Slow! 93' Mtx

[SHOracer14]

Ok, I am officially stumped on this car. By far the slowest SHO I have owned... it just doesn't seem to have the pull my other cars had. Everything has been done on this car (it has a well documented history @ 163k, full 60k done about 2 years ago) so figured some basic cleaning and maintenance was in order. I pulled the intake and cleaned it inside and out, new plugs and new fuel filter with injector cleaner. I also ran the codes and the only two that popped up were primary and secondary fuel pump circuit failures so those must have been stored. Also, the car has a walbro 155 and some sort of factory spec remanned MAF on it. I put everything back together and there was no change. I got to thinking about it and it seriously feels like the SpOUT circuit is open but it does not throw the code and the connections are good. I figured maybe something else is causing the PCM to retard the ignition. I don't have access to a timing light until tomorrow but, what should the car be running at idle?? I threw it on the scanner at work and the computer told me to check the SpOUT connections and make sure the car is running at 20 degrees. Is that correct timing at idle? My other question is this. I always thought the SpOUT jumpers were just a jumper that only closed the circuit when installed. Are they actually a resistor and possible be bad? Maybe not bad enough to throw a CE but bad enough to have timing slightly reduced? I have no clue, the car starts, runs and idles smooth as heck... it just doesn't seem to have the power. My next step after checking the timing is a compression test and changing that MAF to a factory unit. My only other thought is possibly a clogged cat. Any other ideas? All help is appreciated.
EDIT- Put a factory MAF in the car with no change.

 

[SHOtime2511]

i have heard that the throttle cable can stretch,thus causing the TB to never open fully under WOT.....its worth a shot

 

[Denny]

Timing belt might be off by a single tooth as well

 

[revhardSHO]

Make sure you are getting good fuel pressure from that pump, check the MAF and maybe try another TPS.

 

[SHOracer14]

i have heard that the throttle cable can stretch,thus causing the TB to never open fully under WOT.....its worth a shot

I already checked that in fact it was the first thing I thought of... definately seen it before though.

Timing belt might be off by a single tooth as well

Possible but it runs so smooth I doubt it... I may end up pulling the cover if all else fails.

Make sure you are getting good fuel pressure from that pump, check the MAF and maybe try another TPS.

I should check that fuel pressure and you did remind me that I want to check that TPS voltage... I also have a spare I will try. MAF is definately good... pulled from one of my previous strong running cars.

Thanks for the ideas guys keep em' coming!

 

[LeddZepp8687]

Maybe its just a factory slouch?

 

[SHOtime2511]

id check the fuel presure,and the timing as well before anything else.
these seem to be the top reasons when an otherwise well maintained
SHO is unexpectedly slow

 

[projectSHO89]

With the SPOUT plug pulled, base timing should default to 10 DBTDC.

With the SPOUT plug installed, timing should advance significantly, up to 20 degrees or more of additional advance depending on engine speed and other variables.

The instructions for the advance are generated in the PCM, but are processed and executed by the microcontroller in the DIS module. The SPOUT plug is the link between the systems that carries the signal to the DIS module. The DIS module provides feedback to the PCM via the Ignition Diagnostic Monitor (IDM) signal. IDM, which is also used for the TACH, is a composite of the PIP, CMP, and COILS 1,2,&3.

When you have that light. check base timing , then check for proper advance.

MAF can be checked by just unplugging it. If it's faulty, the PCM's defaults will cause the engine to run better. Do the same for the MAP/BARO sensor. If it's detecting the wrong altitude, the engine will run like a dog.
Ignore the CEL during these tests, but reset the PCM afterwards.

Measure for correct fuel pressure: 39-45 psi at idle (FPR vacuum line off and plugged), around 30-32 psi with FPR connected. Also check under load.

Verify proper secondaries operation - Close at startup, open at 4K.

I'd also pull the top timing cover and check the belt for slack and check to make certain the cams are properly timed. Set the crank at 0 TDC, the index dots on the cam gears will either be dead on 6 or 12 oclock. If they happen to be at 6 oclock, give the crank another revolution to put the indexs at 12 oclock. Make certain the dots line up exactly with the marks on the inner timing cover.

Pull dampener and inspect for "crank cancer". You really don't want to find this. If you pull that upper timing cover and find a fine reddish powder coating, be prepared for this. When present, the engine usually (but not always) presents a knocking sound but you didn't mention one.

Steve

 

[SASHO91]

With the SPOUT plug pulled, base timing should default to 10 DBTDC.

With the SPOUT plug installed, timing should advance significantly, up to 20 degrees or more of additional advance depending on engine speed and other variables.

The instructions for the advance are generated in the PCM, but are processed and executed by the microcontroller in the DIS module. The SPOUT plug is the link between the systems that carries the signal to the DIS module. The DIS module provides feedback to the PCM via the Ignition Diagnostic Monitor (IDM) signal. IDM, which is also used for the TACH, is a composite of the PIP, CMP, and COILS 1,2,&3.

When you have that light. check base timing , then check for proper advance.

MAF can be checked by just unplugging it. If it's faulty, the PCM's defaults will cause the engine to run better. Do the same for the MAP/BARO sensor. If it's detecting the wrong altitude, the engine will run like a dog.
Ignore the CEL during these tests, but reset the PCM afterwards.

Measure for correct fuel pressure: 39-45 psi at idle (FPR vacuum line off and plugged), around 30-32 psi with FPR connected. Also check under load.

Verify proper secondaries operation - Close at startup, open at 4K.

I'd also pull the top timing cover and check the belt for slack and check to make certain the cams are properly timed. Set the crank at 0 TDC, the index dots on the cam gears will either be dead on 6 or 12 oclock. If they happen to be at 6 oclock, give the crank another revolution to put the indexs at 12 oclock. Make certain the dots line up exactly with the marks on the inner timing cover.

Pull dampener and inspect for "crank cancer". You really don't want to find this. If you pull that upper timing cover and find a fine reddish powder coating, be prepared for this. When present, the engine usually (but not always) presents a knocking sound but you didn't mention one.

Steve

Awesome info steve!
Hmm.. i may go swap BARO/MAP sensors now... just for kicks...

What is the redish powder? Where is it from?

 

[projectSHO89]

What is the redish powder? Where is it from?

Rusty iron particles that were once part of the crankshaft....

 

[SASHO91]

oh... forgot about that..
looking at it agian i see it now.

 

[smak]

poor performance can also be caused by cylender walls that have been stained/scorched with oil deposits over the years leaving the piston rings a poor mating surface.

i did a 2 bottle auto-rx treatment and have noticed great gains in power and most of all fuel economy.

www.auto-rx.com (fixed link, my bad)

or maybe it just wasent broken in properly and the engine never seated the rings right in the first place (in which case a rehone is in order i believe)

 

[SHOracer14]

With the SPOUT plug pulled, base timing should default to 10 DBTDC.

With the SPOUT plug installed, timing should advance significantly, up to 20 degrees or more of additional advance depending on engine speed and other variables.

The instructions for the advance are generated in the PCM, but are processed and executed by the microcontroller in the DIS module. The SPOUT plug is the link between the systems that carries the signal to the DIS module. The DIS module provides feedback to the PCM via the Ignition Diagnostic Monitor (IDM) signal. IDM, which is also used for the TACH, is a composite of the PIP, CMP, and COILS 1,2,&3.

When you have that light. check base timing , then check for proper advance.

MAF can be checked by just unplugging it. If it's faulty, the PCM's defaults will cause the engine to run better. Do the same for the MAP/BARO sensor. If it's detecting the wrong altitude, the engine will run like a dog.
Ignore the CEL during these tests, but reset the PCM afterwards.

Measure for correct fuel pressure: 39-45 psi at idle (FPR vacuum line off and plugged), around 30-32 psi with FPR connected. Also check under load.

Verify proper secondaries operation - Close at startup, open at 4K.

I'd also pull the top timing cover and check the belt for slack and check to make certain the cams are properly timed. Set the crank at 0 TDC, the index dots on the cam gears will either be dead on 6 or 12 oclock. If they happen to be at 6 oclock, give the crank another revolution to put the indexs at 12 oclock. Make certain the dots line up exactly with the marks on the inner timing cover.

Pull dampener and inspect for "crank cancer". You really don't want to find this. If you pull that upper timing cover and find a fine reddish powder coating, be prepared for this. When present, the engine usually (but not always) presents a knocking sound but you didn't mention one.

Steve

Very awsome info sir I thank you very much! I also appreciated all the other replys... I have enough things to check to keep me busy for awhile. I will let you know what I find. Thank you all again!

 

[SHOracer14]

OK UPDATES! Pulled the timing cover and everything was spot on. I then ran with the timing light and got 20 degrees at each cam and 10 at the crank which is the correct timing at idle (correct?) and had a very smooth linear advance as I went up the rev range. I pulled the MAF with no change, as well as the BARO with no change. There was no slack in the belt (when running at idle it was maybe a half a tooth off between the two cam gears which is normal on most cars I've worked on after the belt stretches slightly when worn in). Also, no crank cancer. That leaves me with checking the fuel pressure and my only other thought is s clogged cat. If those are both fine as everything else has been I am gonna just have to accept the fact that it is a factory slug.

 

[smak]

check the compression lately?

if the rings never seated properly then they all will be lower than usual.

 

[SHOracer14]

check the compression lately?

if the rings never seated properly then they all will be lower than usual.

yeah I actually meant to say check the compression also... I have never tried doing that on an SHO before... Is it possible to check the back three? I figured checking the fronts would give me a good enough idea on what was going on.

 

[davidb]

Could be clloged cats or a piece of the cat broke off and is lodged down stream in the exhaust. Happened to me once. When the piece broke free and moved into the muffler my SHO took off like it had been Goosed. Sometimes it's the simple things.

Dave

 

[SHOracer14]

Checked the fuel pressure today and it ran 39 PSI withe the FPR... I didn't even pull the line as it was more than high enough with it connected. Any more thoughts other than compression check and possible clogged cats??

 

[JoesSHO]

What octane gas are you running? <y old '93 would run noticeably worse with regular unleded than premium, and my '95 doesnt care either way...

I've also learned through my years that many of my cars feel slower than they really are after a while- it's just that I get conditioned to the feeling, and expect more than is really there...

 

[SHOtime2511]

draging break calipers??