I need help! My 87 t-type bucks when i go past half throttle. It drives fine around town but when you get past half pedal it builds boost to 18-19 lbs then it falls on its face rpm's drop and boost drops to ten lbs. It will keep doing this all the way past 100 mph until I let off the pedal below half throttle. I've changed the plugs,fuel filter, fuel pump (red armstrong&hotwire kit)plug wires. Could it possibly be the coil pack since it only does it under a load or the valve springs since i'm not seeing higher rpm's? Also, I have installed a TE 44 turbo and the car came with green stripe injectors.
Green stripes are definitely marginal for that much turbo. Sounds like maybe you have a combination of not enough fuel and too much boost for the octane.
It does the same thing with c16 race fuel in it. I have been told that the 009 injectors would be a good replacement for those injectors. The funny thing about it is I ran it on a Sunday at the track and ran a 12.47 took it to the track Wednesday that same week and it started that problem on its first pass and ran a 13.5 and the second pass was a 13.9.
sound like a fuel or ignition problem, check the TPS setting at idle and WOT. If you did 12.4 with
the same setup you should do again
Had exactly the same problem when my car was nearly new. It was the coil pack. Once replaced (under warranty), it ran fine.
When was the last time the fuel filter was changed? Have you checked to see if your fuel pressure is constant during this?
Also, as far as the runs go, true it shouldn't vary that much, but if your weather there is anything like here, St.Louis, Mo, I can see the weather being a BIG factor even from day to day. Yesterday it was a heat index of like 105-110, today it was in the high 80s. Big difference in track times if the weather bounces around like that.
Do you have any kind of scantool? I would try to get a reading on the fuel pressure during a run and see if it's doing anything, then it should be narrowed down to either fuel or spark.
Check TPS "smoothness" as you push the gas pedal (engine off, key on, of course) from idle to WOT. Also like Nick suggested, Fuel pressure while running...can't be without a scan tool.
I really appreciate the help guys. Here's what tried last night. I turned up the fuel pressure to 55 lbs to see if I was getting enough fuel and that did not solve the problem. I then tried tuning the boost down, I put it at 16 psi and it solved some of the problem but I still have the bucking problem when I put it to the floor now. I still can't understand it. I did all this with c16 race fuel so I know its not an octane problem. Also, I ran at the track with 21 to 22 psi of boost with no problem before and thats when I made all my mid 12 passes. Please help guys! The 1991 Z28 I traded for this car is running mid 11's now. I cant let my friend beat me in a car that was mine.
Ok here's what i tried last nite for the second nite. I checked my coil pack with an ohm meter and from pole to pole I got 11 ohms on each coil which I was told to be good. Next I checked my tps I get .42 volts closed throttle and I get 4.82 volts at WOT which I was told to be correct also. I also changed my O2 sensor with a new one from GM to no avail still have the problem. My next step is to make a pass on the street with it with a fuel gauge on it to see what the fuel pressure is doing at WOT.
Did you check for clean, tight grounds on the back of the pass. cyl. head?
That will be added to the list tonight to check for. I think my fuel pressure regulator might be acting up.thanks Donald
Using an ohm meter isn't really the best way to check your coil/module. I know that 11k-13k is supposed to be OK, but it's no guarantee. Mine tested fine, all around 12.5k but when I hooked up a coil tester, I found that one of the towers had a miss at increased rpm. How high it was I have no idea, but it didn't take too much of a turn of the knob to see it mis-firing. With the knob turned all the way, the other two were a bright spark, the other was dead. I changed the coil pack, tested it and it was fine all the way up. I then noticed the car seemed to rev better and it didn't have an intermittent miss anymore. Check the fp and the grounds and let us know what happens. Just keep what I said in mind, that the ohm test isn't exact. Good luck.
ok guys here's what i've tried. I checked my grounds and they're tight. I checked my fuel pressure at WOT and it stays up all the while im running the car. I changed my valve springs just for the heck of it and my problem still exists. I've tried to get to a place to test my coil pack but I can't seem to find a place that does so. I think I've narrowed my problem down to my coil pack,ignition module, or PCM. Any help on these three pieces causing my problem guys?
ok here's a new one. Last night I changed my coil pack on my car hoping that would cure my car of the problem. Well it took a step backwards, now my car won't start. My last resort is my ignition module. It's the last part I didn't change and I don't have any spark coming from the coil. Man,I never knew these cars could cause problems like this!
Any updates yet? My car seems to be doing the same thing, except I get a pop (backfire) from the intake. I was able to ease into the throttle and reached 15lbs of boost but as soon as I went past 1/2 throttle, I got the pop again. It seems to me like the timing is to far advanced (like on an engine with a distributor). Would moving the cam position sensor have any affect on this?
Problem solved....it was the coilpack.
well guys im back again and my car is still running like crap but worse. Now as soon as i put it in drive and barely touch the gas it acts like its misfiring. it has a new coil pack, ignition module, new pcm, new o2 sensor and i still have no idea what it is. do you think it could be a knock sensor messing up the timing or maybe a head gasket blew from running too much boost on pump gas , or could it be a burnt valve?
I had the same problem/symptons last year. Thought I had a bad injector or ignition part. Did a lot of probing and diagnostics. Finally replaced the mass air flow sensor and everything ran okay for 5 minutes than back to the mis-fire. Double check everything again, spent 8 days doing this, came back with same solution. Replaced the MAF with a different brand this time and everythings been running great since.
Hello Bobbyd,
MAF sensor is a good idea. Try just unprugging it first. see how it idles and easy driving. If this is your fix, great. If not, take a close look at the wires coming out of the ignition module. Pay attention to the Pink/Black wires. We had a situation here were the customer complained of a gradual lose of power and our test drive (heavy throttle) caused big backfires. Result - his wires (in the green weatherpack insulation were oxydized and needed to be repaired. With throttle the engine torques and caused the break of signal. We checked all the wires and found 2 or three bad ones. This was his solution.
Hope this helps,
John @ ESP
hey guys i found the problem. It was my MAF. I got one from a parts store replaced it and it ran like a dream. I took it to the track and did a 12.53 at 109. I appreciate all the help guys. I also ended up with alot of spare parts but they work good for test parts in the future. I plan on getting the MAF translator and 3 inch LT1 MAF. I finally got my car back!