I am having some problems with my 91 6spd, and though I think I know the answer, I am afraid of what it might be...

Last summer, I replaced the injectors with some Bosch IIIs from our buddy at FIC. This was after a few months of head scratching, troubleshooting, and part swapping. Car ran pretty good, though I don't think it has ever been *exactly* right, meaning throttle response just doesn't feel the same, and power doesn't seem to be as linear with rpm (more sluggish in rpms < 2000). For example, it seems to my SOTP meter that it is struggling up slow hills in 6th gear where it didn't before.

My big problem is that about 3-4 months ago, I started getting a "hiccup" occasionally (maybe 1 or 2 times in a 15 min trip). No real rhyme or reason, but it just hiccups. It feels exactly like it did when my old injectors were going out. Being at a loss for ideas, I cleaned the IAC (which needed it) and tweaked the TPS. Everything ran fine for a while, but about a week or 2 ago, the hiccups returned. Most of the time it is at cracked throttle as I am cruising at constant speed, but last Friday it hiccupped during some spirited acceleration at about 3k-3.5k rpm.

I am afraid I have an injector problem again. All of the injectors ohm out ok (though curiously, the all on the driver's side check at 16.2 ohms hot, while the passenger sides check at 16.7-16.9 -- maybe some temperature issue?). Having been stranded several times by it last year, I am afraid to drive the thing anywhere long distance or take a passenger anywhere. Somebody tell me its not injectors again!

SB91

 

I don't think so as the coils are in spec but don't really come in to play with Bosch. Are you holding fuel pressure? Can you get a gauge and tape it to the windshield and see if when it acts up if you are loosing fuel pressure. How are your sensors? map, cts, TPS, o2's any recent scans? Look to see if the egr is sticking? How are your plug wires? any arking in the dark? When it has this hikup is it like the key went off suddenly or is it like starving?
Let me know
Jon Jr.

 

Thanks for the response...

Plugs and wires are new, but I haven't looked for any arcing.

I replaced the CTS about 2 years ago, the cold resistance checked out fine as recently as late last year, though I haven't checked it hot recently.

MAP is original, I have not done any diagnosis on it.

I actually swapped out the TPS this evening, no change.

o2 sensor is currently an ACDelco, I had put it in several months ago in place of a fairly new Bosch to try to address the sluggishness. Seemed to help a little. I didn't have any hiccups with the Bosch, so perhaps this could be an issue.

egr was inoperative early last year; I replaced with a new one. I believe it is working; it threw a code a while back when I accidentally left its vaccum line off after working on the t-stat. Fixed it, no code.

I have no scan data, but I guess I will be working toward getting set up to get some. I have done the pressure gage thing before when I was having the original issues and everything looked ok.

The reason I suspected injectors is because of how abrupt the hiccup is. It has complete power right before and right after; there is no sign that it is about to happen. It just totally cuts out for about 1/4 second and then resumes running, which is how my original injector problem would do. The only difference is that this just hits one time here and there where the original would happen constantly.

 

if you want to eliminate injector problem, I am willing to send you another set, but before you put them in make sure the tank is clean and you change the fuel filter. Dirt and sediment can clog an injector at any time. However the problem seems to be intermittent. You can change the injectors without pulling the plenum.. Did you know that? Thats one good feature of the bosch 3, so before you spend any money throwing parts at it, get the scan and lets make sure its all cool. Then call me and i will send you a set.
Jon Jr.

 

If you can, run a datalog that will probably shed some light on the problem. The 'hick cup" sounds like it could be a lean miss.

 

That does not sound like an injector problem. If one or more failed for a 1/4 second, I doubt you would lknow it, and it wouldn't be abrubt.
Datalogging is surely needed.

 

OK, (thanks to rodj and ch@0s in the other thread), I finally got my aldl setup working and got some info for both idle and 1900ish rpm, both at a stop. Unfortunately, my skills with Tunerpro are lacking to say the least. I can't figure out how to get it to export aldl values/flags to plain text, so here it is as images!

This was just after a drive home from work, mixed driving for about 15 mins. Shut the car off to run inside and get the laptop, plugged up, connected, fired up, logged. Also of note is that I have a hypertech prom from the PO, not sure if that means anything.

Idle:
1900 rpm:
First thing I noticed was the BLM was 149. I believe this should be 128, correct? I notice during the playback that the Rich/Lean flag is flopping back and forth pretty quickly, which I understand to be proper operation.

Also, I noticed when I started pressing the throttle with the pc connected that I got a SYS flash, then returned to normal. I also got a brief SYS the next time I tried to fire up, (then returned to normal). Is this normal when reading the aldl interface?

Also not sure about the "Malfunction Word 1", are these historical codes? The "No Reference Pulses" got me thinking... one other quirk of the car is that it doesn't like to start on the first turn; I usually have to crank it, stop, and hit the starter again. On the 2nd go, it fires up immediately. This happens even if I let the fuel pump cycle before starting. I had been thinking maybe this is a fuel pressure thing, but maybe the ecm isn't seeing ignition signal right off? Dunno, just speculating

Thanks for your help guys,
SB91