump and closed everything back up, and tried the blow test again at the return line under the hood. This time it felt like there was no restriction, so I reconnected it and tried to fire her up for the first time in a few months.

I had to jump it off, and it just would not catch, so I poured a little gas down in the throttle body since I had drained all the fuel out of the lines and it fired up. It still ran rich, and the idle was bouncing between about 600-1100 RPM and this time the CEL was on (it never came on before). I let it run up to temperature and decided to come back the next day to fool with it more and start troubleshooting again. The next day after work, I went out and tried to crank it but again it just would not even try to catch until I poured a little gas into the throttle body. Again, the idle was all over the place and so I decided to try to reset the IAC like I had read about in some of my googling.

Here is where I got really stupid. I remembered reading about jumping pins A&B on the ALDL then turning the key on to reset the IAC. Now stupid ol' me assumed that A and B would be the first two pins on the lefthand side of the top row of the ALDL, which I now believe are actually pins E and F. So I jumped those two top left pins with a paper clip and turned the key to 'on' for about 30 seconds. I was wondering why the CEL didnt flash any codes, but then I turned the key off, removed the paper clip, and again tried to start the engine. Once again, it spun without the slightest hint of trying to catch so I again poured some gas down into the TBI. This time, once it cranked it would not even attempt to idle. I had to keep my foot on the gas pedal to keep it running and anytime I let it drop below about 2000 RPM, the engine died and I would again have to pour more gas into the TBI to get it restarted. To top it all off, the wiring for my rigged up manual cooling fan switch melted so I had to call it a day (I live in GA where right now we are already low 90's temps so without a cooling fan overheating happens very quickly when having to keep the engine running at 2K RPM or above while sitting still).

My question mainly is where do I even start? Specifically, I'd like to know:
1) What, if any, potential damage did I do by jumping pins E and F on the ALDL then turning the key on? Did I fry the computer?
2) How can I test the IAC? I don't want to start just throwing parts at this car without having some idea that what I'm buying will do any good or not. My previous experience with fuel injection would lead me to believe that at least one of my problems is a bad IAC, although I have seen faulty/clogged EGR cause the same type of idle fluctuations.
3) Is there anything else I should check? I plan on trying to pull codes the next chance I get to mess with the car, either this evening or tomorrow after work

When I rebuilt the TBI I was very careful to clean all gasket surfaces and once I got it cranked up I checked for any vacuum leaks by spraying carb cleaner all around the gaskets and vacuum lines, because vacuum leaks can be a nightmare. Any hints, ideas, or suggestions you guys (or gals) might have would be greatly appreciated. I'm really about ready to call the scrap yard to come get this thing before I have to up my blood pressure meds. Thanks in advance for any input and I will post any codes I can get as soon as I can pull them.

 

Get a fuel pressure test gauge & test it. Stock spec is 9-13psi.
Make sure the ign. timing is correct & advances when you rev it.
Make sure the map sensor is hooked to the right port.
Carefully check the ecm grounds, some are at the back of the heads or at the t stat housing. You can test them at the ecm connector w/ a dvom, set on ohms.

 

the port on the back of the tbi if it is a long tube is suppose to go to the map sensor. it wont idle corrctly without it.

 

Thanks for your reply, ex-x-fire, where is the best place to connect a fuel pressure gauge? I have seen some suggest placing a tee down by the fuel filter but it seems to me somewhere under the hood up near the throttle body might be more accurate and easy to read. I will also check the map sensor, as the vacuum port that one92rs indicated is supposed to go to it was not connected to anything and I now have it capped off. Where is the ECM located at on these cars? Is it in the passenger side kick panel or somewhere in the dash? I'll do the ohm test like you suggested, but do you know an acceptable range of ohms? Thanks again to both responders!

 

ECM is passenger side under dash. Pull the cover off. Two lil screws drop the ecm bracket and ecm out.

 

UPDATE: Okay, I found a good deal on an Actron TBI fuel pressure gauge on ebay and ordered it, should be here sometime this week. The MAP sensor was connected to one of the smaller ports on the front of the TBI, so I moved it to the long port on the back which was previously capped, and found a loose vacuum line from the EGR system that fit right on the small port I took the MAP line off of, so now all vacuum ports are connected (hopefully correctly). I checked the ecm ground and it is good, and then I ran codes: I got 12, 23, and 54. A quick google search revealed 12 is a standard code the ecm throws when codes are pulled, 23 is for intake air temp sensor (which made sense since I had the air cleaner off and the sensor unplugged). Code 54 was fuel pump relay related, so I swapped the relay with the one next to it, since they appeared identical. Once I removed the jumper and tried to crank it, I could hear the fuel pump priming which I didn't hear before, which I'm sure is why I always had to pour a little gas into the throttle body to get it to crank. It cranked up but still did not want to idle. I found a how-to on resetting the IAC, so I did that and now it idles, but still rough. It doesn't seem to be loading up nearly as bad, but there is still something going on here. I was going to check timing next but we got hit by a monsoon storm that is going to last until mid week, so hopefully my fuel pressure gauge will be in by then. Any ideas on other things to check? It almost sounds (and smells) to me like the EGR may be sticking, but I'm not sure how to check it on these engines. I saw a thread on removing it altogether, is that worth the hassle? We don't have any kind of emissions testing here and I doubt we ever will before this car hits the 25 year rolling exemption window, so keeping it smog legal is of little concern to me. I did rerun codes after the ecm relearned the idle and found nothing. Thanks again to all those who have provided advice!

 

Ive run a tpi fuel pump in a TBI car for a few years and it was regulated to 13psi and was never a problem.

 

@Jeffs82TA, that's why I bought the TPI fuel pump in the first place, but the problem was the higher volume only exacerbated the blockage in the return line. Right now I am so sick of dealing with that gas tank I am not going back in there anytime soon if I can help it.

 

UPDATE: Some problems solved, and now for some new ones. I didn;t want to spam up the boar with a new thread so here goes. If you just want to see my new questions, please scroll down.

Okay, my FP Gauge came in and I got the chance to work on the RS Saturday. the instructions said to connect it on the tank side of the filter, but I chose to install it on the engine side, as I figured that would give a more accurate view of the actual FP reaching the engine in the case that my almost new filter was clogged. Imagine my surprise when I cranked it up and the gauge shot up to 35 PSI! It would dip down when I goosed the throttle but then shoot right back up. I knew the FPR was good because I just rebuilt the whole TBI and installed a new diaphragm, so the first thing I did was disconnect the return line under the hood and ran a chunk of hose into a 5 gal can. This time when I cranked it up the gauge stayed at 10.5 PSI, right where it should be in the 9-13 PSI range. I worked my way back to the rubber lines by the back axle and disconnected the return line there and again ran it to a gas can and once again had 10.5 PSI. At this point, I knew the restriction was somewhere between there and the tank, so out came the fuel sending unit for the 4th time in the past few months. It took me a while to figure it out, but at some point someone had swapped the two 5/16" connections, so the return line was connected where the vent line for the charcoal canister should go and vice versa.The little check ball meant to stop fuel from pouring out in a rollover was restricting the return flow and causing elevated pressure, which I'm sure killed the two TPI (higher flowing) pumps that I had previously installed.

Everything buttoned back up, cranked it up, checked for leaks and got 10.5 PSI still, so I pulled the FP Gauge T-Fitting and went for a test drive. I noticed a lot of weird flat spots but that seemed to get better as I drove. It also stalled in gear at stop lights at first but that also seemed to improve. I still plan to check the plugs, as I'm sure running that rich for that long fouled them something good, which could lead to some of the rough running.

NEW EVENTS: On my way to work this morning, it took a long time cranking over to catch up, and on the way I noticed the speedo was not working. It seemed to run good with no flat spots and didn't even try to stall at red lights, then it stalled pulling into the parking lot and wouldn't easily crank back up. (I was already late and I coasted into a customer parking spot and just left it for the time being. I just went out on my lunch break and pulled codes, I got another 54 which I had before and knew it meant FP Relay. I had gotten this before and swapped the fuel pump and fan relays already so I figured maybe they were both bad (maybe the FP running at that high PSI had pulled too much amps and burned them both out?) I pulled the relay and jumpered the orange and grey wires and was relieved to hear the pump priming, so I turned the key and it cranked right up. Thinking I had found the issue, I tested the relay by applying 12v to the two smaller terminals (I think D&F?) and heard the click of the relay closing. Stumped, I reinstalled it and tried cranking, the FP primed and it cranked right up.

QUESTIONS: Should I start by trying a new FP relay? They are about $13 at the parts store. I hate throwing parts at a car but for that price it's a cheap rule out. Could the PASSlock system be coming into play here? I seem to remember thinking it had a FP cutoff, but I could be way off base. If a new relay still only occasionally primes the pump, should I start looking at the ECM? Reman ones are about $75 locally, not bad but more than I want to spend at this point unless I know 100% that will fix things. As far as the speedo, where do I start diagnosis? I did a search and found some threads with VSS output specs, I think I will try that. There were no codes about it and the needle does twitch a little when the key is turned from 'off' to 'on', so I'm worried this might be another sign of the ECM going south. Finally, I wanted to check the timing. I read up and found that, like most EFI vehicles, there is a wire to the computer (ETC?) that needs to be disconnected. I found several references to the color of the wire but not where it is located? Anyone who can point me in the right direction, it would be greatly appreciated. Sorry for the long post but thanks in advance for any help and/or input.

 

The thing you cut out of the tank is a baffle and will affect drivabilty on any moderate cornering or bumpy road when under half a tank. Pump will cavitate and cause loss of power or just general rough running. You should not disconnect the return line and then measure fuel pressure. There is something wrong with either your FPR or return line or fuel pump or any combination. Idealy you want ti see 13 psi. Not 12 or 11 or 10.5. 13. You can make your stock FPR (somewhat) adjustable. Try searching on google/tgo. It also sounds like the throttle shafts are worn on your TBI causing high idle. I recommend to anybody with OBDI to get an ALDL cable and a cheap lap top, unless you like smashing your head agaist a wall.

 

Thank you, I had a feeling it was some sort of baffle. It was flopping around loose in the tank, and my rationale was that it wasn't able to serve it's intended purpose, and it would probably do more harm than good flopping around like that. I know I should have replaced the tank, but at that time I didn't want to spend the money until I got the car running right. The only reason I disconnected the return line was to find out where exactly the blockage was that was causing my FP to spike up to 35 PSI. I did it as safely as I could and I only ran the engine a few seconds each time until I found the problem. About adjusting the stock FPR, I read about that and thought of drilling it out when I had it apart cleaning and rebuilding it. I still might do it, but at this point I have bigger issues with that car and I'm hoping that 10.5 PSI is good enough to get it running decent before I start doing any mods. About the ALDL cable, I've been looking into making one or buying a cheapo one, is there anything in particular you'd recommend? I'd like to keep it around $20, if possible. Ideally, I'd prefer to buy just the ALDL plug end and I can provide the serial connector and patch cable.

NEW EVENTS 6/19/12: Okay, after work yesterday I cranked it with a paper clip and drove it to the parts store. The speedo was working fine, so I'm thinking it was a fluke or maybe an intermittent bad groud somewhere. I tried putting in a new FP relay, but it is still not priming the fuel pump prior to cranking. Additionally, the oil pressure gauge is dipping low at idle, causing the FP to cut off and stall the engine. Eventually after two or three times of stalling in rush hour traffic and having to jump out and hotwire the FP relay to restart it, I just left the paper clip in there for the rest of the drive home. This weekend, I'm planning on troubleshooting the low oil pressure as well as the FP priming circuit, but I do have a few questions:

1) Is the Oil Pressure Sending unit that sends the signal to the gauge cluster in the dash the same one that controls the fuel pump?

2) What Oil PSI is the low threshold for cutting off juice to the fuel pump? 10? 5?

3) Any advice on troubleshooting the priming circuit? It seems to work every once in a while on it's own, but mostly I have to jumper the orange and grey wires at the relay to get it going. Ideally, I'd like a wiring diagram if possible, but I know that's asking a lot. I'm going to pull the ECM back out this weekend and check all the terminals for corrosion and make also recheck the grounds.

Thank you in advance once again to anyone who can provide any sort of help/advice/sympathy/etc.

 

1). Yes, it should be a three terminal switch which runs both the dash and the fuel pump back up.

2). closes above 4 psi

3). since it is working intermittently it may be that the socket for the relay is bad. Look for corrosion in/on the terminals along with burned or frayed wires.

Wiring diagram attached.

RBob.

 

Thank you, RBob!

I took a good long hard look at the diagram and thought of spending hours out in the GA heat unwrapping and chasing wires. Then I thought what if it turns out to look like bad ECM? Thats about $80, with no guarantee of a fix. Eventually, I just decided to cut the wire at the FP relay that goes to the ECM and spliced it into a 12V+ IGN power source. Most other fuel injected cars I have worked on run the fuel pump the whole time the ignition is switched on, just because GM decided to overly complicate their system doesn't mean I should have to deal with it...

While I was under there, I trashed the crappy cooling fan wiring setup that was installed by a PO. The cooling fan was previously run with a little toggle switch getting current directly from a wire spliced into the back of the cigarette lighter and then a tiny 16ga wire run all the way up and plugged directly into the fan motor with a little terminal connector. Unfortunately, I could not readily locate a factory style pigtail connector, but I did locate the cut off factory wires and spliced in 10ga wire with insulated terminals. Then I ran BAT 12V+ from the fuse box up to a nice toggle switch mounted on the dash and then up to the factory relay. In a Homer Simpson 'DOH!' moment, I was scratching my head trying to figure out why it wouldn't work when I remembered thinking I heard somewhere that the factory setup relies on the sending unit to provide ground to the relay, so I spliced in a ground wire to the firewall and all was well. Eventually, I might work on diagnosing the factory circuit or just go with an aftermarket adjustable temperature fan switch but for now it's all good.

I took it out for a road test and it did better than it ever has since I have owned it. Still has a few issues to work out, and I'm really thinking of selling it to buy an older carbed model. Thanks once again for all the help, and I hope sharing my experiences might help someone else reading this on down the line.